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* [PATCH v15 0/8] Free some vmemmap pages of HugeTLB page
@ 2021-02-08  8:50 Muchun Song
  2021-02-08  8:50 ` [PATCH v15 1/8] mm: memory_hotplug: factor out bootmem core functions to bootmem_info.c Muchun Song
                   ` (7 more replies)
  0 siblings, 8 replies; 37+ messages in thread
From: Muchun Song @ 2021-02-08  8:50 UTC (permalink / raw)
  To: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, mchehab+huawei,
	pawan.kumar.gupta, rdunlap, oneukum, anshuman.khandual, jroedel,
	almasrymina, rientjes, willy, osalvador, mhocko, song.bao.hua,
	david, naoya.horiguchi, joao.m.martins
  Cc: duanxiongchun, linux-doc, linux-kernel, linux-mm, linux-fsdevel,
	Muchun Song

Hi all,

This patch series will free some vmemmap pages(struct page structures)
associated with each hugetlbpage 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 accutualy eliminate 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 a 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 hugetlbpage. 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[0], but with that in added it shows even more:

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

[0] 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 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 (8):
  mm: memory_hotplug: factor out bootmem core functions to
    bootmem_info.c
  mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP
  mm: hugetlb: free the vmemmap pages associated with each HugeTLB page
  mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap
  mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate
  mm: hugetlb: gather discrete indexes of tail page
  mm: hugetlb: optimize the code with the help of the compiler

 Documentation/admin-guide/kernel-parameters.txt |  14 ++
 Documentation/admin-guide/mm/hugetlbpage.rst    |   3 +
 arch/x86/mm/init_64.c                           |  13 +-
 fs/Kconfig                                      |   6 +
 include/linux/bootmem_info.h                    |  65 +++++
 include/linux/hugetlb.h                         |  43 +++-
 include/linux/hugetlb_cgroup.h                  |  19 +-
 include/linux/memory_hotplug.h                  |  27 --
 include/linux/mm.h                              |   5 +
 mm/Makefile                                     |   2 +
 mm/bootmem_info.c                               | 124 ++++++++++
 mm/hugetlb.c                                    |  23 +-
 mm/hugetlb_vmemmap.c                            | 314 ++++++++++++++++++++++++
 mm/hugetlb_vmemmap.h                            |  31 +++
 mm/memory_hotplug.c                             | 116 ---------
 mm/sparse-vmemmap.c                             | 280 +++++++++++++++++++++
 mm/sparse.c                                     |   1 +
 17 files changed, 928 insertions(+), 158 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] 37+ messages in thread

* [PATCH v15 1/8] mm: memory_hotplug: factor out bootmem core functions to bootmem_info.c
  2021-02-08  8:50 [PATCH v15 0/8] Free some vmemmap pages of HugeTLB page Muchun Song
@ 2021-02-08  8:50 ` Muchun Song
  2021-02-08  8:50 ` [PATCH v15 2/8] mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
                   ` (6 subsequent siblings)
  7 siblings, 0 replies; 37+ messages in thread
From: Muchun Song @ 2021-02-08  8:50 UTC (permalink / raw)
  To: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, mchehab+huawei,
	pawan.kumar.gupta, rdunlap, oneukum, anshuman.khandual, jroedel,
	almasrymina, rientjes, willy, osalvador, mhocko, song.bao.hua,
	david, naoya.horiguchi, joao.m.martins
  Cc: duanxiongchun, linux-doc, linux-kernel, linux-mm, linux-fsdevel,
	Muchun Song, Miaohe Lin

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>
---
 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              | 124 +++++++++++++++++++++++++++++++++++++++++
 mm/memory_hotplug.c            | 116 --------------------------------------
 mm/sparse.c                    |   1 +
 7 files changed, 168 insertions(+), 144 deletions(-)
 create mode 100644 include/linux/bootmem_info.h
 create mode 100644 mm/bootmem_info.c

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index b5a3fa4033d3..0a45f062826e 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>
@@ -1571,7 +1572,7 @@ 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 7288aa5ef73b..96659a8b9d02 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. */
@@ -210,17 +198,6 @@ 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);
 
