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* [PATCH v20 0/9] Free some vmemmap pages of HugeTLB page
@ 2021-04-15  8:39 Muchun Song
  2021-04-15  8:39 ` [PATCH v20 1/9] mm: memory_hotplug: factor out bootmem core functions to bootmem_info.c Muchun Song
                   ` (8 more replies)
  0 siblings, 9 replies; 24+ messages in thread
From: Muchun Song @ 2021-04-15  8:39 UTC (permalink / raw)
  To: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, pawan.kumar.gupta, rdunlap,
	oneukum, anshuman.khandual, jroedel, almasrymina, rientjes,
	willy, osalvador, mhocko, song.bao.hua, david, naoya.horiguchi,
	joao.m.martins
  Cc: duanxiongchun, fam.zheng, linux-doc, linux-kernel, linux-mm,
	linux-fsdevel, Muchun Song

Hi,

Since Mike's patches (make hugetlb put_page safe for all calling contexts[1])
applied into the next-20210412. We can move forward on this patch series now.

This patch series will free some vmemmap pages(struct page structures)
associated with each HugeTLB page when preallocated to save memory.

In order to reduce the difficulty of the first version of code review.
From this version, we disable PMD/huge page mapping of vmemmap if this
feature was enabled. This acutely eliminates a bunch of the complex code
doing page table manipulation. When this patch series is solid, we cam add
the code of vmemmap page table manipulation in the future.

The struct page structures (page structs) are used to describe a physical
page frame. By default, there is an one-to-one mapping from a page frame to
it's corresponding page struct.

The HugeTLB pages consist of multiple base page size pages and is supported
by many architectures. See hugetlbpage.rst in the Documentation directory
for more details. On the x86 architecture, HugeTLB pages of size 2MB and 1GB
are currently supported. Since the base page size on x86 is 4KB, a 2MB
HugeTLB page consists of 512 base pages and a 1GB HugeTLB page consists of
4096 base pages. For each base page, there is a corresponding page struct.

Within the HugeTLB subsystem, only the first 4 page structs are used to
contain unique information about a HugeTLB page. HUGETLB_CGROUP_MIN_ORDER
provides this upper limit. The only 'useful' information in the remaining
page structs is the compound_head field, and this field is the same for all
tail pages.

By removing redundant page structs for HugeTLB pages, memory can returned to
the buddy allocator for other uses.

When the system boot up, every 2M HugeTLB has 512 struct page structs which
size is 8 pages(sizeof(struct page) * 512 / PAGE_SIZE).

    HugeTLB                  struct pages(8 pages)         page frame(8 pages)
 +-----------+ ---virt_to_page---> +-----------+   mapping to   +-----------+
 |           |                     |     0     | -------------> |     0     |
 |           |                     +-----------+                +-----------+
 |           |                     |     1     | -------------> |     1     |
 |           |                     +-----------+                +-----------+
 |           |                     |     2     | -------------> |     2     |
 |           |                     +-----------+                +-----------+
 |           |                     |     3     | -------------> |     3     |
 |           |                     +-----------+                +-----------+
 |           |                     |     4     | -------------> |     4     |
 |    2MB    |                     +-----------+                +-----------+
 |           |                     |     5     | -------------> |     5     |
 |           |                     +-----------+                +-----------+
 |           |                     |     6     | -------------> |     6     |
 |           |                     +-----------+                +-----------+
 |           |                     |     7     | -------------> |     7     |
 |           |                     +-----------+                +-----------+
 |           |
 |           |
 |           |
 +-----------+

The value of page->compound_head is the same for all tail pages. The first
page of page structs (page 0) associated with the HugeTLB page contains the 4
page structs necessary to describe the HugeTLB. The only use of the remaining
pages of page structs (page 1 to page 7) is to point to page->compound_head.
Therefore, we can remap pages 2 to 7 to page 1. Only 2 pages of page structs
will be used for each HugeTLB page. This will allow us to free the remaining
6 pages to the buddy allocator.

Here is how things look after remapping.

    HugeTLB                  struct pages(8 pages)         page frame(8 pages)
 +-----------+ ---virt_to_page---> +-----------+   mapping to   +-----------+
 |           |                     |     0     | -------------> |     0     |
 |           |                     +-----------+                +-----------+
 |           |                     |     1     | -------------> |     1     |
 |           |                     +-----------+                +-----------+
 |           |                     |     2     | ----------------^ ^ ^ ^ ^ ^
 |           |                     +-----------+                   | | | | |
 |           |                     |     3     | ------------------+ | | | |
 |           |                     +-----------+                     | | | |
 |           |                     |     4     | --------------------+ | | |
 |    2MB    |                     +-----------+                       | | |
 |           |                     |     5     | ----------------------+ | |
 |           |                     +-----------+                         | |
 |           |                     |     6     | ------------------------+ |
 |           |                     +-----------+                           |
 |           |                     |     7     | --------------------------+
 |           |                     +-----------+
 |           |
 |           |
 |           |
 +-----------+

When a HugeTLB is freed to the buddy system, we should allocate 6 pages for
vmemmap pages and restore the previous mapping relationship.

Apart from 2MB HugeTLB page, we also have 1GB HugeTLB page. It is similar
to the 2MB HugeTLB page. We also can use this approach to free the vmemmap
pages.

In this case, for the 1GB HugeTLB page, we can save 4094 pages. This is a
very substantial gain. On our server, run some SPDK/QEMU applications which
will use 1024GB HugeTLB page. With this feature enabled, we can save ~16GB
(1G hugepage)/~12GB (2MB hugepage) memory.

Because there are vmemmap page tables reconstruction on the freeing/allocating
path, it increases some overhead. Here are some overhead analysis.

1) Allocating 10240 2MB HugeTLB pages.

   a) With this patch series applied:
   # time echo 10240 > /proc/sys/vm/nr_hugepages

   real     0m0.166s
   user     0m0.000s
   sys      0m0.166s

   # bpftrace -e 'kprobe:alloc_fresh_huge_page { @start[tid] = nsecs; }
     kretprobe:alloc_fresh_huge_page /@start[tid]/ { @latency = hist(nsecs -
     @start[tid]); delete(@start[tid]); }'
   Attaching 2 probes...

   @latency:
   [8K, 16K)           5476 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
   [16K, 32K)          4760 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@       |
   [32K, 64K)             4 |                                                    |

   b) Without this patch series:
   # time echo 10240 > /proc/sys/vm/nr_hugepages

   real     0m0.067s
   user     0m0.000s
   sys      0m0.067s

   # bpftrace -e 'kprobe:alloc_fresh_huge_page { @start[tid] = nsecs; }
     kretprobe:alloc_fresh_huge_page /@start[tid]/ { @latency = hist(nsecs -
     @start[tid]); delete(@start[tid]); }'
   Attaching 2 probes...

   @latency:
   [4K, 8K)           10147 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
   [8K, 16K)             93 |                                                    |

   Summarize: this feature is about ~2x slower than before.

2) Freeing 10240 2MB HugeTLB pages.

   a) With this patch series applied:
   # time echo 0 > /proc/sys/vm/nr_hugepages

   real     0m0.213s
   user     0m0.000s
   sys      0m0.213s

   # bpftrace -e 'kprobe:free_pool_huge_page { @start[tid] = nsecs; }
     kretprobe:free_pool_huge_page /@start[tid]/ { @latency = hist(nsecs -
     @start[tid]); delete(@start[tid]); }'
   Attaching 2 probes...

   @latency:
   [8K, 16K)              6 |                                                    |
   [16K, 32K)         10227 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
   [32K, 64K)             7 |                                                    |

   b) Without this patch series:
   # time echo 0 > /proc/sys/vm/nr_hugepages

   real     0m0.081s
   user     0m0.000s
   sys      0m0.081s

   # bpftrace -e 'kprobe:free_pool_huge_page { @start[tid] = nsecs; }
     kretprobe:free_pool_huge_page /@start[tid]/ { @latency = hist(nsecs -
     @start[tid]); delete(@start[tid]); }'
   Attaching 2 probes...

   @latency:
   [4K, 8K)            6805 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
   [8K, 16K)           3427 |@@@@@@@@@@@@@@@@@@@@@@@@@@                          |
   [16K, 32K)             8 |                                                    |

   Summarize: The overhead of __free_hugepage is about ~2-3x slower than before.

Although the overhead has increased, the overhead is not significant. Like Mike
said, "However, remember that the majority of use cases create HugeTLB pages at
or shortly after boot time and add them to the pool. So, additional overhead is
at pool creation time. There is no change to 'normal run time' operations of
getting a page from or returning a page to the pool (think page fault/unmap)".

Despite the overhead and in addition to the memory gains from this series. The
following data is obtained by Joao Martins. Very thanks to his effort.

There's an additional benefit which is page (un)pinners will see an improvement
and Joao presumes because there are fewer memmap pages and thus the tail/head
pages are staying in cache more often.

Out of the box Joao saw (when comparing linux-next against linux-next + this series)
with gup_test and pinning a 16G HugeTLB file (with 1G pages):

	get_user_pages(): ~32k -> ~9k
	unpin_user_pages(): ~75k -> ~70k

Usually any tight loop fetching compound_head(), or reading tail pages data (e.g.
compound_head) benefit a lot. There's some unpinning inefficiencies Joao was
fixing[2], but with that in added it shows even more:

	unpin_user_pages(): ~27k -> ~3.8k

[1] https://lore.kernel.org/linux-mm/20210409205254.242291-1-mike.kravetz@oracle.com/
[2] https://lore.kernel.org/linux-mm/20210204202500.26474-1-joao.m.martins@oracle.com/

Todo:
  - Free all of the tail vmemmap pages
    Now for the 2MB HugrTLB page, we only free 6 vmemmap pages. we really can
    free 7 vmemmap pages. In this case, we can see 8 of the 512 struct page
    structures has beed set PG_head flag. If we can adjust compound_head()
    slightly and make compound_head() return the real head struct page when
    the parameter is the tail struct page but with PG_head flag set.

    In order to make the code evolution route clearer. This feature can can be
    a separate patch after this patchset is solid.

  - Support for other architectures (e.g. aarch64).
  - Enable PMD/huge page mapping of vmemmap even if this feature was enabled.

Changelog in v19 -> v20:
  - Rebase to next-20210412.
  - Introduce workqueue to defer freeing HugeTLB pages.
  - Remove all tags (Reviewed-by ot Tested-by) from patch 6.
  - Disable memmap_on_memory when hugetlb_free_vmemmap enabled (patch 8).

Changelog in v18 -> v19:
  - Fix compiler error on sparc arch. Thanks Stephen.
  - Make patch "gather discrete indexes of tail page" prior to "free the vmemmap
    pages associated with each HugeTLB page".
  - Remove some BUG_ON from patch #4.
  - Update patch #6 changelog.
  - Update Documentation/admin-guide/mm/memory-hotplug.rst.
  - Drop the patch of "optimize the code with the help of the compiler".
  - Update Documentation/admin-guide/kernel-parameters.txt in patch #7.
  - Trim update_and_free_page.

 Thanks to Michal, Oscar and Mike's review and suggestions.

Changelog in v17 -> v18:
  - Add complete copyright to bootmem_info.c (Suggested by Balbir).
  - Fix some issues (in patch #4) suggested by Mike.

  Thanks to Balbir and Mike's review. Also thanks to Chen Huang and
  Bodeddula Balasubramaniam's test.

Changelog in v16 -> v17:
  - Fix issues suggested by Mike and Oscar.
  - Update commit log suggested by Michal.

  Thanks to Mike, David H and Michal's suggestions and review.

Changelog in v15 -> v16:
  - Use GFP_KERNEL to allocate vmemmap pages.

  Thanks to Mike, David H and Michal's suggestions.

Changelog in v14 -> v15:
  - Fix some issues suggested by Oscar. Thanks to Oscar.
  - Add numbers which Joao Martins tested to cover letter. Thanks to his effort.

Changelog in v13 -> v14:
  - Refuse to free the HugeTLB page when the system is under memory pressure.
  - Use GFP_ATOMIC to allocate vmemmap pages instead of GFP_KERNEL.
  - Rebase to linux-next 20210202.
  - Fix and add some comments for vmemmap_remap_free().

  Thanks to Oscar, Mike, David H and David R's suggestions and review.

Changelog in v12 -> v13:
  - Remove VM_WARN_ON_PAGE macro.
  - Add more comments in vmemmap_pte_range() and vmemmap_remap_free().

  Thanks to Oscar and Mike's suggestions and review.

Changelog in v11 -> v12:
  - Move VM_WARN_ON_PAGE to a separate patch.
  - Call __free_hugepage() with hugetlb_lock (See patch #5.) to serialize
    with dissolve_free_huge_page(). It is to prepare for patch #9.
  - Introduce PageHugeInflight. See patch #9.

Changelog in v10 -> v11:
  - Fix compiler error when !CONFIG_HUGETLB_PAGE_FREE_VMEMMAP.
  - Rework some comments and commit changes.
  - Rework vmemmap_remap_free() to 3 parameters.

  Thanks to Oscar and Mike's suggestions and review.

Changelog in v9 -> v10:
  - Fix a bug in patch #11. Thanks to Oscar for pointing that out.
  - Rework some commit log or comments. Thanks Mike and Oscar for the suggestions.
  - Drop VMEMMAP_TAIL_PAGE_REUSE in the patch #3.

  Thank you very much Mike and Oscar for reviewing the code.

Changelog in v8 -> v9:
  - Rework some code. Very thanks to Oscar.
  - Put all the non-hugetlb vmemmap functions under sparsemem-vmemmap.c.

Changelog in v7 -> v8:
  - Adjust the order of patches.

  Very thanks to David and Oscar. Your suggestions are very valuable.

Changelog in v6 -> v7:
  - Rebase to linux-next 20201130
  - Do not use basepage mapping for vmemmap when this feature is disabled.
  - Rework some patchs.
    [PATCH v6 08/16] mm/hugetlb: Free the vmemmap pages associated with each hugetlb page
    [PATCH v6 10/16] mm/hugetlb: Allocate the vmemmap pages associated with each hugetlb page

  Thanks to Oscar and Barry.

Changelog in v5 -> v6:
  - Disable PMD/huge page mapping of vmemmap if this feature was enabled.
  - Simplify the first version code.

Changelog in v4 -> v5:
  - Rework somme comments and code in the [PATCH v4 04/21] and [PATCH v4 05/21].

  Thanks to Mike and Oscar's suggestions.

Changelog in v3 -> v4:
  - Move all the vmemmap functions to hugetlb_vmemmap.c.
  - Make the CONFIG_HUGETLB_PAGE_FREE_VMEMMAP default to y, if we want to
    disable this feature, we should disable it by a boot/kernel command line.
  - Remove vmemmap_pgtable_{init, deposit, withdraw}() helper functions.
  - Initialize page table lock for vmemmap through core_initcall mechanism.

  Thanks for Mike and Oscar's suggestions.

Changelog in v2 -> v3:
  - Rename some helps function name. Thanks Mike.
  - Rework some code. Thanks Mike and Oscar.
  - Remap the tail vmemmap page with PAGE_KERNEL_RO instead of PAGE_KERNEL.
    Thanks Matthew.
  - Add some overhead analysis in the cover letter.
  - Use vmemap pmd table lock instead of a hugetlb specific global lock.

Changelog in v1 -> v2:
  - Fix do not call dissolve_compound_page in alloc_huge_page_vmemmap().
  - Fix some typo and code style problems.
  - Remove unused handle_vmemmap_fault().
  - Merge some commits to one commit suggested by Mike.

Muchun Song (9):
  mm: memory_hotplug: factor out bootmem core functions to
    bootmem_info.c
  mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP
  mm: hugetlb: gather discrete indexes of tail page
  mm: hugetlb: free the vmemmap pages associated with each HugeTLB page
  mm: hugetlb: defer freeing of HugeTLB pages
  mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap
  mm: memory_hotplug: disable memmap_on_memory when hugetlb_free_vmemmap
    enabled
  mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate

 Documentation/admin-guide/kernel-parameters.txt |  21 ++
 Documentation/admin-guide/mm/hugetlbpage.rst    |  11 +
 Documentation/admin-guide/mm/memory-hotplug.rst |  13 ++
 arch/sparc/mm/init_64.c                         |   1 +
 arch/x86/mm/init_64.c                           |  13 +-
 drivers/acpi/acpi_memhotplug.c                  |   1 +
 fs/Kconfig                                      |   5 +
 include/linux/bootmem_info.h                    |  66 ++++++
 include/linux/hugetlb.h                         |  46 +++-
 include/linux/hugetlb_cgroup.h                  |  19 +-
 include/linux/memory_hotplug.h                  |  27 ---
 include/linux/mm.h                              |   5 +
 mm/Makefile                                     |   2 +
 mm/bootmem_info.c                               | 127 ++++++++++
 mm/hugetlb.c                                    | 157 +++++++++++--
 mm/hugetlb_vmemmap.c                            | 297 ++++++++++++++++++++++++
 mm/hugetlb_vmemmap.h                            |  45 ++++
 mm/memory_hotplug.c                             | 134 ++---------
 mm/sparse-vmemmap.c                             | 267 +++++++++++++++++++++
 mm/sparse.c                                     |   1 +
 20 files changed, 1078 insertions(+), 180 deletions(-)
 create mode 100644 include/linux/bootmem_info.h
 create mode 100644 mm/bootmem_info.c
 create mode 100644 mm/hugetlb_vmemmap.c
 create mode 100644 mm/hugetlb_vmemmap.h

-- 
2.11.0


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [PATCH v20 1/9] mm: memory_hotplug: factor out bootmem core functions to bootmem_info.c
  2021-04-15  8:39 [PATCH v20 0/9] Free some vmemmap pages of HugeTLB page Muchun Song
@ 2021-04-15  8:39 ` Muchun Song
  2021-04-15  8:39 ` [PATCH v20 2/9] mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
                   ` (7 subsequent siblings)
  8 siblings, 0 replies; 24+ messages in thread
From: Muchun Song @ 2021-04-15  8:39 UTC (permalink / raw)
  To: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, pawan.kumar.gupta, rdunlap,
	oneukum, anshuman.khandual, jroedel, almasrymina, rientjes,
	willy, osalvador, mhocko, song.bao.hua, david, naoya.horiguchi,
	joao.m.martins
  Cc: duanxiongchun, fam.zheng, linux-doc, linux-kernel, linux-mm,
	linux-fsdevel, Muchun Song, Miaohe Lin, Chen Huang,
	Bodeddula Balasubramaniam

Move bootmem info registration common API to individual bootmem_info.c.
And we will use {get,put}_page_bootmem() to initialize the page for the
vmemmap pages or free the vmemmap pages to buddy in the later patch.
So move them out of CONFIG_MEMORY_HOTPLUG_SPARSE. This is just code
movement without any functional change.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Tested-by: Chen Huang <chenhuang5@huawei.com>
Tested-by: Bodeddula Balasubramaniam <bodeddub@amazon.com>
---
 arch/sparc/mm/init_64.c        |   1 +
 arch/x86/mm/init_64.c          |   3 +-
 include/linux/bootmem_info.h   |  40 +++++++++++++
 include/linux/memory_hotplug.h |  27 ---------
 mm/Makefile                    |   1 +
 mm/bootmem_info.c              | 127 +++++++++++++++++++++++++++++++++++++++++
 mm/memory_hotplug.c            | 116 -------------------------------------
 mm/sparse.c                    |   1 +
 8 files changed, 172 insertions(+), 144 deletions(-)
 create mode 100644 include/linux/bootmem_info.h
 create mode 100644 mm/bootmem_info.c

diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c
index e454f179cf5d..ac9d8b161e0c 100644
--- a/arch/sparc/mm/init_64.c
+++ b/arch/sparc/mm/init_64.c
@@ -27,6 +27,7 @@
 #include <linux/percpu.h>
 #include <linux/mmzone.h>
 #include <linux/gfp.h>
+#include <linux/bootmem_info.h>
 
 #include <asm/head.h>
 #include <asm/page.h>
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index e527d829e1ed..3aaf1d30c777 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -33,6 +33,7 @@
 #include <linux/nmi.h>
 #include <linux/gfp.h>
 #include <linux/kcore.h>
+#include <linux/bootmem_info.h>
 
 #include <asm/processor.h>
 #include <asm/bios_ebda.h>
@@ -1623,7 +1624,7 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 	return err;
 }
 
-#if defined(CONFIG_MEMORY_HOTPLUG_SPARSE) && defined(CONFIG_HAVE_BOOTMEM_INFO_NODE)
+#ifdef CONFIG_HAVE_BOOTMEM_INFO_NODE
 void register_page_bootmem_memmap(unsigned long section_nr,
 				  struct page *start_page, unsigned long nr_pages)
 {
diff --git a/include/linux/bootmem_info.h b/include/linux/bootmem_info.h
new file mode 100644
index 000000000000..4ed6dee1adc9
--- /dev/null
+++ b/include/linux/bootmem_info.h
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_BOOTMEM_INFO_H
+#define __LINUX_BOOTMEM_INFO_H
+
+#include <linux/mmzone.h>
+
+/*
+ * Types for free bootmem stored in page->lru.next. These have to be in
+ * some random range in unsigned long space for debugging purposes.
+ */
+enum {
+	MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE = 12,
+	SECTION_INFO = MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE,
+	MIX_SECTION_INFO,
+	NODE_INFO,
+	MEMORY_HOTPLUG_MAX_BOOTMEM_TYPE = NODE_INFO,
+};
+
+#ifdef CONFIG_HAVE_BOOTMEM_INFO_NODE
+void __init register_page_bootmem_info_node(struct pglist_data *pgdat);
+
+void get_page_bootmem(unsigned long info, struct page *page,
+		      unsigned long type);
+void put_page_bootmem(struct page *page);
+#else
+static inline void register_page_bootmem_info_node(struct pglist_data *pgdat)
+{
+}
+
+static inline void put_page_bootmem(struct page *page)
+{
+}
+
+static inline void get_page_bootmem(unsigned long info, struct page *page,
+				    unsigned long type)
+{
+}
+#endif
+
+#endif /* __LINUX_BOOTMEM_INFO_H */
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index a85d4b7d15c2..ff1449f645f1 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -18,18 +18,6 @@ struct vmem_altmap;
 #ifdef CONFIG_MEMORY_HOTPLUG
 struct page *pfn_to_online_page(unsigned long pfn);
 
-/*
- * Types for free bootmem stored in page->lru.next. These have to be in
- * some random range in unsigned long space for debugging purposes.
- */
-enum {
-	MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE = 12,
-	SECTION_INFO = MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE,
-	MIX_SECTION_INFO,
-	NODE_INFO,
-	MEMORY_HOTPLUG_MAX_BOOTMEM_TYPE = NODE_INFO,
-};
-
 /* Types for control the zone type of onlined and offlined memory */
 enum {
 	/* Offline the memory. */
@@ -220,17 +208,6 @@ static inline void arch_refresh_nodedata(int nid, pg_data_t *pgdat)
 #endif /* CONFIG_NUMA */
 #endif /* CONFIG_HAVE_ARCH_NODEDATA_EXTENSION */
 
-#ifdef CONFIG_HAVE_BOOTMEM_INFO_NODE
-extern void __init register_page_bootmem_info_node(struct pglist_data *pgdat);
-#else
-static inline void register_page_bootmem_info_node(struct pglist_data *pgdat)
-{
-}
-#endif
-extern void put_page_bootmem(struct page *page);
-extern void get_page_bootmem(unsigned long ingo, struct page *page,
-			     unsigned long type);
-
 void get_online_mems(void);
 void put_online_mems(void);
 
@@ -258,10 +235,6 @@ static inline void zone_span_writelock(struct zone *zone) {}
 static inline void zone_span_writeunlock(struct zone *zone) {}
 static inline void zone_seqlock_init(struct zone *zone) {}
 
-static inline void register_page_bootmem_info_node(struct pglist_data *pgdat)
-{
-}
-
 static inline int try_online_node(int nid)
 {
 	return 0;
diff --git a/mm/Makefile b/mm/Makefile
index a9ad6122d468..d0ccddae7a45 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -126,3 +126,4 @@ obj-$(CONFIG_MAPPING_DIRTY_HELPERS) += mapping_dirty_helpers.o
 obj-$(CONFIG_PTDUMP_CORE) += ptdump.o
 obj-$(CONFIG_PAGE_REPORTING) += page_reporting.o
 obj-$(CONFIG_IO_MAPPING) += io-mapping.o
+obj-$(CONFIG_HAVE_BOOTMEM_INFO_NODE) += bootmem_info.o
diff --git a/mm/bootmem_info.c b/mm/bootmem_info.c
new file mode 100644
index 000000000000..5b152dba7344
--- /dev/null
+++ b/mm/bootmem_info.c
@@ -0,0 +1,127 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Bootmem core functions.
+ *
+ * Copyright (c) 2020, Bytedance.
+ *
+ *     Author: Muchun Song <songmuchun@bytedance.com>
+ *
+ */
+#include <linux/mm.h>
+#include <linux/compiler.h>
+#include <linux/memblock.h>
+#include <linux/bootmem_info.h>
+#include <linux/memory_hotplug.h>
+
+void get_page_bootmem(unsigned long info, struct page *page, unsigned long type)
+{
+	page->freelist = (void *)type;
+	SetPagePrivate(page);
+	set_page_private(page, info);
+	page_ref_inc(page);
+}
+
+void put_page_bootmem(struct page *page)
+{
+	unsigned long type;
+
+	type = (unsigned long) page->freelist;
+	BUG_ON(type < MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE ||
+	       type > MEMORY_HOTPLUG_MAX_BOOTMEM_TYPE);
+
+	if (page_ref_dec_return(page) == 1) {
+		page->freelist = NULL;
+		ClearPagePrivate(page);
+		set_page_private(page, 0);
+		INIT_LIST_HEAD(&page->lru);
+		free_reserved_page(page);
+	}
+}
+
+#ifndef CONFIG_SPARSEMEM_VMEMMAP
+static void register_page_bootmem_info_section(unsigned long start_pfn)
+{
+	unsigned long mapsize, section_nr, i;
+	struct mem_section *ms;
+	struct page *page, *memmap;
+	struct mem_section_usage *usage;
+
+	section_nr = pfn_to_section_nr(start_pfn);
+	ms = __nr_to_section(section_nr);
+
+	/* Get section's memmap address */
+	memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);
+
+	/*
+	 * Get page for the memmap's phys address
+	 * XXX: need more consideration for sparse_vmemmap...
+	 */
+	page = virt_to_page(memmap);
+	mapsize = sizeof(struct page) * PAGES_PER_SECTION;
+	mapsize = PAGE_ALIGN(mapsize) >> PAGE_SHIFT;
+
+	/* remember memmap's page */
+	for (i = 0; i < mapsize; i++, page++)
+		get_page_bootmem(section_nr, page, SECTION_INFO);
+
+	usage = ms->usage;
+	page = virt_to_page(usage);
+
+	mapsize = PAGE_ALIGN(mem_section_usage_size()) >> PAGE_SHIFT;
+
+	for (i = 0; i < mapsize; i++, page++)
+		get_page_bootmem(section_nr, page, MIX_SECTION_INFO);
+
+}
+#else /* CONFIG_SPARSEMEM_VMEMMAP */
+static void register_page_bootmem_info_section(unsigned long start_pfn)
+{
+	unsigned long mapsize, section_nr, i;
+	struct mem_section *ms;
+	struct page *page, *memmap;
+	struct mem_section_usage *usage;
+
+	section_nr = pfn_to_section_nr(start_pfn);
+	ms = __nr_to_section(section_nr);
+
+	memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);
+
+	register_page_bootmem_memmap(section_nr, memmap, PAGES_PER_SECTION);
+
+	usage = ms->usage;
+	page = virt_to_page(usage);
+
+	mapsize = PAGE_ALIGN(mem_section_usage_size()) >> PAGE_SHIFT;
+
+	for (i = 0; i < mapsize; i++, page++)
+		get_page_bootmem(section_nr, page, MIX_SECTION_INFO);
+}
+#endif /* !CONFIG_SPARSEMEM_VMEMMAP */
+
+void __init register_page_bootmem_info_node(struct pglist_data *pgdat)
+{
+	unsigned long i, pfn, end_pfn, nr_pages;
+	int node = pgdat->node_id;
+	struct page *page;
+
+	nr_pages = PAGE_ALIGN(sizeof(struct pglist_data)) >> PAGE_SHIFT;
+	page = virt_to_page(pgdat);
+
+	for (i = 0; i < nr_pages; i++, page++)
+		get_page_bootmem(node, page, NODE_INFO);
+
+	pfn = pgdat->node_start_pfn;
+	end_pfn = pgdat_end_pfn(pgdat);
+
+	/* register section info */
+	for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
+		/*
+		 * Some platforms can assign the same pfn to multiple nodes - on
+		 * node0 as well as nodeN.  To avoid registering a pfn against
+		 * multiple nodes we check that this pfn does not already
+		 * reside in some other nodes.
+		 */
+		if (pfn_valid(pfn) && (early_pfn_to_nid(pfn) == node))
+			register_page_bootmem_info_section(pfn);
+	}
+}
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 446f5aa373b7..68923c19bdea 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -154,122 +154,6 @@ static void release_memory_resource(struct resource *res)
 }
 
 #ifdef CONFIG_MEMORY_HOTPLUG_SPARSE
-void get_page_bootmem(unsigned long info,  struct page *page,
-		      unsigned long type)
-{
-	page->freelist = (void *)type;
-	SetPagePrivate(page);
-	set_page_private(page, info);
-	page_ref_inc(page);
-}
-
-void put_page_bootmem(struct page *page)
-{
-	unsigned long type;
-
-	type = (unsigned long) page->freelist;
-	BUG_ON(type < MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE ||
-	       type > MEMORY_HOTPLUG_MAX_BOOTMEM_TYPE);
-
-	if (page_ref_dec_return(page) == 1) {
-		page->freelist = NULL;
-		ClearPagePrivate(page);
-		set_page_private(page, 0);
-		INIT_LIST_HEAD(&page->lru);
-		free_reserved_page(page);
-	}
-}
-
-#ifdef CONFIG_HAVE_BOOTMEM_INFO_NODE
-#ifndef CONFIG_SPARSEMEM_VMEMMAP
-static void register_page_bootmem_info_section(unsigned long start_pfn)
-{
-	unsigned long mapsize, section_nr, i;
-	struct mem_section *ms;
-	struct page *page, *memmap;
-	struct mem_section_usage *usage;
-
-	section_nr = pfn_to_section_nr(start_pfn);
-	ms = __nr_to_section(section_nr);
-
-	/* Get section's memmap address */
-	memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);
-
-	/*
-	 * Get page for the memmap's phys address
-	 * XXX: need more consideration for sparse_vmemmap...
-	 */
-	page = virt_to_page(memmap);
-	mapsize = sizeof(struct page) * PAGES_PER_SECTION;
-	mapsize = PAGE_ALIGN(mapsize) >> PAGE_SHIFT;
-
-	/* remember memmap's page */
-	for (i = 0; i < mapsize; i++, page++)
-		get_page_bootmem(section_nr, page, SECTION_INFO);
-
-	usage = ms->usage;
-	page = virt_to_page(usage);
-
-	mapsize = PAGE_ALIGN(mem_section_usage_size()) >> PAGE_SHIFT;
-
-	for (i = 0; i < mapsize; i++, page++)
-		get_page_bootmem(section_nr, page, MIX_SECTION_INFO);
-
-}
-#else /* CONFIG_SPARSEMEM_VMEMMAP */
-static void register_page_bootmem_info_section(unsigned long start_pfn)
-{
-	unsigned long mapsize, section_nr, i;
-	struct mem_section *ms;
-	struct page *page, *memmap;
-	struct mem_section_usage *usage;
-
-	section_nr = pfn_to_section_nr(start_pfn);
-	ms = __nr_to_section(section_nr);
-
-	memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);
-
-	register_page_bootmem_memmap(section_nr, memmap, PAGES_PER_SECTION);
-
-	usage = ms->usage;
-	page = virt_to_page(usage);
-
-	mapsize = PAGE_ALIGN(mem_section_usage_size()) >> PAGE_SHIFT;
-
-	for (i = 0; i < mapsize; i++, page++)
-		get_page_bootmem(section_nr, page, MIX_SECTION_INFO);
-}
-#endif /* !CONFIG_SPARSEMEM_VMEMMAP */
-
-void __init register_page_bootmem_info_node(struct pglist_data *pgdat)
-{
-	unsigned long i, pfn, end_pfn, nr_pages;
-	int node = pgdat->node_id;
-	struct page *page;
-
-	nr_pages = PAGE_ALIGN(sizeof(struct pglist_data)) >> PAGE_SHIFT;
-	page = virt_to_page(pgdat);
-
-	for (i = 0; i < nr_pages; i++, page++)
-		get_page_bootmem(node, page, NODE_INFO);
-
-	pfn = pgdat->node_start_pfn;
-	end_pfn = pgdat_end_pfn(pgdat);
-
-	/* register section info */
-	for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
-		/*
-		 * Some platforms can assign the same pfn to multiple nodes - on
-		 * node0 as well as nodeN.  To avoid registering a pfn against
-		 * multiple nodes we check that this pfn does not already
-		 * reside in some other nodes.
-		 */
-		if (pfn_valid(pfn) && (early_pfn_to_nid(pfn) == node))
-			register_page_bootmem_info_section(pfn);
-	}
-}
-#endif /* CONFIG_HAVE_BOOTMEM_INFO_NODE */
-
 static int check_pfn_span(unsigned long pfn, unsigned long nr_pages,
 		const char *reason)
 {
diff --git a/mm/sparse.c b/mm/sparse.c
index 522ebb1a4b64..2533c7390fa9 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -13,6 +13,7 @@
 #include <linux/vmalloc.h>
 #include <linux/swap.h>
 #include <linux/swapops.h>
+#include <linux/bootmem_info.h>
 
 #include "internal.h"
 #include <asm/dma.h>
-- 
2.11.0


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [PATCH v20 2/9] mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP
  2021-04-15  8:39 [PATCH v20 0/9] Free some vmemmap pages of HugeTLB page Muchun Song
  2021-04-15  8:39 ` [PATCH v20 1/9] mm: memory_hotplug: factor out bootmem core functions to bootmem_info.c Muchun Song
@ 2021-04-15  8:39 ` Muchun Song
  2021-04-15  8:39 ` [PATCH v20 3/9] mm: hugetlb: gather discrete indexes of tail page Muchun Song
                   ` (6 subsequent siblings)
  8 siblings, 0 replies; 24+ messages in thread
From: Muchun Song @ 2021-04-15  8:39 UTC (permalink / raw)
  To: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, pawan.kumar.gupta, rdunlap,
	oneukum, anshuman.khandual, jroedel, almasrymina, rientjes,
	willy, osalvador, mhocko, song.bao.hua, david, naoya.horiguchi,
	joao.m.martins
  Cc: duanxiongchun, fam.zheng, linux-doc, linux-kernel, linux-mm,
	linux-fsdevel, Muchun Song, Miaohe Lin, Chen Huang,
	Bodeddula Balasubramaniam, Balbir Singh

The option HUGETLB_PAGE_FREE_VMEMMAP allows for the freeing of
some vmemmap pages associated with pre-allocated HugeTLB pages.
For example, on X86_64 6 vmemmap pages of size 4KB each can be
saved for each 2MB HugeTLB page. 4094 vmemmap pages of size 4KB
each can be saved for each 1GB HugeTLB page.

When a HugeTLB page is allocated or freed, the vmemmap array
representing the range associated with the page will need to be
remapped. When a page is allocated, vmemmap pages are freed
after remapping. When a page is freed, previously discarded
vmemmap pages must be allocated before remapping.

The config option is introduced early so that supporting code
can be written to depend on the option. The initial version of
the code only provides support for x86-64.

If config HAVE_BOOTMEM_INFO_NODE is enabled, the freeing vmemmap
page code denpend on it to free vmemmap pages. Otherwise, just
use free_reserved_page() to free vmemmmap pages. The routine
register_page_bootmem_info() is used to register bootmem info.
Therefore, make sure register_page_bootmem_info is enabled if
HUGETLB_PAGE_FREE_VMEMMAP is defined.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Tested-by: Chen Huang <chenhuang5@huawei.com>
Tested-by: Bodeddula Balasubramaniam <bodeddub@amazon.com>
Reviewed-by: Balbir Singh <bsingharora@gmail.com>
---
 arch/x86/mm/init_64.c | 2 +-
 fs/Kconfig            | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 3aaf1d30c777..65ea58527176 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1270,7 +1270,7 @@ static struct kcore_list kcore_vsyscall;
 
 static void __init register_page_bootmem_info(void)
 {
-#ifdef CONFIG_NUMA
+#if defined(CONFIG_NUMA) || defined(CONFIG_HUGETLB_PAGE_FREE_VMEMMAP)
 	int i;
 
 	for_each_online_node(i)
diff --git a/fs/Kconfig b/fs/Kconfig
index dcd9161fbeba..6ce6fdac00a3 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -240,6 +240,11 @@ config HUGETLBFS
 config HUGETLB_PAGE
 	def_bool HUGETLBFS
 
+config HUGETLB_PAGE_FREE_VMEMMAP
+	def_bool HUGETLB_PAGE
+	depends on X86_64
+	depends on SPARSEMEM_VMEMMAP
+
 config MEMFD_CREATE
 	def_bool TMPFS || HUGETLBFS
 
-- 
2.11.0


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [PATCH v20 3/9] mm: hugetlb: gather discrete indexes of tail page
  2021-04-15  8:39 [PATCH v20 0/9] Free some vmemmap pages of HugeTLB page Muchun Song
  2021-04-15  8:39 ` [PATCH v20 1/9] mm: memory_hotplug: factor out bootmem core functions to bootmem_info.c Muchun Song
  2021-04-15  8:39 ` [PATCH v20 2/9] mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
@ 2021-04-15  8:39 ` Muchun Song
  2021-04-16 18:54   ` Mike Kravetz
  2021-04-15  8:40 ` [PATCH v20 4/9] mm: hugetlb: free the vmemmap pages associated with each HugeTLB page Muchun Song
                   ` (5 subsequent siblings)
  8 siblings, 1 reply; 24+ messages in thread
From: Muchun Song @ 2021-04-15  8:39 UTC (permalink / raw)
  To: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, pawan.kumar.gupta, rdunlap,
	oneukum, anshuman.khandual, jroedel, almasrymina, rientjes,
	willy, osalvador, mhocko, song.bao.hua, david, naoya.horiguchi,
	joao.m.martins
  Cc: duanxiongchun, fam.zheng, linux-doc, linux-kernel, linux-mm,
	linux-fsdevel, Muchun Song, Miaohe Lin, Chen Huang,
	Bodeddula Balasubramaniam

For HugeTLB page, there are more metadata to save in the struct page.
But the head struct page cannot meet our needs, so we have to abuse
other tail struct page to store the metadata. In order to avoid
conflicts caused by subsequent use of more tail struct pages, we can
gather these discrete indexes of tail struct page. In this case, it
will be easier to add a new tail page index later.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Tested-by: Chen Huang <chenhuang5@huawei.com>
Tested-by: Bodeddula Balasubramaniam <bodeddub@amazon.com>
Acked-by: Michal Hocko <mhocko@suse.com>
---
 include/linux/hugetlb.h        | 21 +++++++++++++++++++--
 include/linux/hugetlb_cgroup.h | 19 +++++++++++--------
 2 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 09f1fd12a6fa..0abed7e766b8 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -29,6 +29,23 @@ typedef struct { unsigned long pd; } hugepd_t;
 #include <linux/shm.h>
 #include <asm/tlbflush.h>
 
+/*
+ * For HugeTLB page, there are more metadata to save in the struct page. But
+ * the head struct page cannot meet our needs, so we have to abuse other tail
+ * struct page to store the metadata. In order to avoid conflicts caused by
+ * subsequent use of more tail struct pages, we gather these discrete indexes
+ * of tail struct page here.
+ */
+enum {
+	SUBPAGE_INDEX_SUBPOOL = 1,	/* reuse page->private */
+#ifdef CONFIG_CGROUP_HUGETLB
+	SUBPAGE_INDEX_CGROUP,		/* reuse page->private */
+	SUBPAGE_INDEX_CGROUP_RSVD,	/* reuse page->private */
+	__MAX_CGROUP_SUBPAGE_INDEX = SUBPAGE_INDEX_CGROUP_RSVD,
+#endif
+	__NR_USED_SUBPAGE,
+};
+
 struct hugepage_subpool {
 	spinlock_t lock;
 	long count;
@@ -626,13 +643,13 @@ extern unsigned int default_hstate_idx;
  */
 static inline struct hugepage_subpool *hugetlb_page_subpool(struct page *hpage)
 {
-	return (struct hugepage_subpool *)(hpage+1)->private;
+	return (void *)page_private(hpage + SUBPAGE_INDEX_SUBPOOL);
 }
 
 static inline void hugetlb_set_page_subpool(struct page *hpage,
 					struct hugepage_subpool *subpool)
 {
-	set_page_private(hpage+1, (unsigned long)subpool);
+	set_page_private(hpage + SUBPAGE_INDEX_SUBPOOL, (unsigned long)subpool);
 }
 
 static inline struct hstate *hstate_file(struct file *f)
diff --git a/include/linux/hugetlb_cgroup.h b/include/linux/hugetlb_cgroup.h
index 0bff345c4bc6..0b8d1fdda3a1 100644
--- a/include/linux/hugetlb_cgroup.h
+++ b/include/linux/hugetlb_cgroup.h
@@ -21,15 +21,16 @@ struct hugetlb_cgroup;
 struct resv_map;
 struct file_region;
 
+#ifdef CONFIG_CGROUP_HUGETLB
 /*
  * Minimum page order trackable by hugetlb cgroup.
  * At least 4 pages are necessary for all the tracking information.
- * The second tail page (hpage[2]) is the fault usage cgroup.
- * The third tail page (hpage[3]) is the reservation usage cgroup.
+ * The second tail page (hpage[SUBPAGE_INDEX_CGROUP]) is the fault
+ * usage cgroup. The third tail page (hpage[SUBPAGE_INDEX_CGROUP_RSVD])
+ * is the reservation usage cgroup.
  */
-#define HUGETLB_CGROUP_MIN_ORDER	2
+#define HUGETLB_CGROUP_MIN_ORDER order_base_2(__MAX_CGROUP_SUBPAGE_INDEX + 1)
 
-#ifdef CONFIG_CGROUP_HUGETLB
 enum hugetlb_memory_event {
 	HUGETLB_MAX,
 	HUGETLB_NR_MEMORY_EVENTS,
@@ -66,9 +67,9 @@ __hugetlb_cgroup_from_page(struct page *page, bool rsvd)
 	if (compound_order(page) < HUGETLB_CGROUP_MIN_ORDER)
 		return NULL;
 	if (rsvd)
-		return (struct hugetlb_cgroup *)page[3].private;
+		return (void *)page_private(page + SUBPAGE_INDEX_CGROUP_RSVD);
 	else
-		return (struct hugetlb_cgroup *)page[2].private;
+		return (void *)page_private(page + SUBPAGE_INDEX_CGROUP);
 }
 
 static inline struct hugetlb_cgroup *hugetlb_cgroup_from_page(struct page *page)
@@ -90,9 +91,11 @@ static inline int __set_hugetlb_cgroup(struct page *page,
 	if (compound_order(page) < HUGETLB_CGROUP_MIN_ORDER)
 		return -1;
 	if (rsvd)
-		page[3].private = (unsigned long)h_cg;
+		set_page_private(page + SUBPAGE_INDEX_CGROUP_RSVD,
+				 (unsigned long)h_cg);
 	else
-		page[2].private = (unsigned long)h_cg;
+		set_page_private(page + SUBPAGE_INDEX_CGROUP,
+				 (unsigned long)h_cg);
 	return 0;
 }
 
-- 
2.11.0


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [PATCH v20 4/9] mm: hugetlb: free the vmemmap pages associated with each HugeTLB page
  2021-04-15  8:39 [PATCH v20 0/9] Free some vmemmap pages of HugeTLB page Muchun Song
                   ` (2 preceding siblings ...)
  2021-04-15  8:39 ` [PATCH v20 3/9] mm: hugetlb: gather discrete indexes of tail page Muchun Song
@ 2021-04-15  8:40 ` Muchun Song
  2021-04-16 21:10   ` Mike Kravetz
  2021-04-15  8:40 ` [PATCH v20 5/9] mm: hugetlb: defer freeing of HugeTLB pages Muchun Song
                   ` (4 subsequent siblings)
  8 siblings, 1 reply; 24+ messages in thread
From: Muchun Song @ 2021-04-15  8:40 UTC (permalink / raw)
  To: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, pawan.kumar.gupta, rdunlap,
	oneukum, anshuman.khandual, jroedel, almasrymina, rientjes,
	willy, osalvador, mhocko, song.bao.hua, david, naoya.horiguchi,
	joao.m.martins
  Cc: duanxiongchun, fam.zheng, linux-doc, linux-kernel, linux-mm,
	linux-fsdevel, Muchun Song, Chen Huang,
	Bodeddula Balasubramaniam

Every HugeTLB has more than one struct page structure. We __know__ that
we only use the first 4 (__NR_USED_SUBPAGE) struct page structures
to store metadata associated with each HugeTLB.

There are a lot of struct page structures associated with each HugeTLB
page. For tail pages, the value of compound_head is the same. So we can
reuse first page of tail page structures. We map the virtual addresses
of the remaining pages of tail page structures to the first tail page
struct, and then free these page frames. Therefore, we need to reserve
two pages as vmemmap areas.

When we allocate a HugeTLB page from the buddy, we can free some vmemmap
pages associated with each HugeTLB page. It is more appropriate to do it
in the prep_new_huge_page().

The free_vmemmap_pages_per_hpage(), which indicates how many vmemmap
pages associated with a HugeTLB page can be freed, returns zero for
now, which means the feature is disabled. We will enable it once all
the infrastructure is there.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Tested-by: Chen Huang <chenhuang5@huawei.com>
Tested-by: Bodeddula Balasubramaniam <bodeddub@amazon.com>
Acked-by: Michal Hocko <mhocko@suse.com>
---
 include/linux/bootmem_info.h |  28 +++++-
 include/linux/mm.h           |   3 +
 mm/Makefile                  |   1 +
 mm/hugetlb.c                 |   2 +
 mm/hugetlb_vmemmap.c         | 218 +++++++++++++++++++++++++++++++++++++++++++
 mm/hugetlb_vmemmap.h         |  20 ++++
 mm/sparse-vmemmap.c          | 194 ++++++++++++++++++++++++++++++++++++++
 7 files changed, 465 insertions(+), 1 deletion(-)
 create mode 100644 mm/hugetlb_vmemmap.c
 create mode 100644 mm/hugetlb_vmemmap.h

diff --git a/include/linux/bootmem_info.h b/include/linux/bootmem_info.h
index 4ed6dee1adc9..2bc8b1f69c93 100644
--- a/include/linux/bootmem_info.h
+++ b/include/linux/bootmem_info.h
@@ -2,7 +2,7 @@
 #ifndef __LINUX_BOOTMEM_INFO_H
 #define __LINUX_BOOTMEM_INFO_H
 
-#include <linux/mmzone.h>
+#include <linux/mm.h>
 
 /*
  * Types for free bootmem stored in page->lru.next. These have to be in
@@ -22,6 +22,27 @@ void __init register_page_bootmem_info_node(struct pglist_data *pgdat);
 void get_page_bootmem(unsigned long info, struct page *page,
 		      unsigned long type);
 void put_page_bootmem(struct page *page);
+
+/*
+ * Any memory allocated via the memblock allocator and not via the
+ * buddy will be marked reserved already in the memmap. For those
+ * pages, we can call this function to free it to buddy allocator.
+ */
+static inline void free_bootmem_page(struct page *page)
+{
+	unsigned long magic = (unsigned long)page->freelist;
+
+	/*
+	 * The reserve_bootmem_region sets the reserved flag on bootmem
+	 * pages.
+	 */
+	VM_BUG_ON_PAGE(page_ref_count(page) != 2, page);
+
+	if (magic == SECTION_INFO || magic == MIX_SECTION_INFO)
+		put_page_bootmem(page);
+	else
+		VM_BUG_ON_PAGE(1, page);
+}
 #else
 static inline void register_page_bootmem_info_node(struct pglist_data *pgdat)
 {
@@ -35,6 +56,11 @@ static inline void get_page_bootmem(unsigned long info, struct page *page,
 				    unsigned long type)
 {
 }
+
+static inline void free_bootmem_page(struct page *page)
+{
+	free_reserved_page(page);
+}
 #endif
 
 #endif /* __LINUX_BOOTMEM_INFO_H */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 25b9041f9925..a4d160ddb749 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3046,6 +3046,9 @@ static inline void print_vma_addr(char *prefix, unsigned long rip)
 }
 #endif
 