@@ -248,10 +225,6 @@ 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 b2a564eec27f..ce4ddbe4461d 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -83,6 +83,7 @@ obj-$(CONFIG_SLUB) += slub.o
 obj-$(CONFIG_KASAN)	+= kasan/
 obj-$(CONFIG_KFENCE) += kfence/
 obj-$(CONFIG_FAILSLAB) += failslab.o
+obj-$(CONFIG_HAVE_BOOTMEM_INFO_NODE) += bootmem_info.o
 obj-$(CONFIG_MEMORY_HOTPLUG) += memory_hotplug.o
 obj-$(CONFIG_MEMTEST)		+= memtest.o
 obj-$(CONFIG_MIGRATION) += migrate.o
diff --git a/mm/bootmem_info.c b/mm/bootmem_info.c
new file mode 100644
index 000000000000..fcab5a3f8cc0
--- /dev/null
+++ b/mm/bootmem_info.c
@@ -0,0 +1,124 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/mm/bootmem_info.c
+ *
+ *  Copyright (C)
+ */
+#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 5ba51a8bdaeb..a2a72b617040 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -144,122 +144,6 @@ 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 7bd23f9d6cef..87676bf3af40 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 related	[flat|nested] 37+ messages in thread

* [PATCH v15 2/8] mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP
  2021-02-08  8:50 [PATCH v15 0/8] Free some vmemmap pages of HugeTLB page Muchun Song
  2021-02-08  8:50 ` [PATCH v15 1/8] mm: memory_hotplug: factor out bootmem core functions to bootmem_info.c Muchun Song
@ 2021-02-08  8:50 ` Muchun Song
  2021-02-08  8:50 ` [PATCH v15 3/8] mm: hugetlb: free the vmemmap pages associated with each HugeTLB page Muchun Song
                   ` (5 subsequent siblings)
  7 siblings, 0 replies; 37+ messages in thread
From: Muchun Song @ 2021-02-08  8:50 UTC (permalink / raw)
  To: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, mchehab+huawei,
	pawan.kumar.gupta, rdunlap, oneukum, anshuman.khandual, jroedel,
	almasrymina, rientjes, willy, osalvador, mhocko, song.bao.hua,
	david, naoya.horiguchi, joao.m.martins
  Cc: duanxiongchun, linux-doc, linux-kernel, linux-mm, linux-fsdevel,
	Muchun Song, Miaohe Lin

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.

Like other code which frees vmemmap, this config option depends on
HAVE_BOOTMEM_INFO_NODE. 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>
---
 arch/x86/mm/init_64.c | 2 +-
 fs/Kconfig            | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 0a45f062826e..0435bee2e172 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1225,7 +1225,7 @@ 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 97e7b77c9309..de87f234f1e9 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -237,6 +237,12 @@ 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
+	depends on HAVE_BOOTMEM_INFO_NODE
+
 config MEMFD_CREATE
 	def_bool TMPFS || HUGETLBFS
 
-- 
2.11.0



^ permalink raw reply related	[flat|nested] 37+ messages in thread

* [PATCH v15 3/8] mm: hugetlb: free the vmemmap pages associated with each HugeTLB page
  2021-02-08  8:50 [PATCH v15 0/8] Free some vmemmap pages of HugeTLB page Muchun Song
  2021-02-08  8:50 ` [PATCH v15 1/8] mm: memory_hotplug: factor out bootmem core functions to bootmem_info.c Muchun Song
  2021-02-08  8:50 ` [PATCH v15 2/8] mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
@ 2021-02-08  8:50 ` Muchun Song
  2021-02-08  8:50 ` [PATCH v15 4/8] mm: hugetlb: alloc " Muchun Song
                   ` (4 subsequent siblings)
  7 siblings, 0 replies; 37+ messages in thread
From: Muchun Song @ 2021-02-08  8:50 UTC (permalink / raw)
  To: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, mchehab+huawei,
	pawan.kumar.gupta, rdunlap, oneukum, anshuman.khandual, jroedel,
	almasrymina, rientjes, willy, osalvador, mhocko, song.bao.hua,
	david, naoya.horiguchi, joao.m.martins
  Cc: duanxiongchun, linux-doc, linux-kernel, linux-mm, linux-fsdevel,
	Muchun Song

Every HugeTLB has more than one struct page structure. We __know__ that
we only use the first 4(HUGETLB_CGROUP_MIN_ORDER) 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>
---
 include/linux/bootmem_info.h |  27 +++++-
 include/linux/mm.h           |   3 +
 mm/Makefile                  |   1 +
 mm/hugetlb.c                 |   3 +
 mm/hugetlb_vmemmap.c         | 219 +++++++++++++++++++++++++++++++++++++++++++
 mm/hugetlb_vmemmap.h         |  20 ++++
 mm/sparse-vmemmap.c          | 207 ++++++++++++++++++++++++++++++++++++++++
 7 files changed, 479 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..ec03a624dfa2 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 +56,10 @@ static inline void get_page_bootmem(unsigned long info, struct page *page,
 				    unsigned long type)
 {
 }
+
+static inline void free_bootmem_page(struct page *page)
+{
+}
 #endif
 