+void vmemmap_remap_free(unsigned long start, unsigned long end,
+			unsigned long reuse);
+
 void *sparse_buffer_alloc(unsigned long size);
 struct page * __populate_section_memmap(unsigned long pfn,
 		unsigned long nr_pages, int nid, struct vmem_altmap *altmap);
diff --git a/mm/Makefile b/mm/Makefile
index d0ccddae7a45..40ee404e200e 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -75,6 +75,7 @@ obj-$(CONFIG_FRONTSWAP)	+= frontswap.o
 obj-$(CONFIG_ZSWAP)	+= zswap.o
 obj-$(CONFIG_HAS_DMA)	+= dmapool.o
 obj-$(CONFIG_HUGETLBFS)	+= hugetlb.o
+obj-$(CONFIG_HUGETLB_PAGE_FREE_VMEMMAP)	+= hugetlb_vmemmap.o
 obj-$(CONFIG_NUMA) 	+= mempolicy.o
 obj-$(CONFIG_SPARSEMEM)	+= sparse.o
 obj-$(CONFIG_SPARSEMEM_VMEMMAP) += sparse-vmemmap.o
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 54d81d5947ed..923d05e2806b 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -41,6 +41,7 @@
 #include <linux/node.h>
 #include <linux/page_owner.h>
 #include "internal.h"
+#include "hugetlb_vmemmap.h"
 
 int hugetlb_max_hstate __read_mostly;
 unsigned int default_hstate_idx;
@@ -1485,6 +1486,7 @@ void free_huge_page(struct page *page)
 
 static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
 {
+	free_huge_page_vmemmap(h, page);
 	INIT_LIST_HEAD(&page->lru);
 	set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
 	hugetlb_set_page_subpool(page, NULL);
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
new file mode 100644
index 000000000000..e45a138a7f85
--- /dev/null
+++ b/mm/hugetlb_vmemmap.c
@@ -0,0 +1,218 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Free some vmemmap pages of HugeTLB
+ *
+ * Copyright (c) 2020, Bytedance. All rights reserved.
+ *
+ *     Author: Muchun Song <songmuchun@bytedance.com>
+ *
+ * The struct page structures (page structs) are used to describe a physical
+ * page frame. By default, there is a one-to-one mapping from a page frame to
+ * it's corresponding page struct.
+ *
+ * HugeTLB pages consist of multiple base page size pages and is supported by
+ * many architectures. See hugetlbpage.rst in the Documentation directory for
+ * more details. On the x86-64 architecture, HugeTLB pages of size 2MB and 1GB
+ * are currently supported. Since the base page size on x86 is 4KB, a 2MB
+ * HugeTLB page consists of 512 base pages and a 1GB HugeTLB page consists of
+ * 4096 base pages. For each base page, there is a corresponding page struct.
+ *
+ * Within the HugeTLB subsystem, only the first 4 page structs are used to
+ * contain unique information about a HugeTLB page. __NR_USED_SUBPAGE provides
+ * this upper limit. The only 'useful' information in the remaining page structs
+ * is the compound_head field, and this field is the same for all tail pages.
+ *
+ * By removing redundant page structs for HugeTLB pages, memory can be returned
+ * to the buddy allocator for other uses.
+ *
+ * Different architectures support different HugeTLB pages. For example, the
+ * following table is the HugeTLB page size supported by x86 and arm64
+ * architectures. Because arm64 supports 4k, 16k, and 64k base pages and
+ * supports contiguous entries, so it supports many kinds of sizes of HugeTLB
+ * page.
+ *
+ * +--------------+-----------+-----------------------------------------------+
+ * | Architecture | Page Size |                HugeTLB Page Size              |
+ * +--------------+-----------+-----------+-----------+-----------+-----------+
+ * |    x86-64    |    4KB    |    2MB    |    1GB    |           |           |
+ * +--------------+-----------+-----------+-----------+-----------+-----------+
+ * |              |    4KB    |   64KB    |    2MB    |    32MB   |    1GB    |
+ * |              +-----------+-----------+-----------+-----------+-----------+
+ * |    arm64     |   16KB    |    2MB    |   32MB    |     1GB   |           |
+ * |              +-----------+-----------+-----------+-----------+-----------+
+ * |              |   64KB    |    2MB    |  512MB    |    16GB   |           |
+ * +--------------+-----------+-----------+-----------+-----------+-----------+
+ *
+ * When the system boot up, every HugeTLB page has more than one struct page
+ * structs which size is (unit: pages):
+ *
+ *    struct_size = HugeTLB_Size / PAGE_SIZE * sizeof(struct page) / PAGE_SIZE
+ *
+ * Where HugeTLB_Size is the size of the HugeTLB page. We know that the size
+ * of the HugeTLB page is always n times PAGE_SIZE. So we can get the following
+ * relationship.
+ *
+ *    HugeTLB_Size = n * PAGE_SIZE
+ *
+ * Then,
+ *
+ *    struct_size = n * PAGE_SIZE / PAGE_SIZE * sizeof(struct page) / PAGE_SIZE
+ *                = n * sizeof(struct page) / PAGE_SIZE
+ *
+ * We can use huge mapping at the pud/pmd level for the HugeTLB page.
+ *
+ * For the HugeTLB page of the pmd level mapping, then
+ *
+ *    struct_size = n * sizeof(struct page) / PAGE_SIZE
+ *                = PAGE_SIZE / sizeof(pte_t) * sizeof(struct page) / PAGE_SIZE
+ *                = sizeof(struct page) / sizeof(pte_t)
+ *                = 64 / 8
+ *                = 8 (pages)
+ *
+ * Where n is how many pte entries which one page can contains. So the value of
+ * n is (PAGE_SIZE / sizeof(pte_t)).
+ *
+ * This optimization only supports 64-bit system, so the value of sizeof(pte_t)
+ * is 8. And this optimization also applicable only when the size of struct page
+ * is a power of two. In most cases, the size of struct page is 64 bytes (e.g.
+ * x86-64 and arm64). So if we use pmd level mapping for a HugeTLB page, the
+ * size of struct page structs of it is 8 page frames which size depends on the
+ * size of the base page.
+ *
+ * For the HugeTLB page of the pud level mapping, then
+ *
+ *    struct_size = PAGE_SIZE / sizeof(pmd_t) * struct_size(pmd)
+ *                = PAGE_SIZE / 8 * 8 (pages)
+ *                = PAGE_SIZE (pages)
+ *
+ * Where the struct_size(pmd) is the size of the struct page structs of a
+ * HugeTLB page of the pmd level mapping.
+ *
+ * E.g.: A 2MB HugeTLB page on x86_64 consists in 8 page frames while 1GB
+ * HugeTLB page consists in 4096.
+ *
+ * Next, we take the pmd level mapping of the HugeTLB page as an example to
+ * show the internal implementation of this optimization. There are 8 pages
+ * struct page structs associated with a HugeTLB page which is pmd mapped.
+ *
+ * Here is how things look before optimization.
+ *
+ *    HugeTLB                  struct pages(8 pages)         page frame(8 pages)
+ * +-----------+ ---virt_to_page---> +-----------+   mapping to   +-----------+
+ * |           |                     |     0     | -------------> |     0     |
+ * |           |                     +-----------+                +-----------+
+ * |           |                     |     1     | -------------> |     1     |
+ * |           |                     +-----------+                +-----------+
+ * |           |                     |     2     | -------------> |     2     |
+ * |           |                     +-----------+                +-----------+
+ * |           |                     |     3     | -------------> |     3     |
+ * |           |                     +-----------+                +-----------+
+ * |           |                     |     4     | -------------> |     4     |
+ * |    PMD    |                     +-----------+                +-----------+
+ * |   level   |                     |     5     | -------------> |     5     |
+ * |  mapping  |                     +-----------+                +-----------+
+ * |           |                     |     6     | -------------> |     6     |
+ * |           |                     +-----------+                +-----------+
+ * |           |                     |     7     | -------------> |     7     |
+ * |           |                     +-----------+                +-----------+
+ * |           |
+ * |           |
+ * |           |
+ * +-----------+
+ *
+ * The value of page->compound_head is the same for all tail pages. The first
+ * page of page structs (page 0) associated with the HugeTLB page contains the 4
+ * page structs necessary to describe the HugeTLB. The only use of the remaining
+ * pages of page structs (page 1 to page 7) is to point to page->compound_head.
+ * Therefore, we can remap pages 2 to 7 to page 1. Only 2 pages of page structs
+ * will be used for each HugeTLB page. This will allow us to free the remaining
+ * 6 pages to the buddy allocator.
+ *
+ * Here is how things look after remapping.
+ *
+ *    HugeTLB                  struct pages(8 pages)         page frame(8 pages)
+ * +-----------+ ---virt_to_page---> +-----------+   mapping to   +-----------+
+ * |           |                     |     0     | -------------> |     0     |
+ * |           |                     +-----------+                +-----------+
+ * |           |                     |     1     | -------------> |     1     |
+ * |           |                     +-----------+                +-----------+
+ * |           |                     |     2     | ----------------^ ^ ^ ^ ^ ^
+ * |           |                     +-----------+                   | | | | |
+ * |           |                     |     3     | ------------------+ | | | |
+ * |           |                     +-----------+                     | | | |
+ * |           |                     |     4     | --------------------+ | | |
+ * |    PMD    |                     +-----------+                       | | |
+ * |   level   |                     |     5     | ----------------------+ | |
+ * |  mapping  |                     +-----------+                         | |
+ * |           |                     |     6     | ------------------------+ |
+ * |           |                     +-----------+                           |
+ * |           |                     |     7     | --------------------------+
+ * |           |                     +-----------+
+ * |           |
+ * |           |
+ * |           |
+ * +-----------+
+ *
+ * When a HugeTLB is freed to the buddy system, we should allocate 6 pages for
+ * vmemmap pages and restore the previous mapping relationship.
+ *
+ * For the HugeTLB page of the pud level mapping. It is similar to the former.
+ * We also can use this approach to free (PAGE_SIZE - 2) vmemmap pages.
+ *
+ * Apart from the HugeTLB page of the pmd/pud level mapping, some architectures
+ * (e.g. aarch64) provides a contiguous bit in the translation table entries
+ * that hints to the MMU to indicate that it is one of a contiguous set of
+ * entries that can be cached in a single TLB entry.
+ *
+ * The contiguous bit is used to increase the mapping size at the pmd and pte
+ * (last) level. So this type of HugeTLB page can be optimized only when its
+ * size of the struct page structs is greater than 2 pages.
+ */
+#include "hugetlb_vmemmap.h"
+
+/*
+ * There are a lot of struct page structures associated with each HugeTLB page.
+ * For tail pages, the value of compound_head is the same. So we can reuse first
+ * page of tail page structures. We map the virtual addresses of the remaining
+ * pages of tail page structures to the first tail page struct, and then free
+ * these page frames. Therefore, we need to reserve two pages as vmemmap areas.
+ */
+#define RESERVE_VMEMMAP_NR		2U
+#define RESERVE_VMEMMAP_SIZE		(RESERVE_VMEMMAP_NR << PAGE_SHIFT)
+
+/*
+ * How many vmemmap pages associated with a HugeTLB page that can be freed
+ * to the buddy allocator.
+ *
+ * Todo: Returns zero for now, which means the feature is disabled. We will
+ * enable it once all the infrastructure is there.
+ */
+static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
+{
+	return 0;
+}
+
+static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
+{
+	return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
+}
+
+void free_huge_page_vmemmap(struct hstate *h, struct page *head)
+{
+	unsigned long vmemmap_addr = (unsigned long)head;
+	unsigned long vmemmap_end, vmemmap_reuse;
+
+	if (!free_vmemmap_pages_per_hpage(h))
+		return;
+
+	vmemmap_addr += RESERVE_VMEMMAP_SIZE;
+	vmemmap_end = vmemmap_addr + free_vmemmap_pages_size_per_hpage(h);
+	vmemmap_reuse = vmemmap_addr - PAGE_SIZE;
+
+	/*
+	 * Remap the vmemmap virtual address range [@vmemmap_addr, @vmemmap_end)
+	 * to the page which @vmemmap_reuse is mapped to, then free the pages
+	 * which the range [@vmemmap_addr, @vmemmap_end] is mapped to.
+	 */
+	vmemmap_remap_free(vmemmap_addr, vmemmap_end, vmemmap_reuse);
+}
diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
new file mode 100644
index 000000000000..6923f03534d5
--- /dev/null
+++ b/mm/hugetlb_vmemmap.h
@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Free some vmemmap pages of HugeTLB
+ *
+ * Copyright (c) 2020, Bytedance. All rights reserved.
+ *
+ *     Author: Muchun Song <songmuchun@bytedance.com>
+ */
+#ifndef _LINUX_HUGETLB_VMEMMAP_H
+#define _LINUX_HUGETLB_VMEMMAP_H
+#include <linux/hugetlb.h>
+
+#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+void free_huge_page_vmemmap(struct hstate *h, struct page *head);
+#else
+static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head)
+{
+}
+#endif /* CONFIG_HUGETLB_PAGE_FREE_VMEMMAP */
+#endif /* _LINUX_HUGETLB_VMEMMAP_H */
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index 16183d85a7d5..7d40b5bd7046 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -27,8 +27,202 @@
 #include <linux/spinlock.h>
 #include <linux/vmalloc.h>
 #include <linux/sched.h>
+#include <linux/pgtable.h>
+#include <linux/bootmem_info.h>
+
 #include <asm/dma.h>
 #include <asm/pgalloc.h>
+#include <asm/tlbflush.h>
+
+/**
+ * vmemmap_remap_walk - walk vmemmap page table
+ *
+ * @remap_pte:		called for each lowest-level entry (PTE).
+ * @reuse_page:		the page which is reused for the tail vmemmap pages.
+ * @reuse_addr:		the virtual address of the @reuse_page page.
+ * @vmemmap_pages:	the list head of the vmemmap pages that can be freed.
+ */
+struct vmemmap_remap_walk {
+	void (*remap_pte)(pte_t *pte, unsigned long addr,
+			  struct vmemmap_remap_walk *walk);
+	struct page *reuse_page;
+	unsigned long reuse_addr;
+	struct list_head *vmemmap_pages;
+};
+
+static void vmemmap_pte_range(pmd_t *pmd, unsigned long addr,
+			      unsigned long end,
+			      struct vmemmap_remap_walk *walk)
+{
+	pte_t *pte = pte_offset_kernel(pmd, addr);
+
+	/*
+	 * The reuse_page is found 'first' in table walk before we start
+	 * remapping (which is calling @walk->remap_pte).
+	 */
+	if (!walk->reuse_page) {
+		walk->reuse_page = pte_page(*pte);
+		/*
+		 * Because the reuse address is part of the range that we are
+		 * walking, skip the reuse address range.
+		 */
+		addr += PAGE_SIZE;
+		pte++;
+	}
+
+	for (; addr != end; addr += PAGE_SIZE, pte++)
+		walk->remap_pte(pte, addr, walk);
+}
+
+static void vmemmap_pmd_range(pud_t *pud, unsigned long addr,
+			      unsigned long end,
+			      struct vmemmap_remap_walk *walk)
+{
+	pmd_t *pmd;
+	unsigned long next;
+
+	pmd = pmd_offset(pud, addr);
+	do {
+		BUG_ON(pmd_leaf(*pmd));
+
+		next = pmd_addr_end(addr, end);
+		vmemmap_pte_range(pmd, addr, next, walk);
+	} while (pmd++, addr = next, addr != end);
+}
+
+static void vmemmap_pud_range(p4d_t *p4d, unsigned long addr,
+			      unsigned long end,
+			      struct vmemmap_remap_walk *walk)
+{
+	pud_t *pud;
+	unsigned long next;
+
+	pud = pud_offset(p4d, addr);
+	do {
+		next = pud_addr_end(addr, end);
+		vmemmap_pmd_range(pud, addr, next, walk);
+	} while (pud++, addr = next, addr != end);
+}
+
+static void vmemmap_p4d_range(pgd_t *pgd, unsigned long addr,
+			      unsigned long end,
+			      struct vmemmap_remap_walk *walk)
+{
+	p4d_t *p4d;
+	unsigned long next;
+
+	p4d = p4d_offset(pgd, addr);
+	do {
+		next = p4d_addr_end(addr, end);
+		vmemmap_pud_range(p4d, addr, next, walk);
+	} while (p4d++, addr = next, addr != end);
+}
+
+static void vmemmap_remap_range(unsigned long start, unsigned long end,
+				struct vmemmap_remap_walk *walk)
+{
+	unsigned long addr = start;
+	unsigned long next;
+	pgd_t *pgd;
+
+	VM_BUG_ON(!IS_ALIGNED(start, PAGE_SIZE));
+	VM_BUG_ON(!IS_ALIGNED(end, PAGE_SIZE));
+
+	pgd = pgd_offset_k(addr);
+	do {
+		next = pgd_addr_end(addr, end);
+		vmemmap_p4d_range(pgd, addr, next, walk);
+	} while (pgd++, addr = next, addr != end);
+
+	/*
+	 * We only change the mapping of the vmemmap virtual address range
+	 * [@start + PAGE_SIZE, end), so we only need to flush the TLB which
+	 * belongs to the range.
+	 */
+	flush_tlb_kernel_range(start + PAGE_SIZE, end);
+}
+
+/*
+ * Free a vmemmap page. A vmemmap page can be allocated from the memblock
+ * allocator or buddy allocator. If the PG_reserved flag is set, it means
+ * that it allocated from the memblock allocator, just free it via the
+ * free_bootmem_page(). Otherwise, use __free_page().
+ */
+static inline void free_vmemmap_page(struct page *page)
+{
+	if (PageReserved(page))
+		free_bootmem_page(page);
+	else
+		__free_page(page);
+}
+
+/* Free a list of the vmemmap pages */
+static void free_vmemmap_page_list(struct list_head *list)
+{
+	struct page *page, *next;
+
+	list_for_each_entry_safe(page, next, list, lru) {
+		list_del(&page->lru);
+		free_vmemmap_page(page);
+	}
+}
+
+static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
+			      struct vmemmap_remap_walk *walk)
+{
+	/*
+	 * Remap the tail pages as read-only to catch illegal write operation
+	 * to the tail pages.
+	 */
+	pgprot_t pgprot = PAGE_KERNEL_RO;
+	pte_t entry = mk_pte(walk->reuse_page, pgprot);
+	struct page *page = pte_page(*pte);
+
+	list_add(&page->lru, walk->vmemmap_pages);
+	set_pte_at(&init_mm, addr, pte, entry);
+}
+
+/**
+ * vmemmap_remap_free - remap the vmemmap virtual address range [@start, @end)
+ *			to the page which @reuse is mapped to, then free vmemmap
+ *			which the range are mapped to.
+ * @start:	start address of the vmemmap virtual address range that we want
+ *		to remap.
+ * @end:	end address of the vmemmap virtual address range that we want to
+ *		remap.
+ * @reuse:	reuse address.
+ *
+ * Note: This function depends on vmemmap being base page mapped. Please make
+ * sure that we disable PMD mapping of vmemmap pages when calling this function.
+ */
+void vmemmap_remap_free(unsigned long start, unsigned long end,
+			unsigned long reuse)
+{
+	LIST_HEAD(vmemmap_pages);
+	struct vmemmap_remap_walk walk = {
+		.remap_pte	= vmemmap_remap_pte,
+		.reuse_addr	= reuse,
+		.vmemmap_pages	= &vmemmap_pages,
+	};
+
+	/*
+	 * In order to make remapping routine most efficient for the huge pages,
+	 * the routine of vmemmap page table walking has the following rules
+	 * (see more details from the vmemmap_pte_range()):
+	 *
+	 * - The range [@start, @end) and the range [@reuse, @reuse + PAGE_SIZE)
+	 *   should be continuous.
+	 * - The @reuse address is part of the range [@reuse, @end) that we are
+	 *   walking which is passed to vmemmap_remap_range().
+	 * - The @reuse address is the first in the complete range.
+	 *
+	 * So we need to make sure that @start and @reuse meet the above rules.
+	 */
+	BUG_ON(start - reuse != PAGE_SIZE);
+
+	vmemmap_remap_range(reuse, end, &walk);
+	free_vmemmap_page_list(&vmemmap_pages);
+}
 
 /*
  * Allocate a block of memory to be used to back the virtual memory map
-- 
2.11.0


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [PATCH v20 5/9] mm: hugetlb: defer freeing of HugeTLB pages
  2021-04-15  8:39 [PATCH v20 0/9] Free some vmemmap pages of HugeTLB page Muchun Song
                   ` (3 preceding siblings ...)
  2021-04-15  8:40 ` [PATCH v20 4/9] mm: hugetlb: free the vmemmap pages associated with each HugeTLB page Muchun Song
@ 2021-04-15  8:40 ` Muchun Song
  2021-04-16 23:55   ` Mike Kravetz
  2021-04-15  8:40 ` [PATCH v20 6/9] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page Muchun Song
                   ` (3 subsequent siblings)
  8 siblings, 1 reply; 24+ messages in thread
From: Muchun Song @ 2021-04-15  8:40 UTC (permalink / raw)
  To: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, pawan.kumar.gupta, rdunlap,
	oneukum, anshuman.khandual, jroedel, almasrymina, rientjes,
	willy, osalvador, mhocko, song.bao.hua, david, naoya.horiguchi,
	joao.m.martins
  Cc: duanxiongchun, fam.zheng, linux-doc, linux-kernel, linux-mm,
	linux-fsdevel, Muchun Song

In the subsequent patch, we should allocate the vmemmap pages when
freeing a HugeTLB page. But update_and_free_page() can be called
under any context, so we cannot use GFP_KERNEL to allocate vmemmap
pages. However, we can defer the actual freeing in a kworker to
prevent from using GFP_ATOMIC to allocate the vmemmap pages.

The __update_and_free_page() is where the call to allocate vmemmmap
pages will be inserted.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/hugetlb.c         | 73 ++++++++++++++++++++++++++++++++++++++++++++++++----
 mm/hugetlb_vmemmap.c | 12 ---------
 mm/hugetlb_vmemmap.h | 17 ++++++++++++
 3 files changed, 85 insertions(+), 17 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 923d05e2806b..eeb8f5480170 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1376,7 +1376,7 @@ static void remove_hugetlb_page(struct hstate *h, struct page *page,
 	h->nr_huge_pages_node[nid]--;
 }
 
-static void update_and_free_page(struct hstate *h, struct page *page)
+static void __update_and_free_page(struct hstate *h, struct page *page)
 {
 	int i;
 	struct page *subpage = page;
@@ -1399,12 +1399,73 @@ static void update_and_free_page(struct hstate *h, struct page *page)
 	}
 }
 
+/*
+ * As update_and_free_page() can be called under any context, so we cannot
+ * use GFP_KERNEL to allocate vmemmap pages. However, we can defer the
+ * actual freeing in a workqueue to prevent from using GFP_ATOMIC to allocate
+ * the vmemmap pages.
+ *
+ * free_hpage_workfn() locklessly retrieves the linked list of pages to be
+ * freed and frees them one-by-one. As the page->mapping pointer is going
+ * to be cleared in free_hpage_workfn() anyway, it is reused as the llist_node
+ * structure of a lockless linked list of huge pages to be freed.
+ */
+static LLIST_HEAD(hpage_freelist);
+
+static void free_hpage_workfn(struct work_struct *work)
+{
+	struct llist_node *node;
+
+	node = llist_del_all(&hpage_freelist);
+
+	while (node) {
+		struct page *page;
+		struct hstate *h;
+
+		page = container_of((struct address_space **)node,
+				     struct page, mapping);
+		node = node->next;
+		page->mapping = NULL;
+		h = page_hstate(page);
+
+		__update_and_free_page(h, page);
+
+		cond_resched();
+	}
+}
+static DECLARE_WORK(free_hpage_work, free_hpage_workfn);
+
+static inline void flush_free_hpage_work(struct hstate *h)
+{
+	if (free_vmemmap_pages_per_hpage(h))
+		flush_work(&free_hpage_work);
+}
+
+static void update_and_free_page(struct hstate *h, struct page *page,
+				 bool atomic)
+{
+	if (!free_vmemmap_pages_per_hpage(h) || !atomic) {
+		__update_and_free_page(h, page);
+		return;
+	}
+
+	/*
+	 * Defer freeing to avoid using GFP_ATOMIC to allocate vmemmap pages.
+	 *
+	 * Only call schedule_work() if hpage_freelist is previously
+	 * empty. Otherwise, schedule_work() had been called but the workfn
+	 * hasn't retrieved the list yet.
+	 */
+	if (llist_add((struct llist_node *)&page->mapping, &hpage_freelist))
+		schedule_work(&free_hpage_work);
+}
+
 static void update_and_free_pages_bulk(struct hstate *h, struct list_head *list)
 {
 	struct page *page, *t_page;
 
 	list_for_each_entry_safe(page, t_page, list, lru) {
-		update_and_free_page(h, page);
+		update_and_free_page(h, page, false);
 		cond_resched();
 	}
 }
@@ -1471,12 +1532,12 @@ void free_huge_page(struct page *page)
 	if (HPageTemporary(page)) {
 		remove_hugetlb_page(h, page, false);
 		spin_unlock_irqrestore(&hugetlb_lock, flags);
-		update_and_free_page(h, page);
+		update_and_free_page(h, page, true);
 	} else if (h->surplus_huge_pages_node[nid]) {
 		/* remove the page from active list */
 		remove_hugetlb_page(h, page, true);
 		spin_unlock_irqrestore(&hugetlb_lock, flags);
-		update_and_free_page(h, page);
+		update_and_free_page(h, page, true);
 	} else {
 		arch_clear_hugepage_flags(page);
 		enqueue_huge_page(h, page);
@@ -1785,7 +1846,7 @@ int dissolve_free_huge_page(struct page *page)
 		remove_hugetlb_page(h, page, false);
 		h->max_huge_pages--;
 		spin_unlock_irq(&hugetlb_lock);
-		update_and_free_page(h, head);
+		update_and_free_page(h, head, false);
 		return 0;
 	}
 out:
@@ -2627,6 +2688,7 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
 	 * pages in hstate via the proc/sysfs interfaces.
 	 */
 	mutex_lock(&h->resize_lock);
+	flush_free_hpage_work(h);
 	spin_lock_irq(&hugetlb_lock);
 
 	/*
@@ -2736,6 +2798,7 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
 	/* free the pages after dropping lock */
 	spin_unlock_irq(&hugetlb_lock);
 	update_and_free_pages_bulk(h, &page_list);
+	flush_free_hpage_work(h);
 	spin_lock_irq(&hugetlb_lock);
 
 	while (count < persistent_huge_pages(h)) {
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index e45a138a7f85..cb28c5b6c9ff 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -180,18 +180,6 @@
 #define RESERVE_VMEMMAP_NR		2U
 #define RESERVE_VMEMMAP_SIZE		(RESERVE_VMEMMAP_NR << PAGE_SHIFT)
 
-/*
- * How many vmemmap pages associated with a HugeTLB page that can be freed
- * to the buddy allocator.
- *
- * Todo: Returns zero for now, which means the feature is disabled. We will
- * enable it once all the infrastructure is there.
- */
-static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
-{
-	return 0;
-}
-
 static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
 {
 	return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
index 6923f03534d5..01f8637adbe0 100644
--- a/mm/hugetlb_vmemmap.h
+++ b/mm/hugetlb_vmemmap.h
@@ -12,9 +12,26 @@
 
 #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
 void free_huge_page_vmemmap(struct hstate *h, struct page *head);
+
+/*
+ * How many vmemmap pages associated with a HugeTLB page that can be freed
+ * to the buddy allocator.
+ *
+ * Todo: Returns zero for now, which means the feature is disabled. We will
+ * enable it once all the infrastructure is there.
+ */
+static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
+{
+	return 0;
+}
 #else
 static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 {
 }
+
+static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
+{
+	return 0;
+}
 #endif /* CONFIG_HUGETLB_PAGE_FREE_VMEMMAP */
 #endif /* _LINUX_HUGETLB_VMEMMAP_H */
-- 
2.11.0


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [PATCH v20 6/9] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-04-15  8:39 [PATCH v20 0/9] Free some vmemmap pages of HugeTLB page Muchun Song
                   ` (4 preceding siblings ...)
  2021-04-15  8:40 ` [PATCH v20 5/9] mm: hugetlb: defer freeing of HugeTLB pages Muchun Song
@ 2021-04-15  8:40 ` Muchun Song
  2021-04-19 23:19   ` Mike Kravetz
  2021-04-15  8:40 ` [PATCH v20 7/9] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap Muchun Song
                   ` (2 subsequent siblings)
  8 siblings, 1 reply; 24+ messages in thread
From: Muchun Song @ 2021-04-15  8:40 UTC (permalink / raw)
  To: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, pawan.kumar.gupta, rdunlap,
	oneukum, anshuman.khandual, jroedel, almasrymina, rientjes,
	willy, osalvador, mhocko, song.bao.hua, david, naoya.horiguchi,
	joao.m.martins
  Cc: duanxiongchun, fam.zheng, linux-doc, linux-kernel, linux-mm,
	linux-fsdevel, Muchun Song

When we free a HugeTLB page to the buddy allocator, we need to allocate
the vmemmap pages associated with it. However, we may not be able to
allocate the vmemmap pages when the system is under memory pressure. In
this case, we just refuse to free the HugeTLB page. This changes behavior
in some corner cases as listed below:

 1) Failing to free a huge page triggered by the user (decrease nr_pages).

    User needs to try again later.

 2) Failing to free a surplus huge page when freed by the application.

    Try again later when freeing a huge page next time.

 3) Failing to dissolve a free huge page on ZONE_MOVABLE via
    offline_pages().

    This can happen when we have plenty of ZONE_MOVABLE memory, but
    not enough kernel memory to allocate vmemmmap pages.  We may even
    be able to migrate huge page contents, but will not be able to
    dissolve the source huge page.  This will prevent an offline
    operation and is unfortunate as memory offlining is expected to
    succeed on movable zones.  Users that depend on memory hotplug
    to succeed for movable zones should carefully consider whether the
    memory savings gained from this feature are worth the risk of
    possibly not being able to offline memory in certain situations.

 4) Failing to dissolve a huge page on CMA/ZONE_MOVABLE via
    alloc_contig_range() - once we have that handling in place. Mainly
    affects CMA and virtio-mem.

    Similar to 3). virito-mem will handle migration errors gracefully.
    CMA might be able to fallback on other free areas within the CMA
    region.

Vmemmap pages are allocated from the page freeing context. In order for
those allocations to be not disruptive (e.g. trigger oom killer)
__GFP_NORETRY is used. hugetlb_lock is dropped for the allocation
because a non sleeping allocation would be too fragile and it could fail
too easily under memory pressure. GFP_ATOMIC or other modes to access
memory reserves is not used because we want to prevent consuming
reserves under heavy hugetlb freeing.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 Documentation/admin-guide/mm/hugetlbpage.rst    |  8 +++
 Documentation/admin-guide/mm/memory-hotplug.rst | 13 ++++
 include/linux/hugetlb.h                         |  3 +
 include/linux/mm.h                              |  2 +
 mm/hugetlb.c                                    | 85 ++++++++++++++++++++-----
 mm/hugetlb_vmemmap.c                            | 34 ++++++++++
 mm/hugetlb_vmemmap.h                            |  6 ++
 mm/sparse-vmemmap.c                             | 75 +++++++++++++++++++++-
 8 files changed, 210 insertions(+), 16 deletions(-)

diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst
index f7b1c7462991..6988895d09a8 100644
--- a/Documentation/admin-guide/mm/hugetlbpage.rst
+++ b/Documentation/admin-guide/mm/hugetlbpage.rst
@@ -60,6 +60,10 @@ HugePages_Surp
         the pool above the value in ``/proc/sys/vm/nr_hugepages``. The
         maximum number of surplus huge pages is controlled by
         ``/proc/sys/vm/nr_overcommit_hugepages``.
+	Note: When the feature of freeing unused vmemmap pages associated
+	with each hugetlb page is enabled, the number of surplus huge pages
+	may be temporarily larger than the maximum number of surplus huge
+	pages when the system is under memory pressure.
 Hugepagesize
 	is the default hugepage size (in Kb).
 Hugetlb
@@ -80,6 +84,10 @@ returned to the huge page pool when freed by a task.  A user with root
 privileges can dynamically allocate more or free some persistent huge pages
 by increasing or decreasing the value of ``nr_hugepages``.
 
+Note: When the feature of freeing unused vmemmap pages associated with each
+hugetlb page is enabled, we can fail to free the huge pages triggered by
+the user when ths system is under memory pressure.  Please try again later.
+
 Pages that are used as huge pages are reserved inside the kernel and cannot
 be used for other purposes.  Huge pages cannot be swapped out under
 memory pressure.
diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
index 05d51d2d8beb..c6bae2d77160 100644
--- a/Documentation/admin-guide/mm/memory-hotplug.rst
+++ b/Documentation/admin-guide/mm/memory-hotplug.rst
@@ -357,6 +357,19 @@ creates ZONE_MOVABLE as following.
    Unfortunately, there is no information to show which memory block belongs
    to ZONE_MOVABLE. This is TBD.
 
+   Memory offlining can fail when dissolving a free huge page on ZONE_MOVABLE
+   and the feature of freeing unused vmemmap pages associated with each hugetlb
+   page is enabled.
+
+   This can happen when we have plenty of ZONE_MOVABLE memory, but not enough
+   kernel memory to allocate vmemmmap pages.  We may even be able to migrate
+   huge page contents, but will not be able to dissolve the source huge page.
+   This will prevent an offline operation and is unfortunate as memory offlining
+   is expected to succeed on movable zones.  Users that depend on memory hotplug
+   to succeed for movable zones should carefully consider whether the memory
+   savings gained from this feature are worth the risk of possibly not being
+   able to offline memory in certain situations.
+
 .. note::
    Techniques that rely on long-term pinnings of memory (especially, RDMA and
    vfio) are fundamentally problematic with ZONE_MOVABLE and, therefore, memory
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 0abed7e766b8..6e970a7d3480 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -525,6 +525,7 @@ unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
  *	code knows it has only reference.  All other examinations and
  *	modifications require hugetlb_lock.
  * HPG_freed - Set when page is on the free lists.
+ * HPG_vmemmap_optimized - Set when the vmemmap pages of the page are freed.
  *	Synchronization: hugetlb_lock held for examination and modification.
  */
 enum hugetlb_page_flags {
@@ -532,6 +533,7 @@ enum hugetlb_page_flags {
 	HPG_migratable,
 	HPG_temporary,
 	HPG_freed,
+	HPG_vmemmap_optimized,
 	__NR_HPAGEFLAGS,
 };
 
@@ -577,6 +579,7 @@ HPAGEFLAG(RestoreReserve, restore_reserve)
 HPAGEFLAG(Migratable, migratable)
 HPAGEFLAG(Temporary, temporary)
 HPAGEFLAG(Freed, freed)
+HPAGEFLAG(VmemmapOptimized, vmemmap_optimized)
 
 #ifdef CONFIG_HUGETLB_PAGE
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a4d160ddb749..d0854828bb9c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3048,6 +3048,8 @@ static inline void print_vma_addr(char *prefix, unsigned long rip)
 
 void vmemmap_remap_free(unsigned long start, unsigned long end,
 			unsigned long reuse);
+int vmemmap_remap_alloc(unsigned long start, unsigned long end,
+			unsigned long reuse, gfp_t gfp_mask);
 
 void *sparse_buffer_alloc(unsigned long size);
 struct page * __populate_section_memmap(unsigned long pfn,
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index eeb8f5480170..1c37f0098e00 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1376,6 +1376,34 @@ static void remove_hugetlb_page(struct hstate *h, struct page *page,
 	h->nr_huge_pages_node[nid]--;
 }
 
+static void add_hugetlb_page(struct hstate *h, struct page *page,
+			     bool adjust_surplus)
+{
+	int nid = page_to_nid(page);
+
+	lockdep_assert_held(&hugetlb_lock);
+
+	INIT_LIST_HEAD(&page->lru);
+	h->nr_huge_pages++;
+	h->nr_huge_pages_node[nid]++;
+
+	if (adjust_surplus) {
+		h->surplus_huge_pages++;
+		h->surplus_huge_pages_node[nid]++;
+	}
+
+	set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
+
+	/*
+	 * The refcount can possibly be increased by memory-failure or
+	 * soft_offline handlers.
+	 */
+	if (likely(put_page_testzero(page))) {
+		arch_clear_hugepage_flags(page);
+		enqueue_huge_page(h, page);
+	}
+}
+
 static void __update_and_free_page(struct hstate *h, struct page *page)
 {
 	int i;
@@ -1384,6 +1412,18 @@ static void __update_and_free_page(struct hstate *h, struct page *page)
 	if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
 		return;
 
+	if (alloc_huge_page_vmemmap(h, page)) {
+		spin_lock_irq(&hugetlb_lock);
+		/*
+		 * If we cannot allocate vmemmap pages, just refuse to free the
+		 * page and put the page back on the hugetlb free list and treat
+		 * as a surplus page.
+		 */
+		add_hugetlb_page(h, page, true);
+		spin_unlock_irq(&hugetlb_lock);
+		return;
+	}
+
 	for (i = 0; i < pages_per_huge_page(h);
 	     i++, subpage = mem_map_next(subpage, page, i)) {
 		subpage->flags &= ~(1 << PG_locked | 1 << PG_error |
@@ -1444,7 +1484,7 @@ static inline void flush_free_hpage_work(struct hstate *h)
 static void update_and_free_page(struct hstate *h, struct page *page,
 				 bool atomic)
 {
-	if (!free_vmemmap_pages_per_hpage(h) || !atomic) {
+	if (!HPageVmemmapOptimized(page) || !atomic) {
 		__update_and_free_page(h, page);
 		return;
 	}
@@ -1790,10 +1830,14 @@ static struct page *remove_pool_huge_page(struct hstate *h,
  * nothing for in-use hugepages and non-hugepages.
  * This function returns values like below:
  *
- *  -EBUSY: failed to dissolved free hugepages or the hugepage is in-use
- *          (allocated or reserved.)
- *       0: successfully dissolved free hugepages or the page is not a
- *          hugepage (considered as already dissolved)
+ *  -ENOMEM: failed to allocate vmemmap pages to free the freed hugepages
+ *           when the system is under memory pressure and the feature of
+ *           freeing unused vmemmap pages associated with each hugetlb page
+ *           is enabled.
+ *  -EBUSY:  failed to dissolved free hugepages or the hugepage is in-use
+ *           (allocated or reserved.)
+ *       0:  successfully dissolved free hugepages or the page is not a
+ *           hugepage (considered as already dissolved)
  */
 int dissolve_free_huge_page(struct page *page)
 {
@@ -1835,19 +1879,30 @@ int dissolve_free_huge_page(struct page *page)
 			goto retry;
 		}
 
-		/*
-		 * Move PageHWPoison flag from head page to the raw error page,
-		 * which makes any subpages rather than the error page reusable.
-		 */
-		if (PageHWPoison(head) && page != head) {
-			SetPageHWPoison(page);
-			ClearPageHWPoison(head);
-		}
 		remove_hugetlb_page(h, page, false);
 		h->max_huge_pages--;
 		spin_unlock_irq(&hugetlb_lock);
-		update_and_free_page(h, head, false);
-		return 0;
+
+		rc = alloc_huge_page_vmemmap(h, page);
+		if (!rc) {
+			/*
+			 * Move PageHWPoison flag from head page to the raw
+			 * error page, which makes any subpages rather than
+			 * the error page reusable.
+			 */
+			if (PageHWPoison(head) && page != head) {
+				SetPageHWPoison(page);
+				ClearPageHWPoison(head);
+			}
+			update_and_free_page(h, head, false);
+		} else {
+			spin_lock_irq(&hugetlb_lock);
+			add_hugetlb_page(h, page, false);
+			h->max_huge_pages++;
+			spin_unlock_irq(&hugetlb_lock);
+		}
+
+		return rc;
 	}
 out:
 	spin_unlock_irq(&hugetlb_lock);
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index cb28c5b6c9ff..a897c7778246 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -185,6 +185,38 @@ static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
 	return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
 }
 
+/*
+ * Previously discarded vmemmap pages will be allocated and remapping
+ * after this function returns zero.
+ */
+int alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
+{
+	int ret;
+	unsigned long vmemmap_addr = (unsigned long)head;
+	unsigned long vmemmap_end, vmemmap_reuse;
+
+	if (!HPageVmemmapOptimized(head))
+		return 0;
+
+	vmemmap_addr += RESERVE_VMEMMAP_SIZE;
+	vmemmap_end = vmemmap_addr + free_vmemmap_pages_size_per_hpage(h);
+	vmemmap_reuse = vmemmap_addr - PAGE_SIZE;
+	/*
+	 * The pages which the vmemmap virtual address range [@vmemmap_addr,
+	 * @vmemmap_end) are mapped to are freed to the buddy allocator, and
+	 * the range is mapped to the page which @vmemmap_reuse is mapped to.
+	 * When a HugeTLB page is freed to the buddy allocator, previously
+	 * discarded vmemmap pages must be allocated and remapping.
+	 */
+	ret = vmemmap_remap_alloc(vmemmap_addr, vmemmap_end, vmemmap_reuse,
+				  GFP_KERNEL | __GFP_NORETRY | __GFP_THISNODE);
+
+	if (!ret)
+		ClearHPageVmemmapOptimized(head);
+
+	return ret;
+}
+
 void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 {
 	unsigned long vmemmap_addr = (unsigned long)head;
@@ -203,4 +235,6 @@ void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 	 * which the range [@vmemmap_addr, @vmemmap_end] is mapped to.
 	 */
 	vmemmap_remap_free(vmemmap_addr, vmemmap_end, vmemmap_reuse);
+
+	SetHPageVmemmapOptimized(head);
 }
diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
index 01f8637adbe0..a37771b0b82a 100644
--- a/mm/hugetlb_vmemmap.h
+++ b/mm/hugetlb_vmemmap.h
@@ -11,6 +11,7 @@
 #include <linux/hugetlb.h>
 
 #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+int alloc_huge_page_vmemmap(struct hstate *h, struct page *head);
 void free_huge_page_vmemmap(struct hstate *h, struct page *head);
 
 /*
@@ -25,6 +26,11 @@ static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
 	return 0;
 }
 #else
+static inline int alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
+{
+	return 0;
+}
+
 static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 {
 }
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index 7d40b5bd7046..693de0aec7a8 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -40,7 +40,8 @@
  * @remap_pte:		called for each lowest-level entry (PTE).
  * @reuse_page:		the page which is reused for the tail vmemmap pages.
  * @reuse_addr:		the virtual address of the @reuse_page page.
- * @vmemmap_pages:	the list head of the vmemmap pages that can be freed.
+ * @vmemmap_pages:	the list head of the vmemmap pages that can be freed
+ *			or is mapped from.
  */
 struct vmemmap_remap_walk {
 	void (*remap_pte)(pte_t *pte, unsigned long addr,
@@ -224,6 +225,78 @@ void vmemmap_remap_free(unsigned long start, unsigned long end,
 	free_vmemmap_page_list(&vmemmap_pages);
 }
 
+static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
+				struct vmemmap_remap_walk *walk)
+{
+	pgprot_t pgprot = PAGE_KERNEL;
+	struct page *page;
+	void *to;
+
+	BUG_ON(pte_page(*pte) != walk->reuse_page);
+
+	page = list_first_entry(walk->vmemmap_pages, struct page, lru);
+	list_del(&page->lru);
+	to = page_to_virt(page);
+	copy_page(to, (void *)walk->reuse_addr);
+
+	set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot));
+}
+
+static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
+				   gfp_t gfp_mask, struct list_head *list)
+{
+	unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
+	int nid = page_to_nid((struct page *)start);
+	struct page *page, *next;
+
+	while (nr_pages--) {
+		page = alloc_pages_node(nid, gfp_mask, 0);
+		if (!page)
+			goto out;
+		list_add_tail(&page->lru, list);
+	}
+
+	return 0;
+out:
+	list_for_each_entry_safe(page, next, list, lru)
+		__free_pages(page, 0);
+	return -ENOMEM;
+}
+
+/**
+ * vmemmap_remap_alloc - remap the vmemmap virtual address range [@start, end)
+ *			 to the page which is from the @vmemmap_pages
+ *			 respectively.
+ * @start:	start address of the vmemmap virtual address range that we want
+ *		to remap.
+ * @end:	end address of the vmemmap virtual address range that we want to
+ *		remap.
+ * @reuse:	reuse address.
+ * @gpf_mask:	GFP flag for allocating vmemmap pages.
+ */
+int vmemmap_remap_alloc(unsigned long start, unsigned long end,
+			unsigned long reuse, gfp_t gfp_mask)
+{
+	LIST_HEAD(vmemmap_pages);
+	struct vmemmap_remap_walk walk = {
+		.remap_pte	= vmemmap_restore_pte,
+		.reuse_addr	= reuse,
+		.vmemmap_pages	= &vmemmap_pages,
+	};
+
+	/* See the comment in the vmemmap_remap_free(). */
+	BUG_ON(start - reuse != PAGE_SIZE);
+
+	might_sleep_if(gfpflags_allow_blocking(gfp_mask));
+
+	if (alloc_vmemmap_page_list(start, end, gfp_mask, &vmemmap_pages))
+		return -ENOMEM;
+
+	vmemmap_remap_range(reuse, end, &walk);
+
+	return 0;
+}
+
 /*
  * Allocate a block of memory to be used to back the virtual memory map
  * or to back the page tables that are used to create the mapping.
-- 
2.11.0


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [PATCH v20 7/9] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap
  2021-04-15  8:39 [PATCH v20 0/9] Free some vmemmap pages of HugeTLB page Muchun Song
                   ` (5 preceding siblings ...)
  2021-04-15  8:40 ` [PATCH v20 6/9] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page Muchun Song
@ 2021-04-15  8:40 ` Muchun Song
  2021-04-19 23:41   ` Mike Kravetz
  2021-04-15  8:40 ` [PATCH v20 8/9] mm: memory_hotplug: disable memmap_on_memory when hugetlb_free_vmemmap enabled Muchun Song
  2021-04-15  8:40 ` [PATCH v20 9/9] mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate Muchun Song
  8 siblings, 1 reply; 24+ messages in thread
From: Muchun Song @ 2021-04-15  8:40 UTC (permalink / raw)
  To: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, pawan.kumar.gupta, rdunlap,
	oneukum, anshuman.khandual, jroedel, almasrymina, rientjes,
	willy, osalvador, mhocko, song.bao.hua, david, naoya.horiguchi,
	joao.m.martins
  Cc: duanxiongchun, fam.zheng, linux-doc, linux-kernel, linux-mm,
	linux-fsdevel, Muchun Song, Miaohe Lin, Chen Huang,
	Bodeddula Balasubramaniam

Add a kernel parameter hugetlb_free_vmemmap to enable the feature of
freeing unused vmemmap pages associated with each hugetlb page on boot.

We disables PMD mapping of vmemmap pages for x86-64 arch when this
feature is enabled. Because vmemmap_remap_free() depends on vmemmap
being base page mapped.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Barry Song <song.bao.hua@hisilicon.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Tested-by: Chen Huang <chenhuang5@huawei.com>
Tested-by: Bodeddula Balasubramaniam <bodeddub@amazon.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 17 +++++++++++++++++
 Documentation/admin-guide/mm/hugetlbpage.rst    |  3 +++
 arch/x86/mm/init_64.c                           |  8 ++++++--
 include/linux/hugetlb.h                         | 19 +++++++++++++++++++
 mm/hugetlb_vmemmap.c                            | 24 ++++++++++++++++++++++++
 5 files changed, 69 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 3bf052d14504..9e655f5206ac 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1611,6 +1611,23 @@
 			Documentation/admin-guide/mm/hugetlbpage.rst.
 			Format: size[KMG]
 
+	hugetlb_free_vmemmap=
+			[KNL] Reguires CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+			enabled.
+			Allows heavy hugetlb users to free up some more
+			memory (6 * PAGE_SIZE for each 2MB hugetlb page).
+			This feauture is not free though. Large page
+			tables are not used to back vmemmap pages which
+			can lead to a performance degradation for some
+			workloads. Also there will be memory allocation
+			required when hugetlb pages are freed from the
+			pool which can lead to corner cases under heavy
+			memory pressure.
+			Format: { on | off (default) }
+
+			on:  enable the feature
+			off: disable the feature
+
 	hung_task_panic=
 			[KNL] Should the hung task detector generate panics.
 			Format: 0 | 1
diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst
index 6988895d09a8..8abaeb144e44 100644
--- a/Documentation/admin-guide/mm/hugetlbpage.rst
+++ b/Documentation/admin-guide/mm/hugetlbpage.rst
@@ -153,6 +153,9 @@ default_hugepagesz
 
 	will all result in 256 2M huge pages being allocated.  Valid default
 	huge page size is architecture dependent.
+hugetlb_free_vmemmap
+	When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set, this enables freeing
+	unused vmemmap pages associated with each HugeTLB page.
 
 When multiple huge page sizes are supported, ``/proc/sys/vm/nr_hugepages``
 indicates the current number of pre-allocated huge pages of the default size.
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 65ea58527176..9d9d18d0c2a1 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -34,6 +34,7 @@
 #include <linux/gfp.h>
 #include <linux/kcore.h>
 #include <linux/bootmem_info.h>
+#include <linux/hugetlb.h>
 
 #include <asm/processor.h>
 #include <asm/bios_ebda.h>
@@ -1609,7 +1610,8 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 	VM_BUG_ON(!IS_ALIGNED(start, PAGE_SIZE));
 	VM_BUG_ON(!IS_ALIGNED(end, PAGE_SIZE));
 
-	if (end - start < PAGES_PER_SECTION * sizeof(struct page))
+	if ((is_hugetlb_free_vmemmap_enabled()  && !altmap) ||
+	    end - start < PAGES_PER_SECTION * sizeof(struct page))
 		err = vmemmap_populate_basepages(start, end, node, NULL);
 	else if (boot_cpu_has(X86_FEATURE_PSE))
 		err = vmemmap_populate_hugepages(start, end, node, altmap);
@@ -1637,6 +1639,8 @@ void register_page_bootmem_memmap(unsigned long section_nr,
 	pmd_t *pmd;
 	unsigned int nr_pmd_pages;
 	struct page *page;
+	bool base_mapping = !boot_cpu_has(X86_FEATURE_PSE) ||
+			    is_hugetlb_free_vmemmap_enabled();
 
 	for (; addr < end; addr = next) {
 		pte_t *pte = NULL;
@@ -1662,7 +1666,7 @@ void register_page_bootmem_memmap(unsigned long section_nr,
 		}
 		get_page_bootmem(section_nr, pud_page(*pud), MIX_SECTION_INFO);
 
-		if (!boot_cpu_has(X86_FEATURE_PSE)) {
+		if (base_mapping) {
 			next = (addr + PAGE_SIZE) & PAGE_MASK;
 			pmd = pmd_offset(pud, addr);
 			if (pmd_none(*pmd))
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 6e970a7d3480..4015cedacf91 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -894,6 +894,20 @@ static inline void huge_ptep_modify_prot_commit(struct vm_area_struct *vma,
 }
 #endif
 
+#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+extern bool hugetlb_free_vmemmap_enabled;
+
+static inline bool is_hugetlb_free_vmemmap_enabled(void)
+{
+	return hugetlb_free_vmemmap_enabled;
+}
+#else
+static inline bool is_hugetlb_free_vmemmap_enabled(void)
+{
+	return false;
+}
+#endif
+
 #else	/* CONFIG_HUGETLB_PAGE */
 struct hstate {};
 
@@ -1047,6 +1061,11 @@ static inline void set_huge_swap_pte_at(struct mm_struct *mm, unsigned long addr
 					pte_t *ptep, pte_t pte, unsigned long sz)
 {
 }
+
+static inline bool is_hugetlb_free_vmemmap_enabled(void)
+{
+	return false;
+}
 #endif	/* CONFIG_HUGETLB_PAGE */
 
 static inline spinlock_t *huge_pte_lock(struct hstate *h,
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index a897c7778246..3070e1465b1b 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -168,6 +168,8 @@
  * (last) level. So this type of HugeTLB page can be optimized only when its
  * size of the struct page structs is greater than 2 pages.
  */
+#define pr_fmt(fmt)	"HugeTLB: " fmt
+
 #include "hugetlb_vmemmap.h"
 
 /*
@@ -180,6 +182,28 @@
 #define RESERVE_VMEMMAP_NR		2U
 #define RESERVE_VMEMMAP_SIZE		(RESERVE_VMEMMAP_NR << PAGE_SHIFT)
 
+bool hugetlb_free_vmemmap_enabled;
+
+static int __init early_hugetlb_free_vmemmap_param(char *buf)
+{
+	/* We cannot optimize if a "struct page" crosses page boundaries. */
+	if ((!is_power_of_2(sizeof(struct page)))) {
+		pr_warn("cannot free vmemmap pages because \"struct page\" crosses page boundaries\n");
+		return 0;
+	}
+
+	if (!buf)
+		return -EINVAL;
+
+	if (!strcmp(buf, "on"))
+		hugetlb_free_vmemmap_enabled = true;
+	else if (strcmp(buf, "off"))
+		return -EINVAL;
+
+	return 0;
+}
+early_param("hugetlb_free_vmemmap", early_hugetlb_free_vmemmap_param);
+
 static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
 {
 	return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
-- 
2.11.0


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [PATCH v20 8/9] mm: memory_hotplug: disable memmap_on_memory when hugetlb_free_vmemmap enabled
  2021-04-15  8:39 [PATCH v20 0/9] Free some vmemmap pages of HugeTLB page Muchun Song
                   ` (6 preceding siblings ...)
  2021-04-15  8:40 ` [PATCH v20 7/9] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap Muchun Song
@ 2021-04-15  8:40 ` Muchun Song
  2021-04-20 10:35   ` Oscar Salvador
  2021-04-15  8:40 ` [PATCH v20 9/9] mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate Muchun Song
  8 siblings, 1 reply; 24+ messages in thread
From: Muchun Song @ 2021-04-15  8:40 UTC (permalink / raw)
  To: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, pawan.kumar.gupta, rdunlap,
	oneukum, anshuman.khandual, jroedel, almasrymina, rientjes,
	willy, osalvador, mhocko, song.bao.hua, david, naoya.horiguchi,
	joao.m.martins
  Cc: duanxiongchun, fam.zheng, linux-doc, linux-kernel, linux-mm,
	linux-fsdevel, Muchun Song

The parameter of memory_hotplug.memmap_on_memory is not compatible with
hugetlb_free_vmemmap. So disable it when hugetlb_free_vmemmap is
enabled.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 Documentation/admin-guide/kernel-parameters.txt |  4 ++++
 drivers/acpi/acpi_memhotplug.c                  |  1 +
 mm/memory_hotplug.c                             | 18 +++++++++++++-----
 3 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 9e655f5206ac..1f648b3e6120 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2893,6 +2893,10 @@
 			Note that even when enabled, there are a few cases where
 			the feature is not effective.
 
+			This is not compatible with hugetlb_free_vmemmap. If
+			both parameters are enabled, hugetlb_free_vmemmap takes
+			precedence over memory_hotplug.memmap_on_memory.
+
 	memtest=	[KNL,X86,ARM,PPC,RISCV] Enable memtest
 			Format: <integer>
 			default : 0 <disable>
diff --git a/drivers/acpi/acpi_memhotplug.c b/drivers/acpi/acpi_memhotplug.c
index 8cc195c4c861..0d7f595ee441 100644
--- a/drivers/acpi/acpi_memhotplug.c
+++ b/drivers/acpi/acpi_memhotplug.c
@@ -15,6 +15,7 @@
 #include <linux/acpi.h>
 #include <linux/memory.h>
 #include <linux/memory_hotplug.h>
+#include <linux/hugetlb.h>
 
 #include "internal.h"
 
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 68923c19bdea..c45ed6c0cd9f 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -981,6 +981,7 @@ static int online_memory_block(struct memory_block *mem, void *arg)
 
 bool mhp_supports_memmap_on_memory(unsigned long size)
 {
+	bool supported;
 	unsigned long nr_vmemmap_pages = size / PAGE_SIZE;
 	unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page);
 	unsigned long remaining_size = size - vmemmap_size;
@@ -1011,11 +1012,18 @@ bool mhp_supports_memmap_on_memory(unsigned long size)
 	 *	 altmap as an alternative source of memory, and we do not exactly
 	 *	 populate a single PMD.
 	 */
-	return memmap_on_memory &&
-	       IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) &&
-	       size == memory_block_size_bytes() &&
-	       IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
-	       IS_ALIGNED(remaining_size, pageblock_nr_pages << PAGE_SHIFT);
+	supported = memmap_on_memory &&
+		    IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) &&
+		    size == memory_block_size_bytes() &&
+		    IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
+		    IS_ALIGNED(remaining_size, pageblock_nr_pages << PAGE_SHIFT);
+
+	if (supported && is_hugetlb_free_vmemmap_enabled()) {
+		pr_info("Cannot enable memory_hotplug.memmap_on_memory, it is not compatible with hugetlb_free_vmemmap\n");
+		supported = false;
+	}
+
+	return supported;
 }
 
 /*
-- 
2.11.0


^ permalink raw reply	[flat|nested] 24+ messages in thread

* [PATCH v20 9/9] mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate
  2021-04-15  8:39 [PATCH v20 0/9] Free some vmemmap pages of HugeTLB page Muchun Song
                   ` (7 preceding siblings ...)
  2021-04-15  8:40 ` [PATCH v20 8/9] mm: memory_hotplug: disable memmap_on_memory when hugetlb_free_vmemmap enabled Muchun Song
@ 2021-04-15  8:40 ` Muchun Song
  8 siblings, 0 replies; 24+ messages in thread
From: Muchun Song @ 2021-04-15  8:40 UTC (permalink / raw)
  To: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, pawan.kumar.gupta, rdunlap,
	oneukum, anshuman.khandual, jroedel, almasrymina, rientjes,
	willy, osalvador, mhocko, song.bao.hua, david, naoya.horiguchi,
	joao.m.martins
  Cc: duanxiongchun, fam.zheng, linux-doc, linux-kernel, linux-mm,
	linux-fsdevel, Muchun Song, Miaohe Lin, Chen Huang,
	Bodeddula Balasubramaniam

All the infrastructure is ready, so we introduce nr_free_vmemmap_pages
field in the hstate to indicate how many vmemmap pages associated with
a HugeTLB page that can be freed to buddy allocator. And initialize it
in the hugetlb_vmemmap_init(). This patch is actual enablement of the
feature.

There are only (RESERVE_VMEMMAP_SIZE / sizeof(struct page)) struct
page structs that can be used when CONFIG_HUGETLB_PAGE_FREE_VMEMMAP,
so add a BUILD_BUG_ON to catch invalid usage of the tail struct page.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Tested-by: Chen Huang <chenhuang5@huawei.com>
Tested-by: Bodeddula Balasubramaniam <bodeddub@amazon.com>
---
 include/linux/hugetlb.h |  3 +++
 mm/hugetlb.c            |  1 +
 mm/hugetlb_vmemmap.c    | 33 +++++++++++++++++++++++++++++++++
 mm/hugetlb_vmemmap.h    | 10 ++++++----
 4 files changed, 43 insertions(+), 4 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 4015cedacf91..710d821fbca6 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -602,6 +602,9 @@ struct hstate {
 	unsigned int nr_huge_pages_node[MAX_NUMNODES];
 	unsigned int free_huge_pages_node[MAX_NUMNODES];
 	unsigned int surplus_huge_pages_node[MAX_NUMNODES];
+#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+	unsigned int nr_free_vmemmap_pages;
+#endif
 #ifdef CONFIG_CGROUP_HUGETLB
 	/* cgroup control files */
 	struct cftype cgroup_files_dfl[7];
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 1c37f0098e00..8adf52f4c7e4 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3361,6 +3361,7 @@ void __init hugetlb_add_hstate(unsigned int order)
 	h->next_nid_to_free = first_memory_node;
 	snprintf(h->name, HSTATE_NAME_LEN, "hugepages-%lukB",
 					huge_page_size(h)/1024);
+	hugetlb_vmemmap_init(h);
 
 	parsed_hstate = h;
 }
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 3070e1465b1b..f9f9bb212319 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -262,3 +262,36 @@ void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 
 	SetHPageVmemmapOptimized(head);
 }
+
+void __init hugetlb_vmemmap_init(struct hstate *h)
+{
+	unsigned int nr_pages = pages_per_huge_page(h);
+	unsigned int vmemmap_pages;
+
+	/*
+	 * There are only (RESERVE_VMEMMAP_SIZE / sizeof(struct page)) struct
+	 * page structs that can be used when CONFIG_HUGETLB_PAGE_FREE_VMEMMAP,
+	 * so add a BUILD_BUG_ON to catch invalid usage of the tail struct page.
+	 */
+	BUILD_BUG_ON(__NR_USED_SUBPAGE >=
+		     RESERVE_VMEMMAP_SIZE / sizeof(struct page));
+
+	if (!hugetlb_free_vmemmap_enabled)
+		return;
+
+	vmemmap_pages = (nr_pages * sizeof(struct page)) >> PAGE_SHIFT;
+	/*
+	 * The head page and the first tail page are not to be freed to buddy
+	 * allocator, the other pages will map to the first tail page, so they
+	 * can be freed.
+	 *
+	 * Could RESERVE_VMEMMAP_NR be greater than @vmemmap_pages? It is true
+	 * on some architectures (e.g. aarch64). See Documentation/arm64/
+	 * hugetlbpage.rst for more details.
+	 */
+	if (likely(vmemmap_pages > RESERVE_VMEMMAP_NR))
+		h->nr_free_vmemmap_pages = vmemmap_pages - RESERVE_VMEMMAP_NR;
+
+	pr_info("can free %d vmemmap pages for %s\n", h->nr_free_vmemmap_pages,
+		h->name);
+}
diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
index a37771b0b82a..cb2bef8f9e73 100644
--- a/mm/hugetlb_vmemmap.h
+++ b/mm/hugetlb_vmemmap.h
@@ -13,17 +13,15 @@
 #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
 int alloc_huge_page_vmemmap(struct hstate *h, struct page *head);
 void free_huge_page_vmemmap(struct hstate *h, struct page *head);
+void hugetlb_vmemmap_init(struct hstate *h);
 
 /*
  * How many vmemmap pages associated with a HugeTLB page that can be freed
  * to the buddy allocator.
- *
- * Todo: Returns zero for now, which means the feature is disabled. We will
- * enable it once all the infrastructure is there.
  */
 static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
 {
-	return 0;
+	return h->nr_free_vmemmap_pages;
 }
 #else
 static inline int alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
@@ -35,6 +33,10 @@ static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 {
 }
 
+static inline void hugetlb_vmemmap_init(struct hstate *h)
+{
+}
+
 static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
 {
 	return 0;
-- 
2.11.0


^ permalink raw reply	[flat|nested] 24+ messages in thread

* Re: [PATCH v20 3/9] mm: hugetlb: gather discrete indexes of tail page
  2021-04-15  8:39 ` [PATCH v20 3/9] mm: hugetlb: gather discrete indexes of tail page Muchun Song
@ 2021-04-16 18:54   ` Mike Kravetz
  0 siblings, 0 replies; 24+ messages in thread
From: Mike Kravetz @ 2021-04-16 18:54 UTC (permalink / raw)
  To: Muchun Song, corbet, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, pawan.kumar.gupta, rdunlap,
	oneukum, anshuman.khandual, jroedel, almasrymina, rientjes,
	willy, osalvador, mhocko, song.bao.hua, david, naoya.horiguchi,
	joao.m.martins
  Cc: duanxiongchun, fam.zheng, linux-doc, linux-kernel, linux-mm,
	linux-fsdevel, Miaohe Lin, Chen Huang, Bodeddula Balasubramaniam

On 4/15/21 1:39 AM, Muchun Song wrote:
> For HugeTLB page, there are more metadata to save in the struct page.
> But the head struct page cannot meet our needs, so we have to abuse
> other tail struct page to store the metadata. In order to avoid
> conflicts caused by subsequent use of more tail struct pages, we can
> gather these discrete indexes of tail struct page. In this case, it
> will be easier to add a new tail page index later.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
> Tested-by: Chen Huang <chenhuang5@huawei.com>
> Tested-by: Bodeddula Balasubramaniam <bodeddub@amazon.com>
> Acked-by: Michal Hocko <mhocko@suse.com>

Thanks,

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>

-- 
Mike Kravetz

^ permalink raw reply	[flat|nested] 24+ messages in thread

* Re: [PATCH v20 4/9] mm: hugetlb: free the vmemmap pages associated with each HugeTLB page
  2021-04-15  8:40 ` [PATCH v20 4/9] mm: hugetlb: free the vmemmap pages associated with each HugeTLB page Muchun Song
@ 2021-04-16 21:10   ` Mike Kravetz
  2021-04-17  2:55     ` [External] " Muchun Song
  0 siblings, 1 reply; 24+ messages in thread
From: Mike Kravetz @ 2021-04-16 21:10 UTC (permalink / raw)
  To: Muchun Song, corbet, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, pawan.kumar.gupta, rdunlap,
	oneukum, anshuman.khandual, jroedel, almasrymina, rientjes,
	willy, osalvador, mhocko, song.bao.hua, david, naoya.horiguchi,
	joao.m.martins
  Cc: duanxiongchun, fam.zheng, linux-doc, linux-kernel, linux-mm,
	linux-fsdevel, Chen Huang, Bodeddula Balasubramaniam

On 4/15/21 1:40 AM, Muchun Song wrote:
> Every HugeTLB has more than one struct page structure. We __know__ that
> we only use the first 4 (__NR_USED_SUBPAGE) struct page structures
> to store metadata associated with each HugeTLB.
> 
> There are a lot of struct page structures associated with each HugeTLB
> page. For tail pages, the value of compound_head is the same. So we can
> reuse first page of tail page structures. We map the virtual addresses
> of the remaining pages of tail page structures to the first tail page
> struct, and then free these page frames. Therefore, we need to reserve
> two pages as vmemmap areas.
> 
> When we allocate a HugeTLB page from the buddy, we can free some vmemmap
> pages associated with each HugeTLB page. It is more appropriate to do it
> in the prep_new_huge_page().
> 
> The free_vmemmap_pages_per_hpage(), which indicates how many vmemmap
> pages associated with a HugeTLB page can be freed, returns zero for
> now, which means the feature is disabled. We will enable it once all
> the infrastructure is there.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Tested-by: Chen Huang <chenhuang5@huawei.com>
> Tested-by: Bodeddula Balasubramaniam <bodeddub@amazon.com>
> Acked-by: Michal Hocko <mhocko@suse.com>

There may need to be some trivial rebasing due to Oscar's changes
when they go in.

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
-- 
Mike Kravetz

^ permalink raw reply	[flat|nested] 24+ messages in thread

* Re: [PATCH v20 5/9] mm: hugetlb: defer freeing of HugeTLB pages
  2021-04-15  8:40 ` [PATCH v20 5/9] mm: hugetlb: defer freeing of HugeTLB pages Muchun Song
@ 2021-04-16 23:55   ` Mike Kravetz
  2021-04-17  4:13     ` [External] " Muchun Song
  0 siblings, 1 reply; 24+ messages in thread
From: Mike Kravetz @ 2021-04-16 23:55 UTC (permalink / raw)
  To: Muchun Song, corbet, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, pawan.kumar.gupta, rdunlap,
	oneukum, anshuman.khandual, jroedel, almasrymina, rientjes,
	willy, osalvador, mhocko, song.bao.hua, david, naoya.horiguchi,
	joao.m.martins
  Cc: duanxiongchun, fam.zheng, linux-doc, linux-kernel, linux-mm,
	linux-fsdevel

On 4/15/21 1:40 AM, Muchun Song wrote:
> In the subsequent patch, we should allocate the vmemmap pages when
> freeing a HugeTLB page. But update_and_free_page() can be called
> under any context, so we cannot use GFP_KERNEL to allocate vmemmap
> pages. However, we can defer the actual freeing in a kworker to
> prevent from using GFP_ATOMIC to allocate the vmemmap pages.

Thanks!  I knew we would need to introduce a kworker for this when I
removed the kworker previously used in free_huge_page.

> The __update_and_free_page() is where the call to allocate vmemmmap
> pages will be inserted.

This patch adds the functionality required for __update_and_free_page
to potentially sleep and fail.  More questions will come up in the
subsequent patch when code must deal with the failures.

> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  mm/hugetlb.c         | 73 ++++++++++++++++++++++++++++++++++++++++++++++++----
>  mm/hugetlb_vmemmap.c | 12 ---------
>  mm/hugetlb_vmemmap.h | 17 ++++++++++++
>  3 files changed, 85 insertions(+), 17 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 923d05e2806b..eeb8f5480170 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1376,7 +1376,7 @@ static void remove_hugetlb_page(struct hstate *h, struct page *page,
>  	h->nr_huge_pages_node[nid]--;
>  }
>  
> -static void update_and_free_page(struct hstate *h, struct page *page)
> +static void __update_and_free_page(struct hstate *h, struct page *page)
>  {
>  	int i;
>  	struct page *subpage = page;
> @@ -1399,12 +1399,73 @@ static void update_and_free_page(struct hstate *h, struct page *page)
>  	}
>  }
>  
> +/*
> + * As update_and_free_page() can be called under any context, so we cannot
> + * use GFP_KERNEL to allocate vmemmap pages. However, we can defer the
> + * actual freeing in a workqueue to prevent from using GFP_ATOMIC to allocate
> + * the vmemmap pages.
> + *
> + * free_hpage_workfn() locklessly retrieves the linked list of pages to be
> + * freed and frees them one-by-one. As the page->mapping pointer is going
> + * to be cleared in free_hpage_workfn() anyway, it is reused as the llist_node
> + * structure of a lockless linked list of huge pages to be freed.
> + */
> +static LLIST_HEAD(hpage_freelist);
> +
> +static void free_hpage_workfn(struct work_struct *work)
> +{
> +	struct llist_node *node;
> +
> +	node = llist_del_all(&hpage_freelist);
> +
> +	while (node) {
> +		struct page *page;
> +		struct hstate *h;
> +
> +		page = container_of((struct address_space **)node,
> +				     struct page, mapping);
> +		node = node->next;
> +		page->mapping = NULL;
> +		h = page_hstate(page);

The VM_BUG_ON_PAGE(!PageHuge(page), page) in page_hstate is going to
trigger because a previous call to remove_hugetlb_page() will
set_compound_page_dtor(page, NULL_COMPOUND_DTOR)

Note how h(hstate) is grabbed before calling update_and_free_page in
existing code.

We could potentially drop the !PageHuge(page) in page_hstate.  Or,
perhaps just use 'size_to_hstate(page_size(page))' in free_hpage_workfn.
-- 
Mike Kravetz

> +
> +		__update_and_free_page(h, page);
> +
> +		cond_resched();
> +	}
> +}
> +static DECLARE_WORK(free_hpage_work, free_hpage_workfn);
> +
> +static inline void flush_free_hpage_work(struct hstate *h)
> +{
> +	if (free_vmemmap_pages_per_hpage(h))
> +		flush_work(&free_hpage_work);
> +}
> +
> +static void update_and_free_page(struct hstate *h, struct page *page,
> +				 bool atomic)
> +{
> +	if (!free_vmemmap_pages_per_hpage(h) || !atomic) {
> +		__update_and_free_page(h, page);
> +		return;
> +	}
> +
> +	/*
> +	 * Defer freeing to avoid using GFP_ATOMIC to allocate vmemmap pages.
> +	 *
> +	 * Only call schedule_work() if hpage_freelist is previously
> +	 * empty. Otherwise, schedule_work() had been called but the workfn
> +	 * hasn't retrieved the list yet.
> +	 */
> +	if (llist_add((struct llist_node *)&page->mapping, &hpage_freelist))
> +		schedule_work(&free_hpage_work);
> +}
> +
>  static void update_and_free_pages_bulk(struct hstate *h, struct list_head *list)
>  {
>  	struct page *page, *t_page;
>  
>  	list_for_each_entry_safe(page, t_page, list, lru) {
> -		update_and_free_page(h, page);
> +		update_and_free_page(h, page, false);
>  		cond_resched();
>  	}
>  }
> @@ -1471,12 +1532,12 @@ void free_huge_page(struct page *page)
>  	if (HPageTemporary(page)) {
>  		remove_hugetlb_page(h, page, false);
>  		spin_unlock_irqrestore(&hugetlb_lock, flags);
> -		update_and_free_page(h, page);
> +		update_and_free_page(h, page, true);
>  	} else if (h->surplus_huge_pages_node[nid]) {
>  		/* remove the page from active list */
>  		remove_hugetlb_page(h, page, true);
>  		spin_unlock_irqrestore(&hugetlb_lock, flags);
> -		update_and_free_page(h, page);
> +		update_and_free_page(h, page, true);
>  	} else {
>  		arch_clear_hugepage_flags(page);
>  		enqueue_huge_page(h, page);
> @@ -1785,7 +1846,7 @@ int dissolve_free_huge_page(struct page *page)
>  		remove_hugetlb_page(h, page, false);
>  		h->max_huge_pages--;
>  		spin_unlock_irq(&hugetlb_lock);
> -		update_and_free_page(h, head);
> +		update_and_free_page(h, head, false);
>  		return 0;
>  	}
>  out:
> @@ -2627,6 +2688,7 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
>  	 * pages in hstate via the proc/sysfs interfaces.
>  	 */
>  	mutex_lock(&h->resize_lock);
> +	flush_free_hpage_work(h);
>  	spin_lock_irq(&hugetlb_lock);
>  
>  	/*
> @@ -2736,6 +2798,7 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
>  	/* free the pages after dropping lock */
>  	spin_unlock_irq(&hugetlb_lock);
>  	update_and_free_pages_bulk(h, &page_list);
> +	flush_free_hpage_work(h);
>  	spin_lock_irq(&hugetlb_lock);
>  
>  	while (count < persistent_huge_pages(h)) {
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index e45a138a7f85..cb28c5b6c9ff 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -180,18 +180,6 @@
>  #define RESERVE_VMEMMAP_NR		2U
>  #define RESERVE_VMEMMAP_SIZE		(RESERVE_VMEMMAP_NR << PAGE_SHIFT)
>  
> -/*
> - * How many vmemmap pages associated with a HugeTLB page that can be freed
> - * to the buddy allocator.
> - *
> - * Todo: Returns zero for now, which means the feature is disabled. We will
> - * enable it once all the infrastructure is there.
> - */
> -static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
> -{
> -	return 0;
> -}
> -
>  static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
>  {
>  	return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
> diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
> index 6923f03534d5..01f8637adbe0 100644
> --- a/mm/hugetlb_vmemmap.h
> +++ b/mm/hugetlb_vmemmap.h
> @@ -12,9 +12,26 @@
>  
>  #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
>  void free_huge_page_vmemmap(struct hstate *h, struct page *head);
> +
> +/*
> + * How many vmemmap pages associated with a HugeTLB page that can be freed
> + * to the buddy allocator.
> + *
> + * Todo: Returns zero for now, which means the feature is disabled. We will
> + * enable it once all the infrastructure is there.
> + */
> +static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
> +{
> +	return 0;
> +}
>  #else
>  static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head)
>  {
>  }
> +
> +static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
> +{
> +	return 0;
> +}
>  #endif /* CONFIG_HUGETLB_PAGE_FREE_VMEMMAP */
>  #endif /* _LINUX_HUGETLB_VMEMMAP_H */
> 

^ permalink raw reply	[flat|nested] 24+ messages in thread

* Re: [External] Re: [PATCH v20 4/9] mm: hugetlb: free the vmemmap pages associated with each HugeTLB page
  2021-04-16 21:10   ` Mike Kravetz
@ 2021-04-17  2:55     ` Muchun Song
  0 siblings, 0 replies; 24+ messages in thread
From: Muchun Song @ 2021-04-17  2:55 UTC (permalink / raw)
  To: Mike Kravetz
  Cc: Jonathan Corbet, Thomas Gleixner, Ingo Molnar, bp, X86 ML, hpa,
	dave.hansen, luto, Peter Zijlstra, Alexander Viro, Andrew Morton,
	paulmck, pawan.kumar.gupta, Randy Dunlap, oneukum,
	anshuman.khandual, jroedel, Mina Almasry, David Rientjes,
	Matthew Wilcox, Oscar Salvador, Michal Hocko,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, fam.zheng, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel, Chen Huang,
	Bodeddula Balasubramaniam

On Sat, Apr 17, 2021 at 5:10 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 4/15/21 1:40 AM, Muchun Song wrote:
> > Every HugeTLB has more than one struct page structure. We __know__ that
> > we only use the first 4 (__NR_USED_SUBPAGE) struct page structures
> > to store metadata associated with each HugeTLB.
> >
> > There are a lot of struct page structures associated with each HugeTLB
> > page. For tail pages, the value of compound_head is the same. So we can
> > reuse first page of tail page structures. We map the virtual addresses
> > of the remaining pages of tail page structures to the first tail page
> > struct, and then free these page frames. Therefore, we need to reserve
> > two pages as vmemmap areas.
> >
> > When we allocate a HugeTLB page from the buddy, we can free some vmemmap
> > pages associated with each HugeTLB page. It is more appropriate to do it
> > in the prep_new_huge_page().
> >
> > The free_vmemmap_pages_per_hpage(), which indicates how many vmemmap
> > pages associated with a HugeTLB page can be freed, returns zero for
> > now, which means the feature is disabled. We will enable it once all
> > the infrastructure is there.
> >
> > Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> > Reviewed-by: Oscar Salvador <osalvador@suse.de>
> > Tested-by: Chen Huang <chenhuang5@huawei.com>
> > Tested-by: Bodeddula Balasubramaniam <bodeddub@amazon.com>
> > Acked-by: Michal Hocko <mhocko@suse.com>
>
> There may need to be some trivial rebasing due to Oscar's changes
> when they go in.

Yeah, thanks for your reminder.

>
> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
> --
> Mike Kravetz

^ permalink raw reply	[flat|nested] 24+ messages in thread

* Re: [External] Re: [PATCH v20 5/9] mm: hugetlb: defer freeing of HugeTLB pages
  2021-04-16 23:55   ` Mike Kravetz
@ 2021-04-17  4:13     ` Muchun Song
  0 siblings, 0 replies; 24+ messages in thread
From: Muchun Song @ 2021-04-17  4:13 UTC (permalink / raw)
  To: Mike Kravetz
  Cc: Jonathan Corbet, Thomas Gleixner, Ingo Molnar, bp, X86 ML, hpa,
	dave.hansen, luto, Peter Zijlstra, Alexander Viro, Andrew Morton,
	paulmck, pawan.kumar.gupta, Randy Dunlap, oneukum,
	anshuman.khandual, jroedel, Mina Almasry, David Rientjes,
	Matthew Wilcox, Oscar Salvador, Michal Hocko,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, fam.zheng, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Sat, Apr 17, 2021 at 7:56 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 4/15/21 1:40 AM, Muchun Song wrote:
> > In the subsequent patch, we should allocate the vmemmap pages when
> > freeing a HugeTLB page. But update_and_free_page() can be called
> > under any context, so we cannot use GFP_KERNEL to allocate vmemmap
> > pages. However, we can defer the actual freeing in a kworker to
> > prevent from using GFP_ATOMIC to allocate the vmemmap pages.
>
> Thanks!  I knew we would need to introduce a kworker for this when I
> removed the kworker previously used in free_huge_page.

Yeah, but another choice is using GFP_ATOMIC to allocate vmemmap
pages when we are in an atomic context. If not atomic context, just
use GFP_KERNEL. In this case, we can drop kworker.

>
> > The __update_and_free_page() is where the call to allocate vmemmmap
> > pages will be inserted.
>
> This patch adds the functionality required for __update_and_free_page
> to potentially sleep and fail.  More questions will come up in the
> subsequent patch when code must deal with the failures.

Right. More questions are welcome.

>
> >
> > Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> > ---
> >  mm/hugetlb.c         | 73 ++++++++++++++++++++++++++++++++++++++++++++++++----
> >  mm/hugetlb_vmemmap.c | 12 ---------
> >  mm/hugetlb_vmemmap.h | 17 ++++++++++++
> >  3 files changed, 85 insertions(+), 17 deletions(-)
> >
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index 923d05e2806b..eeb8f5480170 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -1376,7 +1376,7 @@ static void remove_hugetlb_page(struct hstate *h, struct page *page,
> >       h->nr_huge_pages_node[nid]--;
> >  }
> >
> > -static void update_and_free_page(struct hstate *h, struct page *page)
> > +static void __update_and_free_page(struct hstate *h, struct page *page)
> >  {
> >       int i;
> >       struct page *subpage = page;
> > @@ -1399,12 +1399,73 @@ static void update_and_free_page(struct hstate *h, struct page *page)
> >       }
> >  }
> >
> > +/*
> > + * As update_and_free_page() can be called under any context, so we cannot
> > + * use GFP_KERNEL to allocate vmemmap pages. However, we can defer the
> > + * actual freeing in a workqueue to prevent from using GFP_ATOMIC to allocate
> > + * the vmemmap pages.
> > + *
> > + * free_hpage_workfn() locklessly retrieves the linked list of pages to be
> > + * freed and frees them one-by-one. As the page->mapping pointer is going
> > + * to be cleared in free_hpage_workfn() anyway, it is reused as the llist_node
> > + * structure of a lockless linked list of huge pages to be freed.
> > + */
> > +static LLIST_HEAD(hpage_freelist);
> > +
> > +static void free_hpage_workfn(struct work_struct *work)
> > +{
> > +     struct llist_node *node;
> > +
> > +     node = llist_del_all(&hpage_freelist);
> > +
> > +     while (node) {
> > +             struct page *page;
> > +             struct hstate *h;
> > +
> > +             page = container_of((struct address_space **)node,
> > +                                  struct page, mapping);
> > +             node = node->next;
> > +             page->mapping = NULL;
> > +             h = page_hstate(page);
>
> The VM_BUG_ON_PAGE(!PageHuge(page), page) in page_hstate is going to
> trigger because a previous call to remove_hugetlb_page() will
> set_compound_page_dtor(page, NULL_COMPOUND_DTOR)

Sorry, I did not realise that. Thanks for your reminder.

>
> Note how h(hstate) is grabbed before calling update_and_free_page in
> existing code.
>
> We could potentially drop the !PageHuge(page) in page_hstate.  Or,
> perhaps just use 'size_to_hstate(page_size(page))' in free_hpage_workfn.

I prefer not to change the behavior of page_hstate(). So I
should use 'size_to_hstate(page_size(page))' directly.

Thanks Mike.


> --
> Mike Kravetz

^ permalink raw reply	[flat|nested] 24+ messages in thread

* Re: [PATCH v20 6/9] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-04-15  8:40 ` [PATCH v20 6/9] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page Muchun Song
@ 2021-04-19 23:19   ` Mike Kravetz
  2021-04-20  8:46     ` [External] " Muchun Song
  0 siblings, 1 reply; 24+ messages in thread
From: Mike Kravetz @ 2021-04-19 23:19 UTC (permalink / raw)
  To: Muchun Song, corbet, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, pawan.kumar.gupta, rdunlap,
	oneukum, anshuman.khandual, jroedel, almasrymina, rientjes,
	willy, osalvador, mhocko, song.bao.hua, david, naoya.horiguchi,
	joao.m.martins
  Cc: duanxiongchun, fam.zheng, linux-doc, linux-kernel, linux-mm,
	linux-fsdevel

On 4/15/21 1:40 AM, Muchun Song wrote:
> When we free a HugeTLB page to the buddy allocator, we need to allocate
> the vmemmap pages associated with it. However, we may not be able to
> allocate the vmemmap pages when the system is under memory pressure. In
> this case, we just refuse to free the HugeTLB page. This changes behavior
> in some corner cases as listed below:
> 
>  1) Failing to free a huge page triggered by the user (decrease nr_pages).
> 
>     User needs to try again later.
> 
>  2) Failing to free a surplus huge page when freed by the application.
> 
>     Try again later when freeing a huge page next time.
> 
>  3) Failing to dissolve a free huge page on ZONE_MOVABLE via
>     offline_pages().
> 
>     This can happen when we have plenty of ZONE_MOVABLE memory, but
>     not enough kernel memory to allocate vmemmmap pages.  We may even
>     be able to migrate huge page contents, but will not be able to
>     dissolve the source huge page.  This will prevent an offline
>     operation and is unfortunate as memory offlining is expected to
>     succeed on movable zones.  Users that depend on memory hotplug
>     to succeed for movable zones should carefully consider whether the
>     memory savings gained from this feature are worth the risk of
>     possibly not being able to offline memory in certain situations.
> 
>  4) Failing to dissolve a huge page on CMA/ZONE_MOVABLE via
>     alloc_contig_range() - once we have that handling in place. Mainly
>     affects CMA and virtio-mem.
> 
>     Similar to 3). virito-mem will handle migration errors gracefully.
>     CMA might be able to fallback on other free areas within the CMA
>     region.
> 
> Vmemmap pages are allocated from the page freeing context. In order for
> those allocations to be not disruptive (e.g. trigger oom killer)
> __GFP_NORETRY is used. hugetlb_lock is dropped for the allocation
> because a non sleeping allocation would be too fragile and it could fail
> too easily under memory pressure. GFP_ATOMIC or other modes to access
> memory reserves is not used because we want to prevent consuming
> reserves under heavy hugetlb freeing.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  Documentation/admin-guide/mm/hugetlbpage.rst    |  8 +++
>  Documentation/admin-guide/mm/memory-hotplug.rst | 13 ++++
>  include/linux/hugetlb.h                         |  3 +
>  include/linux/mm.h                              |  2 +
>  mm/hugetlb.c                                    | 85 ++++++++++++++++++++-----
>  mm/hugetlb_vmemmap.c                            | 34 ++++++++++
>  mm/hugetlb_vmemmap.h                            |  6 ++
>  mm/sparse-vmemmap.c                             | 75 +++++++++++++++++++++-
>  8 files changed, 210 insertions(+), 16 deletions(-)
> 
> diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst
> index f7b1c7462991..6988895d09a8 100644
> --- a/Documentation/admin-guide/mm/hugetlbpage.rst
> +++ b/Documentation/admin-guide/mm/hugetlbpage.rst
> @@ -60,6 +60,10 @@ HugePages_Surp
>          the pool above the value in ``/proc/sys/vm/nr_hugepages``. The
>          maximum number of surplus huge pages is controlled by
>          ``/proc/sys/vm/nr_overcommit_hugepages``.
> +	Note: When the feature of freeing unused vmemmap pages associated
> +	with each hugetlb page is enabled, the number of surplus huge pages
> +	may be temporarily larger than the maximum number of surplus huge
> +	pages when the system is under memory pressure.
>  Hugepagesize
>  	is the default hugepage size (in Kb).
>  Hugetlb
> @@ -80,6 +84,10 @@ returned to the huge page pool when freed by a task.  A user with root
>  privileges can dynamically allocate more or free some persistent huge pages
>  by increasing or decreasing the value of ``nr_hugepages``.
>  
> +Note: When the feature of freeing unused vmemmap pages associated with each
> +hugetlb page is enabled, we can fail to free the huge pages triggered by
> +the user when ths system is under memory pressure.  Please try again later.
> +
>  Pages that are used as huge pages are reserved inside the kernel and cannot
>  be used for other purposes.  Huge pages cannot be swapped out under
>  memory pressure.
> diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
> index 05d51d2d8beb..c6bae2d77160 100644
> --- a/Documentation/admin-guide/mm/memory-hotplug.rst
> +++ b/Documentation/admin-guide/mm/memory-hotplug.rst
> @@ -357,6 +357,19 @@ creates ZONE_MOVABLE as following.
>     Unfortunately, there is no information to show which memory block belongs
>     to ZONE_MOVABLE. This is TBD.
>  
> +   Memory offlining can fail when dissolving a free huge page on ZONE_MOVABLE
> +   and the feature of freeing unused vmemmap pages associated with each hugetlb
> +   page is enabled.
> +
> +   This can happen when we have plenty of ZONE_MOVABLE memory, but not enough
> +   kernel memory to allocate vmemmmap pages.  We may even be able to migrate
> +   huge page contents, but will not be able to dissolve the source huge page.
> +   This will prevent an offline operation and is unfortunate as memory offlining
> +   is expected to succeed on movable zones.  Users that depend on memory hotplug
> +   to succeed for movable zones should carefully consider whether the memory
> +   savings gained from this feature are worth the risk of possibly not being
> +   able to offline memory in certain situations.
> +
>  .. note::
>     Techniques that rely on long-term pinnings of memory (especially, RDMA and
>     vfio) are fundamentally problematic with ZONE_MOVABLE and, therefore, memory
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 0abed7e766b8..6e970a7d3480 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -525,6 +525,7 @@ unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
>   *	code knows it has only reference.  All other examinations and
>   *	modifications require hugetlb_lock.
>   * HPG_freed - Set when page is on the free lists.
> + * HPG_vmemmap_optimized - Set when the vmemmap pages of the page are freed.
>   *	Synchronization: hugetlb_lock held for examination and modification.

I like the per-page flag.  In previous versions of the series, you just
checked the free_vmemmap_pages_per_hpage() to determine if vmemmmap
should be allocated.  Is there any change in functionality that makes is
necessary to set the flag in each page, or is it mostly for flexability
going forward?

>   */
>  enum hugetlb_page_flags {
> @@ -532,6 +533,7 @@ enum hugetlb_page_flags {
>  	HPG_migratable,
>  	HPG_temporary,
>  	HPG_freed,
> +	HPG_vmemmap_optimized,
>  	__NR_HPAGEFLAGS,
>  };
>  
> @@ -577,6 +579,7 @@ HPAGEFLAG(RestoreReserve, restore_reserve)
>  HPAGEFLAG(Migratable, migratable)
>  HPAGEFLAG(Temporary, temporary)
>  HPAGEFLAG(Freed, freed)
> +HPAGEFLAG(VmemmapOptimized, vmemmap_optimized)
>  
>  #ifdef CONFIG_HUGETLB_PAGE
>  
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index a4d160ddb749..d0854828bb9c 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3048,6 +3048,8 @@ static inline void print_vma_addr(char *prefix, unsigned long rip)
>  
>  void vmemmap_remap_free(unsigned long start, unsigned long end,
>  			unsigned long reuse);
> +int vmemmap_remap_alloc(unsigned long start, unsigned long end,
> +			unsigned long reuse, gfp_t gfp_mask);
>  
>  void *sparse_buffer_alloc(unsigned long size);
>  struct page * __populate_section_memmap(unsigned long pfn,
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index eeb8f5480170..1c37f0098e00 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1376,6 +1376,34 @@ static void remove_hugetlb_page(struct hstate *h, struct page *page,
>  	h->nr_huge_pages_node[nid]--;
>  }
>  
> +static void add_hugetlb_page(struct hstate *h, struct page *page,
> +			     bool adjust_surplus)
> +{

We need to be a bit careful with hugepage specific flags that may be
set.  The routine remove_hugetlb_page which is called for 'page' before
this routine will not clear any of the hugepage specific flags.  If the
calling path goes through free_huge_page, most but not all flags are
cleared.

We had a discussion about clearing the page->private field in Oscar's
series.  In the case of 'new' pages we can assume page->private is
cleared, but perhaps we should not make that assumption here.  Since we
hope to rarely call this routine, it might be safer to do something
like:

	set_page_private(page, 0);
	SetHPageVmemmapOptimized(page);

> +	int nid = page_to_nid(page);
> +
> +	lockdep_assert_held(&hugetlb_lock);
> +
> +	INIT_LIST_HEAD(&page->lru);
> +	h->nr_huge_pages++;
> +	h->nr_huge_pages_node[nid]++;
> +
> +	if (adjust_surplus) {
> +		h->surplus_huge_pages++;
> +		h->surplus_huge_pages_node[nid]++;
> +	}
> +
> +	set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
> +
> +	/*
> +	 * The refcount can possibly be increased by memory-failure or
> +	 * soft_offline handlers.
> +	 */
> +	if (likely(put_page_testzero(page))) {

In the existing code there is no such test.  Is the need for the test
because of something introduced in the new code?  Or, should this test
be in the existing code?

Sorry, I am not seeing why this is needed.

> +		arch_clear_hugepage_flags(page);
> +		enqueue_huge_page(h, page);
> +	}
> +}
> +
>  static void __update_and_free_page(struct hstate *h, struct page *page)
>  {
>  	int i;
> @@ -1384,6 +1412,18 @@ static void __update_and_free_page(struct hstate *h, struct page *page)
>  	if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
>  		return;
>  
> +	if (alloc_huge_page_vmemmap(h, page)) {
> +		spin_lock_irq(&hugetlb_lock);
> +		/*
> +		 * If we cannot allocate vmemmap pages, just refuse to free the
> +		 * page and put the page back on the hugetlb free list and treat
> +		 * as a surplus page.
> +		 */
> +		add_hugetlb_page(h, page, true);
> +		spin_unlock_irq(&hugetlb_lock);
> +		return;
> +	}
> +
>  	for (i = 0; i < pages_per_huge_page(h);
>  	     i++, subpage = mem_map_next(subpage, page, i)) {
>  		subpage->flags &= ~(1 << PG_locked | 1 << PG_error |
> @@ -1444,7 +1484,7 @@ static inline void flush_free_hpage_work(struct hstate *h)
>  static void update_and_free_page(struct hstate *h, struct page *page,
>  				 bool atomic)
>  {
> -	if (!free_vmemmap_pages_per_hpage(h) || !atomic) {
> +	if (!HPageVmemmapOptimized(page) || !atomic) {
>  		__update_and_free_page(h, page);
>  		return;
>  	}

When update_and_free_pages_bulk was added it was done to avoid
lock/unlock cycles with each page.  At the time, I thought about the
addition of code to allocate vmmemmap, and the possibility that those
allocations could fail.  I thought it might make sense to perhaps
process the pages one at a time so that we could quit at the first
allocation failure.  After more thought, I think it is best to leave the
code to do bulk operations as you have done above.  Why?
- Just because one allocation fails does not mean the next will fail.
  It is possible the allocations could be from different nodes/zones.
- We will still need to put the requested number of pages into surplus
  state.

I am not suggesting you change anything.  Just wanted to share my
thoughts in case someone thought otherwise.

> @@ -1790,10 +1830,14 @@ static struct page *remove_pool_huge_page(struct hstate *h,
>   * nothing for in-use hugepages and non-hugepages.
>   * This function returns values like below:
>   *
> - *  -EBUSY: failed to dissolved free hugepages or the hugepage is in-use
> - *          (allocated or reserved.)
> - *       0: successfully dissolved free hugepages or the page is not a
> - *          hugepage (considered as already dissolved)
> + *  -ENOMEM: failed to allocate vmemmap pages to free the freed hugepages
> + *           when the system is under memory pressure and the feature of
> + *           freeing unused vmemmap pages associated with each hugetlb page
> + *           is enabled.
> + *  -EBUSY:  failed to dissolved free hugepages or the hugepage is in-use
> + *           (allocated or reserved.)
> + *       0:  successfully dissolved free hugepages or the page is not a
> + *           hugepage (considered as already dissolved)
>   */
>  int dissolve_free_huge_page(struct page *page)
>  {
> @@ -1835,19 +1879,30 @@ int dissolve_free_huge_page(struct page *page)
>  			goto retry;
>  		}
>  
> -		/*
> -		 * Move PageHWPoison flag from head page to the raw error page,
> -		 * which makes any subpages rather than the error page reusable.
> -		 */
> -		if (PageHWPoison(head) && page != head) {
> -			SetPageHWPoison(page);
> -			ClearPageHWPoison(head);
> -		}
>  		remove_hugetlb_page(h, page, false);
>  		h->max_huge_pages--;
>  		spin_unlock_irq(&hugetlb_lock);
> -		update_and_free_page(h, head, false);
> -		return 0;
> +
> +		rc = alloc_huge_page_vmemmap(h, page);
> +		if (!rc) {
> +			/*
> +			 * Move PageHWPoison flag from head page to the raw
> +			 * error page, which makes any subpages rather than
> +			 * the error page reusable.
> +			 */
> +			if (PageHWPoison(head) && page != head) {
> +				SetPageHWPoison(page);
> +				ClearPageHWPoison(head);
> +			}
> +			update_and_free_page(h, head, false);
> +		} else {
> +			spin_lock_irq(&hugetlb_lock);
> +			add_hugetlb_page(h, page, false);
> +			h->max_huge_pages++;
> +			spin_unlock_irq(&hugetlb_lock);
> +		}
> +
> +		return rc;
>  	}
>  out:
>  	spin_unlock_irq(&hugetlb_lock);

Changes in the files below have not changed in any significant way
since the previous version.  The code looks good to me, but I would
like to see if there are comments from others.

Thanks,
-- 
Mike Kravetz

> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index cb28c5b6c9ff..a897c7778246 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -185,6 +185,38 @@ static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
>  	return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
>  }
>  
> +/*
> + * Previously discarded vmemmap pages will be allocated and remapping
> + * after this function returns zero.
> + */
> +int alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
> +{
> +	int ret;
> +	unsigned long vmemmap_addr = (unsigned long)head;
> +	unsigned long vmemmap_end, vmemmap_reuse;
> +
> +	if (!HPageVmemmapOptimized(head))
> +		return 0;
> +
> +	vmemmap_addr += RESERVE_VMEMMAP_SIZE;
> +	vmemmap_end = vmemmap_addr + free_vmemmap_pages_size_per_hpage(h);
> +	vmemmap_reuse = vmemmap_addr - PAGE_SIZE;
> +	/*
> +	 * The pages which the vmemmap virtual address range [@vmemmap_addr,
> +	 * @vmemmap_end) are mapped to are freed to the buddy allocator, and
> +	 * the range is mapped to the page which @vmemmap_reuse is mapped to.
> +	 * When a HugeTLB page is freed to the buddy allocator, previously
> +	 * discarded vmemmap pages must be allocated and remapping.
> +	 */
> +	ret = vmemmap_remap_alloc(vmemmap_addr, vmemmap_end, vmemmap_reuse,
> +				  GFP_KERNEL | __GFP_NORETRY | __GFP_THISNODE);
> +
> +	if (!ret)
> +		ClearHPageVmemmapOptimized(head);
> +
> +	return ret;
> +}
> +
>  void free_huge_page_vmemmap(struct hstate *h, struct page *head)
>  {
>  	unsigned long vmemmap_addr = (unsigned long)head;
> @@ -203,4 +235,6 @@ void free_huge_page_vmemmap(struct hstate *h, struct page *head)
>  	 * which the range [@vmemmap_addr, @vmemmap_end] is mapped to.
>  	 */
>  	vmemmap_remap_free(vmemmap_addr, vmemmap_end, vmemmap_reuse);
> +
> +	SetHPageVmemmapOptimized(head);
>  }
> diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
> index 01f8637adbe0..a37771b0b82a 100644
> --- a/mm/hugetlb_vmemmap.h
> +++ b/mm/hugetlb_vmemmap.h
> @@ -11,6 +11,7 @@
>  #include <linux/hugetlb.h>
>  
>  #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
> +int alloc_huge_page_vmemmap(struct hstate *h, struct page *head);
>  void free_huge_page_vmemmap(struct hstate *h, struct page *head);
>  
>  /*
> @@ -25,6 +26,11 @@ static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
>  	return 0;
>  }
>  #else
> +static inline int alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
> +{
> +	return 0;
> +}
> +
>  static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head)
>  {
>  }
> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> index 7d40b5bd7046..693de0aec7a8 100644
> --- a/mm/sparse-vmemmap.c
> +++ b/mm/sparse-vmemmap.c
> @@ -40,7 +40,8 @@
>   * @remap_pte:		called for each lowest-level entry (PTE).
>   * @reuse_page:		the page which is reused for the tail vmemmap pages.
>   * @reuse_addr:		the virtual address of the @reuse_page page.
> - * @vmemmap_pages:	the list head of the vmemmap pages that can be freed.
> + * @vmemmap_pages:	the list head of the vmemmap pages that can be freed
> + *			or is mapped from.
>   */
>  struct vmemmap_remap_walk {
>  	void (*remap_pte)(pte_t *pte, unsigned long addr,
> @@ -224,6 +225,78 @@ void vmemmap_remap_free(unsigned long start, unsigned long end,
>  	free_vmemmap_page_list(&vmemmap_pages);
>  }
>  
> +static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
> +				struct vmemmap_remap_walk *walk)
> +{
> +	pgprot_t pgprot = PAGE_KERNEL;
> +	struct page *page;
> +	void *to;
> +
> +	BUG_ON(pte_page(*pte) != walk->reuse_page);
> +
> +	page = list_first_entry(walk->vmemmap_pages, struct page, lru);
> +	list_del(&page->lru);
> +	to = page_to_virt(page);
> +	copy_page(to, (void *)walk->reuse_addr);
> +
> +	set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot));
> +}
> +
> +static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
> +				   gfp_t gfp_mask, struct list_head *list)
> +{
> +	unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
> +	int nid = page_to_nid((struct page *)start);
> +	struct page *page, *next;
> +
> +	while (nr_pages--) {
> +		page = alloc_pages_node(nid, gfp_mask, 0);
> +		if (!page)
> +			goto out;
> +		list_add_tail(&page->lru, list);
> +	}
> +
> +	return 0;
> +out:
> +	list_for_each_entry_safe(page, next, list, lru)
> +		__free_pages(page, 0);
> +	return -ENOMEM;
> +}
> +
> +/**
> + * vmemmap_remap_alloc - remap the vmemmap virtual address range [@start, end)
> + *			 to the page which is from the @vmemmap_pages
> + *			 respectively.
> + * @start:	start address of the vmemmap virtual address range that we want
> + *		to remap.
> + * @end:	end address of the vmemmap virtual address range that we want to
> + *		remap.
> + * @reuse:	reuse address.
> + * @gpf_mask:	GFP flag for allocating vmemmap pages.
> + */
> +int vmemmap_remap_alloc(unsigned long start, unsigned long end,
> +			unsigned long reuse, gfp_t gfp_mask)
> +{
> +	LIST_HEAD(vmemmap_pages);
> +	struct vmemmap_remap_walk walk = {
> +		.remap_pte	= vmemmap_restore_pte,
> +		.reuse_addr	= reuse,
> +		.vmemmap_pages	= &vmemmap_pages,
> +	};
> +
> +	/* See the comment in the vmemmap_remap_free(). */
> +	BUG_ON(start - reuse != PAGE_SIZE);
> +
> +	might_sleep_if(gfpflags_allow_blocking(gfp_mask));
> +
> +	if (alloc_vmemmap_page_list(start, end, gfp_mask, &vmemmap_pages))
> +		return -ENOMEM;
> +
> +	vmemmap_remap_range(reuse, end, &walk);
> +
> +	return 0;
> +}
> +
>  /*
>   * Allocate a block of memory to be used to back the virtual memory map
>   * or to back the page tables that are used to create the mapping.
> 

^ permalink raw reply	[flat|nested] 24+ messages in thread

* Re: [PATCH v20 7/9] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap
  2021-04-15  8:40 ` [PATCH v20 7/9] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap Muchun Song
@ 2021-04-19 23:41   ` Mike Kravetz
  0 siblings, 0 replies; 24+ messages in thread
From: Mike Kravetz @ 2021-04-19 23:41 UTC (permalink / raw)
  To: Muchun Song, corbet, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, pawan.kumar.gupta, rdunlap,
	oneukum, anshuman.khandual, jroedel, almasrymina, rientjes,
	willy, osalvador, mhocko, song.bao.hua, david, naoya.horiguchi,
	joao.m.martins
  Cc: duanxiongchun, fam.zheng, linux-doc, linux-kernel, linux-mm,
	linux-fsdevel, Miaohe Lin, Chen Huang, Bodeddula Balasubramaniam

On 4/15/21 1:40 AM, Muchun Song wrote:
> Add a kernel parameter hugetlb_free_vmemmap to enable the feature of
> freeing unused vmemmap pages associated with each hugetlb page on boot.
> 
> We disables PMD mapping of vmemmap pages for x86-64 arch when this
> feature is enabled. Because vmemmap_remap_free() depends on vmemmap
> being base page mapped.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Reviewed-by: Barry Song <song.bao.hua@hisilicon.com>
> Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
> Tested-by: Chen Huang <chenhuang5@huawei.com>
> Tested-by: Bodeddula Balasubramaniam <bodeddub@amazon.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 17 +++++++++++++++++
>  Documentation/admin-guide/mm/hugetlbpage.rst    |  3 +++
>  arch/x86/mm/init_64.c                           |  8 ++++++--
>  include/linux/hugetlb.h                         | 19 +++++++++++++++++++
>  mm/hugetlb_vmemmap.c                            | 24 ++++++++++++++++++++++++
>  5 files changed, 69 insertions(+), 2 deletions(-)

Thanks,

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
-- 
Mike Kravetz

^ permalink raw reply	[flat|nested] 24+ messages in thread

* Re: [External] Re: [PATCH v20 6/9] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-04-19 23:19   ` Mike Kravetz
@ 2021-04-20  8:46     ` Muchun Song
  2021-04-20 17:48       ` Mike Kravetz
  0 siblings, 1 reply; 24+ messages in thread
From: Muchun Song @ 2021-04-20  8:46 UTC (permalink / raw)
  To: Mike Kravetz
  Cc: Jonathan Corbet, Thomas Gleixner, Ingo Molnar, bp, X86 ML, hpa,
	dave.hansen, luto, Peter Zijlstra, Alexander Viro, Andrew Morton,
	paulmck, pawan.kumar.gupta, Randy Dunlap, oneukum,
	anshuman.khandual, jroedel, Mina Almasry, David Rientjes,
	Matthew Wilcox, Oscar Salvador, Michal Hocko,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, fam.zheng, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Tue, Apr 20, 2021 at 7:20 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 4/15/21 1:40 AM, Muchun Song wrote:
> > When we free a HugeTLB page to the buddy allocator, we need to allocate
> > the vmemmap pages associated with it. However, we may not be able to
> > allocate the vmemmap pages when the system is under memory pressure. In
> > this case, we just refuse to free the HugeTLB page. This changes behavior
> > in some corner cases as listed below:
> >
> >  1) Failing to free a huge page triggered by the user (decrease nr_pages).
> >
> >     User needs to try again later.
> >
> >  2) Failing to free a surplus huge page when freed by the application.
> >
> >     Try again later when freeing a huge page next time.
> >
> >  3) Failing to dissolve a free huge page on ZONE_MOVABLE via
> >     offline_pages().
> >
> >     This can happen when we have plenty of ZONE_MOVABLE memory, but
> >     not enough kernel memory to allocate vmemmmap pages.  We may even
> >     be able to migrate huge page contents, but will not be able to
> >     dissolve the source huge page.  This will prevent an offline
> >     operation and is unfortunate as memory offlining is expected to
> >     succeed on movable zones.  Users that depend on memory hotplug
> >     to succeed for movable zones should carefully consider whether the
> >     memory savings gained from this feature are worth the risk of
> >     possibly not being able to offline memory in certain situations.
> >
> >  4) Failing to dissolve a huge page on CMA/ZONE_MOVABLE via
> >     alloc_contig_range() - once we have that handling in place. Mainly
> >     affects CMA and virtio-mem.
> >
> >     Similar to 3). virito-mem will handle migration errors gracefully.
> >     CMA might be able to fallback on other free areas within the CMA
> >     region.
> >
> > Vmemmap pages are allocated from the page freeing context. In order for
> > those allocations to be not disruptive (e.g. trigger oom killer)
> > __GFP_NORETRY is used. hugetlb_lock is dropped for the allocation
> > because a non sleeping allocation would be too fragile and it could fail
> > too easily under memory pressure. GFP_ATOMIC or other modes to access
> > memory reserves is not used because we want to prevent consuming
> > reserves under heavy hugetlb freeing.
> >
> > Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> > ---
> >  Documentation/admin-guide/mm/hugetlbpage.rst    |  8 +++
> >  Documentation/admin-guide/mm/memory-hotplug.rst | 13 ++++
> >  include/linux/hugetlb.h                         |  3 +
> >  include/linux/mm.h                              |  2 +
> >  mm/hugetlb.c                                    | 85 ++++++++++++++++++++-----
> >  mm/hugetlb_vmemmap.c                            | 34 ++++++++++
> >  mm/hugetlb_vmemmap.h                            |  6 ++
> >  mm/sparse-vmemmap.c                             | 75 +++++++++++++++++++++-
> >  8 files changed, 210 insertions(+), 16 deletions(-)
> >
> > diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst
> > index f7b1c7462991..6988895d09a8 100644
> > --- a/Documentation/admin-guide/mm/hugetlbpage.rst
> > +++ b/Documentation/admin-guide/mm/hugetlbpage.rst
> > @@ -60,6 +60,10 @@ HugePages_Surp
> >          the pool above the value in ``/proc/sys/vm/nr_hugepages``. The
> >          maximum number of surplus huge pages is controlled by
> >          ``/proc/sys/vm/nr_overcommit_hugepages``.
> > +     Note: When the feature of freeing unused vmemmap pages associated
> > +     with each hugetlb page is enabled, the number of surplus huge pages
> > +     may be temporarily larger than the maximum number of surplus huge
> > +     pages when the system is under memory pressure.
> >  Hugepagesize
> >       is the default hugepage size (in Kb).
> >  Hugetlb
> > @@ -80,6 +84,10 @@ returned to the huge page pool when freed by a task.  A user with root
> >  privileges can dynamically allocate more or free some persistent huge pages
> >  by increasing or decreasing the value of ``nr_hugepages``.
> >
> > +Note: When the feature of freeing unused vmemmap pages associated with each
> > +hugetlb page is enabled, we can fail to free the huge pages triggered by
> > +the user when ths system is under memory pressure.  Please try again later.
> > +
> >  Pages that are used as huge pages are reserved inside the kernel and cannot
> >  be used for other purposes.  Huge pages cannot be swapped out under
> >  memory pressure.
> > diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
> > index 05d51d2d8beb..c6bae2d77160 100644
> > --- a/Documentation/admin-guide/mm/memory-hotplug.rst
> > +++ b/Documentation/admin-guide/mm/memory-hotplug.rst
> > @@ -357,6 +357,19 @@ creates ZONE_MOVABLE as following.
> >     Unfortunately, there is no information to show which memory block belongs
> >     to ZONE_MOVABLE. This is TBD.
> >
> > +   Memory offlining can fail when dissolving a free huge page on ZONE_MOVABLE
> > +   and the feature of freeing unused vmemmap pages associated with each hugetlb
> > +   page is enabled.
> > +
> > +   This can happen when we have plenty of ZONE_MOVABLE memory, but not enough
> > +   kernel memory to allocate vmemmmap pages.  We may even be able to migrate
> > +   huge page contents, but will not be able to dissolve the source huge page.
> > +   This will prevent an offline operation and is unfortunate as memory offlining
> > +   is expected to succeed on movable zones.  Users that depend on memory hotplug
> > +   to succeed for movable zones should carefully consider whether the memory
> > +   savings gained from this feature are worth the risk of possibly not being
> > +   able to offline memory in certain situations.
> > +
> >  .. note::
> >     Techniques that rely on long-term pinnings of memory (especially, RDMA and
> >     vfio) are fundamentally problematic with ZONE_MOVABLE and, therefore, memory
> > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> > index 0abed7e766b8..6e970a7d3480 100644
> > --- a/include/linux/hugetlb.h
> > +++ b/include/linux/hugetlb.h
> > @@ -525,6 +525,7 @@ unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
> >   *   code knows it has only reference.  All other examinations and
> >   *   modifications require hugetlb_lock.
> >   * HPG_freed - Set when page is on the free lists.
> > + * HPG_vmemmap_optimized - Set when the vmemmap pages of the page are freed.
> >   *   Synchronization: hugetlb_lock held for examination and modification.
>
> I like the per-page flag.  In previous versions of the series, you just
> checked the free_vmemmap_pages_per_hpage() to determine if vmemmmap
> should be allocated.  Is there any change in functionality that makes is
> necessary to set the flag in each page, or is it mostly for flexibility
> going forward?

Actually, only the routine of dissolving the page cares whether
the page is on the buddy free list when update_and_free_page
returns. But we cannot change the return type of the
update_and_free_page (e.g. change return type from 'void' to 'int').
Why? If the hugepage is freed through a kworker, we cannot
know the return value when update_and_free_page returns.
So adding a return value seems odd.

In the dissolving routine, We can allocate vmemmap pages first,
if it is successful, then we can make sure that
update_and_free_page can successfully free page. So I need
some stuff to mark the page which does not need to allocate
vmemmap pages.

On the surface, we seem to have a straightforward method
to do this.

Add a new parameter 'alloc_vmemmap' to update_and_free_page() to
indicate that the caller is already allocated the vmemmap pages.
update_and_free_page() do not need to allocate. Just like below.

   void update_and_free_page(struct hstate *h, struct page *page, bool atomic,
           bool alloc_vmemmap)
   {
       if (alloc_vmemmap)
           // allocate vmemmap pages
   }

But if the page is freed through a kworker. How to pass
'alloc_vmemmap' to the kworker? We can embed this
information into the per-page flag. So if we introduce
HPG_vmemmap_optimized, the parameter of
alloc_vmemmap is also necessary.

So it seems that introducing HPG_vmemmap_optimized is
a good choice.

>
> >   */
> >  enum hugetlb_page_flags {
> > @@ -532,6 +533,7 @@ enum hugetlb_page_flags {
> >       HPG_migratable,
> >       HPG_temporary,
> >       HPG_freed,
> > +     HPG_vmemmap_optimized,
> >       __NR_HPAGEFLAGS,
> >  };
> >
> > @@ -577,6 +579,7 @@ HPAGEFLAG(RestoreReserve, restore_reserve)
> >  HPAGEFLAG(Migratable, migratable)
> >  HPAGEFLAG(Temporary, temporary)
> >  HPAGEFLAG(Freed, freed)
> > +HPAGEFLAG(VmemmapOptimized, vmemmap_optimized)
> >
> >  #ifdef CONFIG_HUGETLB_PAGE
> >
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index a4d160ddb749..d0854828bb9c 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -3048,6 +3048,8 @@ static inline void print_vma_addr(char *prefix, unsigned long rip)
> >
> >  void vmemmap_remap_free(unsigned long start, unsigned long end,
> >                       unsigned long reuse);
> > +int vmemmap_remap_alloc(unsigned long start, unsigned long end,
> > +                     unsigned long reuse, gfp_t gfp_mask);
> >
> >  void *sparse_buffer_alloc(unsigned long size);
> >  struct page * __populate_section_memmap(unsigned long pfn,
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index eeb8f5480170..1c37f0098e00 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -1376,6 +1376,34 @@ static void remove_hugetlb_page(struct hstate *h, struct page *page,
> >       h->nr_huge_pages_node[nid]--;
> >  }
> >
> > +static void add_hugetlb_page(struct hstate *h, struct page *page,
> > +                          bool adjust_surplus)
> > +{
>
> We need to be a bit careful with hugepage specific flags that may be
> set.  The routine remove_hugetlb_page which is called for 'page' before
> this routine will not clear any of the hugepage specific flags.  If the
> calling path goes through free_huge_page, most but not all flags are
> cleared.
>
> We had a discussion about clearing the page->private field in Oscar's
> series.  In the case of 'new' pages we can assume page->private is
> cleared, but perhaps we should not make that assumption here.  Since we
> hope to rarely call this routine, it might be safer to do something
> like:
>
>         set_page_private(page, 0);
>         SetHPageVmemmapOptimized(page);

Agree. Thanks for your reminder. I will fix this.

>
> > +     int nid = page_to_nid(page);
> > +
> > +     lockdep_assert_held(&hugetlb_lock);
> > +
> > +     INIT_LIST_HEAD(&page->lru);
> > +     h->nr_huge_pages++;
> > +     h->nr_huge_pages_node[nid]++;
> > +
> > +     if (adjust_surplus) {
> > +             h->surplus_huge_pages++;
> > +             h->surplus_huge_pages_node[nid]++;
> > +     }
> > +
> > +     set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
> > +
> > +     /*
> > +      * The refcount can possibly be increased by memory-failure or
> > +      * soft_offline handlers.
> > +      */
> > +     if (likely(put_page_testzero(page))) {
>
> In the existing code there is no such test.  Is the need for the test
> because of something introduced in the new code?

No.

> Or, should this test be in the existing code?

Yes. gather_surplus_pages should be fixed. I can fix it
in a separate patch.

The possible bad scenario:

CPU0:                           CPU1:
                                set_compound_page_dtor(HUGETLB_PAGE_DTOR);
memory_failure_hugetlb
  get_hwpoison_page
    __get_hwpoison_page
      get_page_unless_zero
                                put_page_testzero()

  put_page(page)


More details and discussion can refer to:

https://lore.kernel.org/linux-doc/CAMZfGtVRSBkKe=tKAKLY8dp_hywotq3xL+EJZNjXuSKt3HK3bQ@mail.gmail.com/

>
> Sorry, I am not seeing why this is needed.
>
> > +             arch_clear_hugepage_flags(page);
> > +             enqueue_huge_page(h, page);
> > +     }
> > +}
> > +
> >  static void __update_and_free_page(struct hstate *h, struct page *page)
> >  {
> >       int i;
> > @@ -1384,6 +1412,18 @@ static void __update_and_free_page(struct hstate *h, struct page *page)
> >       if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
> >               return;
> >
> > +     if (alloc_huge_page_vmemmap(h, page)) {
> > +             spin_lock_irq(&hugetlb_lock);
> > +             /*
> > +              * If we cannot allocate vmemmap pages, just refuse to free the
> > +              * page and put the page back on the hugetlb free list and treat
> > +              * as a surplus page.
> > +              */
> > +             add_hugetlb_page(h, page, true);
> > +             spin_unlock_irq(&hugetlb_lock);
> > +             return;
> > +     }
> > +
> >       for (i = 0; i < pages_per_huge_page(h);
> >            i++, subpage = mem_map_next(subpage, page, i)) {
> >               subpage->flags &= ~(1 << PG_locked | 1 << PG_error |
> > @@ -1444,7 +1484,7 @@ static inline void flush_free_hpage_work(struct hstate *h)
> >  static void update_and_free_page(struct hstate *h, struct page *page,
> >                                bool atomic)
> >  {
> > -     if (!free_vmemmap_pages_per_hpage(h) || !atomic) {
> > +     if (!HPageVmemmapOptimized(page) || !atomic) {
> >               __update_and_free_page(h, page);
> >               return;
> >       }
>
> When update_and_free_pages_bulk was added it was done to avoid
> lock/unlock cycles with each page.  At the time, I thought about the
> addition of code to allocate vmmemmap, and the possibility that those
> allocations could fail.  I thought it might make sense to perhaps
> process the pages one at a time so that we could quit at the first
> allocation failure.  After more thought, I think it is best to leave the
> code to do bulk operations as you have done above.  Why?
> - Just because one allocation fails does not mean the next will fail.
>   It is possible the allocations could be from different nodes/zones.
> - We will still need to put the requested number of pages into surplus
>   state.
>
> I am not suggesting you change anything.  Just wanted to share my
> thoughts in case someone thought otherwise.
>
> > @@ -1790,10 +1830,14 @@ static struct page *remove_pool_huge_page(struct hstate *h,
> >   * nothing for in-use hugepages and non-hugepages.
> >   * This function returns values like below:
> >   *
> > - *  -EBUSY: failed to dissolved free hugepages or the hugepage is in-use
> > - *          (allocated or reserved.)
> > - *       0: successfully dissolved free hugepages or the page is not a
> > - *          hugepage (considered as already dissolved)
> > + *  -ENOMEM: failed to allocate vmemmap pages to free the freed hugepages
> > + *           when the system is under memory pressure and the feature of
> > + *           freeing unused vmemmap pages associated with each hugetlb page
> > + *           is enabled.
> > + *  -EBUSY:  failed to dissolved free hugepages or the hugepage is in-use
> > + *           (allocated or reserved.)
> > + *       0:  successfully dissolved free hugepages or the page is not a
> > + *           hugepage (considered as already dissolved)
> >   */
> >  int dissolve_free_huge_page(struct page *page)
> >  {
> > @@ -1835,19 +1879,30 @@ int dissolve_free_huge_page(struct page *page)
> >                       goto retry;
> >               }
> >
> > -             /*
> > -              * Move PageHWPoison flag from head page to the raw error page,
> > -              * which makes any subpages rather than the error page reusable.
> > -              */
> > -             if (PageHWPoison(head) && page != head) {
> > -                     SetPageHWPoison(page);
> > -                     ClearPageHWPoison(head);
> > -             }
> >               remove_hugetlb_page(h, page, false);
> >               h->max_huge_pages--;
> >               spin_unlock_irq(&hugetlb_lock);
> > -             update_and_free_page(h, head, false);
> > -             return 0;
> > +
> > +             rc = alloc_huge_page_vmemmap(h, page);
> > +             if (!rc) {
> > +                     /*
> > +                      * Move PageHWPoison flag from head page to the raw
> > +                      * error page, which makes any subpages rather than
> > +                      * the error page reusable.
> > +                      */
> > +                     if (PageHWPoison(head) && page != head) {
> > +                             SetPageHWPoison(page);
> > +                             ClearPageHWPoison(head);
> > +                     }
> > +                     update_and_free_page(h, head, false);
> > +             } else {
> > +                     spin_lock_irq(&hugetlb_lock);
> > +                     add_hugetlb_page(h, page, false);
> > +                     h->max_huge_pages++;
> > +                     spin_unlock_irq(&hugetlb_lock);
> > +             }
> > +
> > +             return rc;
> >       }
> >  out:
> >       spin_unlock_irq(&hugetlb_lock);
>
> Changes in the files below have not changed in any significant way
> since the previous version.  The code looks good to me, but I would
> like to see if there are comments from others.

Thanks for your review. :-)

>
> Thanks,
> --
> Mike Kravetz
>
> > diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> > index cb28c5b6c9ff..a897c7778246 100644
> > --- a/mm/hugetlb_vmemmap.c
> > +++ b/mm/hugetlb_vmemmap.c
> > @@ -185,6 +185,38 @@ static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
> >       return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
> >  }
> >
> > +/*
> > + * Previously discarded vmemmap pages will be allocated and remapping
> > + * after this function returns zero.
> > + */
> > +int alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
> > +{
> > +     int ret;
> > +     unsigned long vmemmap_addr = (unsigned long)head;
> > +     unsigned long vmemmap_end, vmemmap_reuse;
> > +
> > +     if (!HPageVmemmapOptimized(head))
> > +             return 0;
> > +
> > +     vmemmap_addr += RESERVE_VMEMMAP_SIZE;
> > +     vmemmap_end = vmemmap_addr + free_vmemmap_pages_size_per_hpage(h);
> > +     vmemmap_reuse = vmemmap_addr - PAGE_SIZE;
> > +     /*
> > +      * The pages which the vmemmap virtual address range [@vmemmap_addr,
> > +      * @vmemmap_end) are mapped to are freed to the buddy allocator, and
> > +      * the range is mapped to the page which @vmemmap_reuse is mapped to.
> > +      * When a HugeTLB page is freed to the buddy allocator, previously
> > +      * discarded vmemmap pages must be allocated and remapping.
> > +      */
> > +     ret = vmemmap_remap_alloc(vmemmap_addr, vmemmap_end, vmemmap_reuse,
> > +                               GFP_KERNEL | __GFP_NORETRY | __GFP_THISNODE);
> > +
> > +     if (!ret)
> > +             ClearHPageVmemmapOptimized(head);
> > +
> > +     return ret;
> > +}
> > +
> >  void free_huge_page_vmemmap(struct hstate *h, struct page *head)
> >  {
> >       unsigned long vmemmap_addr = (unsigned long)head;
> > @@ -203,4 +235,6 @@ void free_huge_page_vmemmap(struct hstate *h, struct page *head)
> >        * which the range [@vmemmap_addr, @vmemmap_end] is mapped to.
> >        */
> >       vmemmap_remap_free(vmemmap_addr, vmemmap_end, vmemmap_reuse);
> > +
> > +     SetHPageVmemmapOptimized(head);
> >  }
> > diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
> > index 01f8637adbe0..a37771b0b82a 100644
> > --- a/mm/hugetlb_vmemmap.h
> > +++ b/mm/hugetlb_vmemmap.h
> > @@ -11,6 +11,7 @@
> >  #include <linux/hugetlb.h>
> >
> >  #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
> > +int alloc_huge_page_vmemmap(struct hstate *h, struct page *head);
> >  void free_huge_page_vmemmap(struct hstate *h, struct page *head);
> >
> >  /*
> > @@ -25,6 +26,11 @@ static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
> >       return 0;
> >  }
> >  #else
> > +static inline int alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
> > +{
> > +     return 0;
> > +}
> > +
> >  static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head)
> >  {
> >  }
> > diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> > index 7d40b5bd7046..693de0aec7a8 100644
> > --- a/mm/sparse-vmemmap.c
> > +++ b/mm/sparse-vmemmap.c
> > @@ -40,7 +40,8 @@
> >   * @remap_pte:               called for each lowest-level entry (PTE).
> >   * @reuse_page:              the page which is reused for the tail vmemmap pages.
> >   * @reuse_addr:              the virtual address of the @reuse_page page.
> > - * @vmemmap_pages:   the list head of the vmemmap pages that can be freed.
> > + * @vmemmap_pages:   the list head of the vmemmap pages that can be freed
> > + *                   or is mapped from.
> >   */
> >  struct vmemmap_remap_walk {
> >       void (*remap_pte)(pte_t *pte, unsigned long addr,
> > @@ -224,6 +225,78 @@ void vmemmap_remap_free(unsigned long start, unsigned long end,
> >       free_vmemmap_page_list(&vmemmap_pages);
> >  }
> >
> > +static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
> > +                             struct vmemmap_remap_walk *walk)
> > +{
> > +     pgprot_t pgprot = PAGE_KERNEL;
> > +     struct page *page;
> > +     void *to;
> > +
> > +     BUG_ON(pte_page(*pte) != walk->reuse_page);
> > +
> > +     page = list_first_entry(walk->vmemmap_pages, struct page, lru);
> > +     list_del(&page->lru);
> > +     to = page_to_virt(page);
> > +     copy_page(to, (void *)walk->reuse_addr);
> > +
> > +     set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot));
> > +}
> > +
> > +static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
> > +                                gfp_t gfp_mask, struct list_head *list)
> > +{
> > +     unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
> > +     int nid = page_to_nid((struct page *)start);
> > +     struct page *page, *next;
> > +
> > +     while (nr_pages--) {
> > +             page = alloc_pages_node(nid, gfp_mask, 0);
> > +             if (!page)
> > +                     goto out;
> > +             list_add_tail(&page->lru, list);
> > +     }
> > +
> > +     return 0;
> > +out:
> > +     list_for_each_entry_safe(page, next, list, lru)
> > +             __free_pages(page, 0);
> > +     return -ENOMEM;
> > +}
> > +
> > +/**
> > + * vmemmap_remap_alloc - remap the vmemmap virtual address range [@start, end)
> > + *                    to the page which is from the @vmemmap_pages
> > + *                    respectively.
> > + * @start:   start address of the vmemmap virtual address range that we want
> > + *           to remap.
> > + * @end:     end address of the vmemmap virtual address range that we want to
> > + *           remap.
> > + * @reuse:   reuse address.
> > + * @gpf_mask:        GFP flag for allocating vmemmap pages.
> > + */
> > +int vmemmap_remap_alloc(unsigned long start, unsigned long end,
> > +                     unsigned long reuse, gfp_t gfp_mask)
> > +{
> > +     LIST_HEAD(vmemmap_pages);
> > +     struct vmemmap_remap_walk walk = {
> > +             .remap_pte      = vmemmap_restore_pte,
> > +             .reuse_addr     = reuse,
> > +             .vmemmap_pages  = &vmemmap_pages,
> > +     };
> > +
> > +     /* See the comment in the vmemmap_remap_free(). */
> > +     BUG_ON(start - reuse != PAGE_SIZE);
> > +
> > +     might_sleep_if(gfpflags_allow_blocking(gfp_mask));
> > +
> > +     if (alloc_vmemmap_page_list(start, end, gfp_mask, &vmemmap_pages))
> > +             return -ENOMEM;
> > +
> > +     vmemmap_remap_range(reuse, end, &walk);
> > +
> > +     return 0;
> > +}
> > +
> >  /*
> >   * Allocate a block of memory to be used to back the virtual memory map
> >   * or to back the page tables that are used to create the mapping.
> >

^ permalink raw reply	[flat|nested] 24+ messages in thread

* Re: [PATCH v20 8/9] mm: memory_hotplug: disable memmap_on_memory when hugetlb_free_vmemmap enabled
  2021-04-15  8:40 ` [PATCH v20 8/9] mm: memory_hotplug: disable memmap_on_memory when hugetlb_free_vmemmap enabled Muchun Song
@ 2021-04-20 10:35   ` Oscar Salvador
  2021-04-21  3:41     ` [External] " Muchun Song
  0 siblings, 1 reply; 24+ messages in thread
From: Oscar Salvador @ 2021-04-20 10:35 UTC (permalink / raw)
  To: Muchun Song
  Cc: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, pawan.kumar.gupta, rdunlap,
	oneukum, anshuman.khandual, jroedel, almasrymina, rientjes,
	willy, mhocko, song.bao.hua, david, naoya.horiguchi,
	joao.m.martins, duanxiongchun, fam.zheng, linux-doc,
	linux-kernel, linux-mm, linux-fsdevel

On Thu, Apr 15, 2021 at 04:40:04PM +0800, Muchun Song wrote:
>  bool mhp_supports_memmap_on_memory(unsigned long size)
>  {
> +	bool supported;
>  	unsigned long nr_vmemmap_pages = size / PAGE_SIZE;
>  	unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page);
>  	unsigned long remaining_size = size - vmemmap_size;
> @@ -1011,11 +1012,18 @@ bool mhp_supports_memmap_on_memory(unsigned long size)
>  	 *	 altmap as an alternative source of memory, and we do not exactly
>  	 *	 populate a single PMD.
>  	 */
> -	return memmap_on_memory &&
> -	       IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) &&
> -	       size == memory_block_size_bytes() &&
> -	       IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
> -	       IS_ALIGNED(remaining_size, pageblock_nr_pages << PAGE_SHIFT);
> +	supported = memmap_on_memory &&
> +		    IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) &&
> +		    size == memory_block_size_bytes() &&
> +		    IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
> +		    IS_ALIGNED(remaining_size, pageblock_nr_pages << PAGE_SHIFT);
> +
> +	if (supported && is_hugetlb_free_vmemmap_enabled()) {
> +		pr_info("Cannot enable memory_hotplug.memmap_on_memory, it is not compatible with hugetlb_free_vmemmap\n");
> +		supported = false;
> +	}

I would not print anything and rather have

return memmap_on_memory &&
       !is_hugetlb_free_vmemmap_enabled &&
       IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) &&
       size == memory_block_size_bytes() &&
       IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
       IS_ALIGNED(remaining_size, pageblock_nr_pages << PAGE_SHIFT);

Documentation/admin-guide/kernel-parameters.txt already provides an
explanation on memory_hotplug.memmap_on_memory parameter that states
that the feature cannot be enabled when using hugetlb-vmemmap
optimization.

Users can always check whether the feature is enabled via
/sys/modules/memory_hotplug/parameters/memmap_on_memory.

Also, I did not check if it is, but if not, the fact about hugetlb-vmemmmap vs
hotplug-vmemmap should also be called out in the hugetlb-vmemmap kernel
parameter.

Thanks

-- 
Oscar Salvador
SUSE L3

^ permalink raw reply	[flat|nested] 24+ messages in thread

* Re: [External] Re: [PATCH v20 6/9] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-04-20  8:46     ` [External] " Muchun Song
@ 2021-04-20 17:48       ` Mike Kravetz
  2021-04-21  3:42         ` Muchun Song
  0 siblings, 1 reply; 24+ messages in thread
From: Mike Kravetz @ 2021-04-20 17:48 UTC (permalink / raw)
  To: Muchun Song
  Cc: Jonathan Corbet, Thomas Gleixner, Ingo Molnar, bp, X86 ML, hpa,
	dave.hansen, luto, Peter Zijlstra, Alexander Viro, Andrew Morton,
	paulmck, pawan.kumar.gupta, Randy Dunlap, oneukum,
	anshuman.khandual, jroedel, Mina Almasry, David Rientjes,
	Matthew Wilcox, Oscar Salvador, Michal Hocko,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, fam.zheng, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On 4/20/21 1:46 AM, Muchun Song wrote:
> On Tue, Apr 20, 2021 at 7:20 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>>
>> On 4/15/21 1:40 AM, Muchun Song wrote:
>>> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
>>> index 0abed7e766b8..6e970a7d3480 100644
>>> --- a/include/linux/hugetlb.h
>>> +++ b/include/linux/hugetlb.h
>>> @@ -525,6 +525,7 @@ unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
>>>   *   code knows it has only reference.  All other examinations and
>>>   *   modifications require hugetlb_lock.
>>>   * HPG_freed - Set when page is on the free lists.
>>> + * HPG_vmemmap_optimized - Set when the vmemmap pages of the page are freed.
>>>   *   Synchronization: hugetlb_lock held for examination and modification.
>>
>> I like the per-page flag.  In previous versions of the series, you just
>> checked the free_vmemmap_pages_per_hpage() to determine if vmemmmap
>> should be allocated.  Is there any change in functionality that makes is
>> necessary to set the flag in each page, or is it mostly for flexibility
>> going forward?
> 
> Actually, only the routine of dissolving the page cares whether
> the page is on the buddy free list when update_and_free_page
> returns. But we cannot change the return type of the
> update_and_free_page (e.g. change return type from 'void' to 'int').
> Why? If the hugepage is freed through a kworker, we cannot
> know the return value when update_and_free_page returns.
> So adding a return value seems odd.
> 
> In the dissolving routine, We can allocate vmemmap pages first,
> if it is successful, then we can make sure that
> update_and_free_page can successfully free page. So I need
> some stuff to mark the page which does not need to allocate
> vmemmap pages.
> 
> On the surface, we seem to have a straightforward method
> to do this.
> 
> Add a new parameter 'alloc_vmemmap' to update_and_free_page() to
> indicate that the caller is already allocated the vmemmap pages.
> update_and_free_page() do not need to allocate. Just like below.
> 
>    void update_and_free_page(struct hstate *h, struct page *page, bool atomic,
>            bool alloc_vmemmap)
>    {
>        if (alloc_vmemmap)
>            // allocate vmemmap pages
>    }
> 
> But if the page is freed through a kworker. How to pass
> 'alloc_vmemmap' to the kworker? We can embed this
> information into the per-page flag. So if we introduce
> HPG_vmemmap_optimized, the parameter of
> alloc_vmemmap is also necessary.
> 
> So it seems that introducing HPG_vmemmap_optimized is
> a good choice.

Thanks for the explanation!

Agree that the flag is a good choice.  How about adding a comment like
this above the alloc_huge_page_vmemmap call in dissolve_free_huge_page?

/*
 * Normally update_and_free_page will allocate required vmemmmap before
 * freeing the page.  update_and_free_page will fail to free the page
 * if it can not allocate required vmemmap.  We need to adjust
 * max_huge_pages if the page is not freed.  Attempt to allocate
 * vmemmmap here so that we can take appropriate action on failure.
 */

...
>>> +static void add_hugetlb_page(struct hstate *h, struct page *page,
>>> +                          bool adjust_surplus)
>>> +{
>>
>> We need to be a bit careful with hugepage specific flags that may be
>> set.  The routine remove_hugetlb_page which is called for 'page' before
>> this routine will not clear any of the hugepage specific flags.  If the
>> calling path goes through free_huge_page, most but not all flags are
>> cleared.
>>
>> We had a discussion about clearing the page->private field in Oscar's
>> series.  In the case of 'new' pages we can assume page->private is
>> cleared, but perhaps we should not make that assumption here.  Since we
>> hope to rarely call this routine, it might be safer to do something
>> like:
>>
>>         set_page_private(page, 0);
>>         SetHPageVmemmapOptimized(page);
> 
> Agree. Thanks for your reminder. I will fix this.
> 
>>
>>> +     int nid = page_to_nid(page);
>>> +
>>> +     lockdep_assert_held(&hugetlb_lock);
>>> +
>>> +     INIT_LIST_HEAD(&page->lru);
>>> +     h->nr_huge_pages++;
>>> +     h->nr_huge_pages_node[nid]++;
>>> +
>>> +     if (adjust_surplus) {
>>> +             h->surplus_huge_pages++;
>>> +             h->surplus_huge_pages_node[nid]++;
>>> +     }
>>> +
>>> +     set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
>>> +
>>> +     /*
>>> +      * The refcount can possibly be increased by memory-failure or
>>> +      * soft_offline handlers.
>>> +      */
>>> +     if (likely(put_page_testzero(page))) {
>>
>> In the existing code there is no such test.  Is the need for the test
>> because of something introduced in the new code?
> 
> No.
> 
>> Or, should this test be in the existing code?
> 
> Yes. gather_surplus_pages should be fixed. I can fix it
> in a separate patch.
> 
> The possible bad scenario:
> 
> CPU0:                           CPU1:
>                                 set_compound_page_dtor(HUGETLB_PAGE_DTOR);
> memory_failure_hugetlb
>   get_hwpoison_page
>     __get_hwpoison_page
>       get_page_unless_zero
>                                 put_page_testzero()
> 
>   put_page(page)
> 
> 
> More details and discussion can refer to:
> 
> https://lore.kernel.org/linux-doc/CAMZfGtVRSBkKe=tKAKLY8dp_hywotq3xL+EJZNjXuSKt3HK3bQ@mail.gmail.com/
> 

Thanks you!  I did not remember that discussion.

It would be helpful to add a separate patch for gather_surplus_pages.
Otherwise, we have the VM_BUG_ON there and not in add_hugetlb_page.

-- 
Mike Kravetz

^ permalink raw reply	[flat|nested] 24+ messages in thread

* Re: [External] Re: [PATCH v20 8/9] mm: memory_hotplug: disable memmap_on_memory when hugetlb_free_vmemmap enabled
  2021-04-20 10:35   ` Oscar Salvador
@ 2021-04-21  3:41     ` Muchun Song
  2021-04-21  7:33       ` Oscar Salvador
  0 siblings, 1 reply; 24+ messages in thread
From: Muchun Song @ 2021-04-21  3:41 UTC (permalink / raw)
  To: Oscar Salvador
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, Ingo Molnar, bp,
	X86 ML, hpa, dave.hansen, luto, Peter Zijlstra, Alexander Viro,
	Andrew Morton, paulmck, pawan.kumar.gupta, Randy Dunlap, oneukum,
	anshuman.khandual, jroedel, Mina Almasry, David Rientjes,
	Matthew Wilcox, Michal Hocko, Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, fam.zheng, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Tue, Apr 20, 2021 at 6:35 PM Oscar Salvador <osalvador@suse.de> wrote:
>
> On Thu, Apr 15, 2021 at 04:40:04PM +0800, Muchun Song wrote:
> >  bool mhp_supports_memmap_on_memory(unsigned long size)
> >  {
> > +     bool supported;
> >       unsigned long nr_vmemmap_pages = size / PAGE_SIZE;
> >       unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page);
> >       unsigned long remaining_size = size - vmemmap_size;
> > @@ -1011,11 +1012,18 @@ bool mhp_supports_memmap_on_memory(unsigned long size)
> >        *       altmap as an alternative source of memory, and we do not exactly
> >        *       populate a single PMD.
> >        */
> > -     return memmap_on_memory &&
> > -            IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) &&
> > -            size == memory_block_size_bytes() &&
> > -            IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
> > -            IS_ALIGNED(remaining_size, pageblock_nr_pages << PAGE_SHIFT);
> > +     supported = memmap_on_memory &&
> > +                 IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) &&
> > +                 size == memory_block_size_bytes() &&
> > +                 IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
> > +                 IS_ALIGNED(remaining_size, pageblock_nr_pages << PAGE_SHIFT);
> > +
> > +     if (supported && is_hugetlb_free_vmemmap_enabled()) {
> > +             pr_info("Cannot enable memory_hotplug.memmap_on_memory, it is not compatible with hugetlb_free_vmemmap\n");
> > +             supported = false;
> > +     }
>
> I would not print anything and rather have
>
> return memmap_on_memory &&
>        !is_hugetlb_free_vmemmap_enabled &&
>        IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) &&
>        size == memory_block_size_bytes() &&
>        IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
>        IS_ALIGNED(remaining_size, pageblock_nr_pages << PAGE_SHIFT);

OK. Will do.

>
> Documentation/admin-guide/kernel-parameters.txt already provides an
> explanation on memory_hotplug.memmap_on_memory parameter that states
> that the feature cannot be enabled when using hugetlb-vmemmap
> optimization.
>
> Users can always check whether the feature is enabled via
> /sys/modules/memory_hotplug/parameters/memmap_on_memory.

If memory_hotplug.memmap_on_memory is enabled

    $ cat /sys/module/memory_hotplug/parameters/memmap_on_memory
    $ Y

If memory_hotplug.memmap_on_memory is disabled

    $ cat /sys/module/memory_hotplug/parameters/memmap_on_memory
    $ N

>
> Also, I did not check if it is, but if not, the fact about hugetlb-vmemmmap vs
> hotplug-vmemmap should also be called out in the hugetlb-vmemmap kernel
> parameter.

Make sense. I will update the doc.

Thanks.

>
> Thanks
>
> --
> Oscar Salvador
> SUSE L3

^ permalink raw reply	[flat|nested] 24+ messages in thread

* Re: [External] Re: [PATCH v20 6/9] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-04-20 17:48       ` Mike Kravetz
@ 2021-04-21  3:42         ` Muchun Song
  0 siblings, 0 replies; 24+ messages in thread
From: Muchun Song @ 2021-04-21  3:42 UTC (permalink / raw)
  To: Mike Kravetz
  Cc: Jonathan Corbet, Thomas Gleixner, Ingo Molnar, bp, X86 ML, hpa,
	dave.hansen, luto, Peter Zijlstra, Alexander Viro, Andrew Morton,
	paulmck, pawan.kumar.gupta, Randy Dunlap, oneukum,
	anshuman.khandual, jroedel, Mina Almasry, David Rientjes,
	Matthew Wilcox, Oscar Salvador, Michal Hocko,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, fam.zheng, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Wed, Apr 21, 2021 at 1:48 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 4/20/21 1:46 AM, Muchun Song wrote:
> > On Tue, Apr 20, 2021 at 7:20 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
> >>
> >> On 4/15/21 1:40 AM, Muchun Song wrote:
> >>> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> >>> index 0abed7e766b8..6e970a7d3480 100644
> >>> --- a/include/linux/hugetlb.h
> >>> +++ b/include/linux/hugetlb.h
> >>> @@ -525,6 +525,7 @@ unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
> >>>   *   code knows it has only reference.  All other examinations and
> >>>   *   modifications require hugetlb_lock.
> >>>   * HPG_freed - Set when page is on the free lists.
> >>> + * HPG_vmemmap_optimized - Set when the vmemmap pages of the page are freed.
> >>>   *   Synchronization: hugetlb_lock held for examination and modification.
> >>
> >> I like the per-page flag.  In previous versions of the series, you just
> >> checked the free_vmemmap_pages_per_hpage() to determine if vmemmmap
> >> should be allocated.  Is there any change in functionality that makes is
> >> necessary to set the flag in each page, or is it mostly for flexibility
> >> going forward?
> >
> > Actually, only the routine of dissolving the page cares whether
> > the page is on the buddy free list when update_and_free_page
> > returns. But we cannot change the return type of the
> > update_and_free_page (e.g. change return type from 'void' to 'int').
> > Why? If the hugepage is freed through a kworker, we cannot
> > know the return value when update_and_free_page returns.
> > So adding a return value seems odd.
> >
> > In the dissolving routine, We can allocate vmemmap pages first,
> > if it is successful, then we can make sure that
> > update_and_free_page can successfully free page. So I need
> > some stuff to mark the page which does not need to allocate
> > vmemmap pages.
> >
> > On the surface, we seem to have a straightforward method
> > to do this.
> >
> > Add a new parameter 'alloc_vmemmap' to update_and_free_page() to
> > indicate that the caller is already allocated the vmemmap pages.
> > update_and_free_page() do not need to allocate. Just like below.
> >
> >    void update_and_free_page(struct hstate *h, struct page *page, bool atomic,
> >            bool alloc_vmemmap)
> >    {
> >        if (alloc_vmemmap)
> >            // allocate vmemmap pages
> >    }
> >
> > But if the page is freed through a kworker. How to pass
> > 'alloc_vmemmap' to the kworker? We can embed this
> > information into the per-page flag. So if we introduce
> > HPG_vmemmap_optimized, the parameter of
> > alloc_vmemmap is also necessary.
> >
> > So it seems that introducing HPG_vmemmap_optimized is
> > a good choice.
>
> Thanks for the explanation!
>
> Agree that the flag is a good choice.  How about adding a comment like
> this above the alloc_huge_page_vmemmap call in dissolve_free_huge_page?
>
> /*
>  * Normally update_and_free_page will allocate required vmemmmap before
>  * freeing the page.  update_and_free_page will fail to free the page
>  * if it can not allocate required vmemmap.  We need to adjust
>  * max_huge_pages if the page is not freed.  Attempt to allocate
>  * vmemmmap here so that we can take appropriate action on failure.
>  */

Thanks. I will add this comment.

>
> ...
> >>> +static void add_hugetlb_page(struct hstate *h, struct page *page,
> >>> +                          bool adjust_surplus)
> >>> +{
> >>
> >> We need to be a bit careful with hugepage specific flags that may be
> >> set.  The routine remove_hugetlb_page which is called for 'page' before
> >> this routine will not clear any of the hugepage specific flags.  If the
> >> calling path goes through free_huge_page, most but not all flags are
> >> cleared.
> >>
> >> We had a discussion about clearing the page->private field in Oscar's
> >> series.  In the case of 'new' pages we can assume page->private is
> >> cleared, but perhaps we should not make that assumption here.  Since we
> >> hope to rarely call this routine, it might be safer to do something
> >> like:
> >>
> >>         set_page_private(page, 0);
> >>         SetHPageVmemmapOptimized(page);
> >
> > Agree. Thanks for your reminder. I will fix this.
> >
> >>
> >>> +     int nid = page_to_nid(page);
> >>> +
> >>> +     lockdep_assert_held(&hugetlb_lock);
> >>> +
> >>> +     INIT_LIST_HEAD(&page->lru);
> >>> +     h->nr_huge_pages++;
> >>> +     h->nr_huge_pages_node[nid]++;
> >>> +
> >>> +     if (adjust_surplus) {
> >>> +             h->surplus_huge_pages++;
> >>> +             h->surplus_huge_pages_node[nid]++;
> >>> +     }
> >>> +
> >>> +     set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
> >>> +
> >>> +     /*
> >>> +      * The refcount can possibly be increased by memory-failure or
> >>> +      * soft_offline handlers.
> >>> +      */
> >>> +     if (likely(put_page_testzero(page))) {
> >>
> >> In the existing code there is no such test.  Is the need for the test
> >> because of something introduced in the new code?
> >
> > No.
> >
> >> Or, should this test be in the existing code?
> >
> > Yes. gather_surplus_pages should be fixed. I can fix it
> > in a separate patch.
> >
> > The possible bad scenario:
> >
> > CPU0:                           CPU1:
> >                                 set_compound_page_dtor(HUGETLB_PAGE_DTOR);
> > memory_failure_hugetlb
> >   get_hwpoison_page
> >     __get_hwpoison_page
> >       get_page_unless_zero
> >                                 put_page_testzero()
> >
> >   put_page(page)
> >
> >
> > More details and discussion can refer to:
> >
> > https://lore.kernel.org/linux-doc/CAMZfGtVRSBkKe=tKAKLY8dp_hywotq3xL+EJZNjXuSKt3HK3bQ@mail.gmail.com/
> >
>
> Thanks you!  I did not remember that discussion.
>
> It would be helpful to add a separate patch for gather_surplus_pages.
> Otherwise, we have the VM_BUG_ON there and not in add_hugetlb_page.
>

Agree. Will do.

> --
> Mike Kravetz

^ permalink raw reply	[flat|nested] 24+ messages in thread

* Re: [External] Re: [PATCH v20 8/9] mm: memory_hotplug: disable memmap_on_memory when hugetlb_free_vmemmap enabled
  2021-04-21  3:41     ` [External] " Muchun Song
@ 2021-04-21  7:33       ` Oscar Salvador
  2021-04-21  9:06         ` Muchun Song
  0 siblings, 1 reply; 24+ messages in thread
From: Oscar Salvador @ 2021-04-21  7:33 UTC (permalink / raw)
  To: Muchun Song
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, Ingo Molnar, bp,
	X86 ML, hpa, dave.hansen, luto, Peter Zijlstra, Alexander Viro,
	Andrew Morton, paulmck, pawan.kumar.gupta, Randy Dunlap, oneukum,
	anshuman.khandual, jroedel, Mina Almasry, David Rientjes,
	Matthew Wilcox, Michal Hocko, Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, fam.zheng, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Wed, Apr 21, 2021 at 11:41:24AM +0800, Muchun Song wrote:
> > Documentation/admin-guide/kernel-parameters.txt already provides an
> > explanation on memory_hotplug.memmap_on_memory parameter that states
> > that the feature cannot be enabled when using hugetlb-vmemmap
> > optimization.
> >
> > Users can always check whether the feature is enabled via
> > /sys/modules/memory_hotplug/parameters/memmap_on_memory.

Heh, I realized this is not completely true.
Users can check whether the feature is __enabled__ by checking the sys fs,
but although it is enabled, it might not be effective.

This might be due to a different number of reasons, vmemmap does not fully
span a PMD, the size we want to add spans more than a single memory block, etc.

That is what

"Note that even when enabled, there are a few cases where the feature is not
 effective."

is supposed to mean.

Anyway, I did not change my opionion on this.

Thanks

-- 
Oscar Salvador
SUSE L3

^ permalink raw reply	[flat|nested] 24+ messages in thread

* Re: [External] Re: [PATCH v20 8/9] mm: memory_hotplug: disable memmap_on_memory when hugetlb_free_vmemmap enabled
  2021-04-21  7:33       ` Oscar Salvador
@ 2021-04-21  9:06         ` Muchun Song
  0 siblings, 0 replies; 24+ messages in thread
From: Muchun Song @ 2021-04-21  9:06 UTC (permalink / raw)
  To: Oscar Salvador
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, Ingo Molnar, bp,
	X86 ML, hpa, dave.hansen, luto, Peter Zijlstra, Alexander Viro,
	Andrew Morton, paulmck, pawan.kumar.gupta, Randy Dunlap, oneukum,
	anshuman.khandual, jroedel, Mina Almasry, David Rientjes,
	Matthew Wilcox, Michal Hocko, Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, fam.zheng, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Wed, Apr 21, 2021 at 3:33 PM Oscar Salvador <osalvador@suse.de> wrote:
>
> On Wed, Apr 21, 2021 at 11:41:24AM +0800, Muchun Song wrote:
> > > Documentation/admin-guide/kernel-parameters.txt already provides an
> > > explanation on memory_hotplug.memmap_on_memory parameter that states
> > > that the feature cannot be enabled when using hugetlb-vmemmap
> > > optimization.
> > >
> > > Users can always check whether the feature is enabled via
> > > /sys/modules/memory_hotplug/parameters/memmap_on_memory.
>
> Heh, I realized this is not completely true.
> Users can check whether the feature is __enabled__ by checking the sys fs,
> but although it is enabled, it might not be effective.

Right. I have done the test.

>
> This might be due to a different number of reasons, vmemmap does not fully
> span a PMD, the size we want to add spans more than a single memory block, etc.

Agree. Thanks for your explanations.

>
> That is what
>
> "Note that even when enabled, there are a few cases where the feature is not
>  effective."
>
> is supposed to mean.
>
> Anyway, I did not change my opionion on this.
>
> Thanks
>
> --
> Oscar Salvador
> SUSE L3

^ permalink raw reply	[flat|nested] 24+ messages in thread

end of thread, back to index

Thread overview: 24+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-04-15  8:39 [PATCH v20 0/9] Free some vmemmap pages of HugeTLB page Muchun Song
2021-04-15  8:39 ` [PATCH v20 1/9] mm: memory_hotplug: factor out bootmem core functions to bootmem_info.c Muchun Song
2021-04-15  8:39 ` [PATCH v20 2/9] mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
2021-04-15  8:39 ` [PATCH v20 3/9] mm: hugetlb: gather discrete indexes of tail page Muchun Song
2021-04-16 18:54   ` Mike Kravetz
2021-04-15  8:40 ` [PATCH v20 4/9] mm: hugetlb: free the vmemmap pages associated with each HugeTLB page Muchun Song
2021-04-16 21:10   ` Mike Kravetz
2021-04-17  2:55     ` [External] " Muchun Song
2021-04-15  8:40 ` [PATCH v20 5/9] mm: hugetlb: defer freeing of HugeTLB pages Muchun Song
2021-04-16 23:55   ` Mike Kravetz
2021-04-17  4:13     ` [External] " Muchun Song
2021-04-15  8:40 ` [PATCH v20 6/9] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page Muchun Song
2021-04-19 23:19   ` Mike Kravetz
2021-04-20  8:46     ` [External] " Muchun Song
2021-04-20 17:48       ` Mike Kravetz
2021-04-21  3:42         ` Muchun Song
2021-04-15  8:40 ` [PATCH v20 7/9] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap Muchun Song
2021-04-19 23:41   ` Mike Kravetz
2021-04-15  8:40 ` [PATCH v20 8/9] mm: memory_hotplug: disable memmap_on_memory when hugetlb_free_vmemmap enabled Muchun Song
2021-04-20 10:35   ` Oscar Salvador
2021-04-21  3:41     ` [External] " Muchun Song
2021-04-21  7:33       ` Oscar Salvador
2021-04-21  9:06         ` Muchun Song
2021-04-15  8:40 ` [PATCH v20 9/9] mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate Muchun Song

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