 #endif /* __LINUX_BOOTMEM_INFO_H */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a608feb0d42e..d7dddf334779 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2979,6 +2979,9 @@ 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 ce4ddbe4461d..47b250e4c9b2 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -71,6 +71,7 @@ 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 8c53f3f2e12e..4cfca27c6d32 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -42,6 +42,7 @@
 #include <linux/userfaultfd_k.h>
 #include <linux/page_owner.h>
 #include "internal.h"
+#include "hugetlb_vmemmap.h"
 
 int hugetlb_max_hstate __read_mostly;
 unsigned int default_hstate_idx;
@@ -1462,6 +1463,8 @@ 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);
 	set_hugetlb_cgroup(page, NULL);
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
new file mode 100644
index 000000000000..0209b736e0b4
--- /dev/null
+++ b/mm/hugetlb_vmemmap.c
@@ -0,0 +1,219 @@
+// 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. 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 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..d3076a7a3783 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -27,8 +27,215 @@
 #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 = 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) {
+		BUG_ON(pte_none(*pte));
+		BUG_ON(walk->reuse_addr != addr);
+
+		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;
+	}
+
+	for (; addr != end; addr += PAGE_SIZE, pte++) {
+		BUG_ON(pte_none(*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_none(*pmd) || 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 {
+		BUG_ON(pud_none(*pud));
+
+		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 {
+		BUG_ON(p4d_none(*p4d));
+
+		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 {
+		BUG_ON(pgd_none(*pgd));
+
+		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 related	[flat|nested] 37+ messages in thread

* [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-08  8:50 [PATCH v15 0/8] Free some vmemmap pages of HugeTLB page Muchun Song
                   ` (2 preceding siblings ...)
  2021-02-08  8:50 ` [PATCH v15 3/8] mm: hugetlb: free the vmemmap pages associated with each HugeTLB page Muchun Song
@ 2021-02-08  8:50 ` Muchun Song
  2021-02-11 18:05   ` Mike Kravetz
  2021-02-12 15:32   ` Michal Hocko
  2021-02-08  8:50 ` [PATCH v15 5/8] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap Muchun Song
                   ` (3 subsequent siblings)
  7 siblings, 2 replies; 37+ messages in thread
From: Muchun Song @ 2021-02-08  8:50 UTC (permalink / raw)
  To: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, mchehab+huawei,
	pawan.kumar.gupta, rdunlap, oneukum, anshuman.khandual, jroedel,
	almasrymina, rientjes, willy, osalvador, mhocko, song.bao.hua,
	david, naoya.horiguchi, joao.m.martins
  Cc: duanxiongchun, linux-doc, linux-kernel, linux-mm, linux-fsdevel,
	Muchun Song

When we free a HugeTLB page to the buddy allocator, we should allocate the
vmemmap pages associated with it. But we may cannot allocate vmemmap pages
when the system is under memory pressure, in this case, we just refuse to
free the HugeTLB page instead of looping forever trying to allocate the
pages.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 include/linux/mm.h   |  2 ++
 mm/hugetlb.c         | 19 ++++++++++++-
 mm/hugetlb_vmemmap.c | 30 +++++++++++++++++++++
 mm/hugetlb_vmemmap.h |  6 +++++
 mm/sparse-vmemmap.c  | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 5 files changed, 130 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index d7dddf334779..33c5911afe18 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2981,6 +2981,8 @@ 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 4cfca27c6d32..69dcbaa2e6db 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1397,16 +1397,26 @@ static void __free_huge_page(struct page *page)
 		h->resv_huge_pages++;
 
 	if (HPageTemporary(page)) {
-		list_del(&page->lru);
 		ClearHPageTemporary(page);
+
+		if (alloc_huge_page_vmemmap(h, page)) {
+			h->surplus_huge_pages++;
+			h->surplus_huge_pages_node[nid]++;
+			goto enqueue;
+		}
+		list_del(&page->lru);
 		update_and_free_page(h, page);
 	} else if (h->surplus_huge_pages_node[nid]) {
+		if (alloc_huge_page_vmemmap(h, page))
+			goto enqueue;
+
 		/* remove the page from active list */
 		list_del(&page->lru);
 		update_and_free_page(h, page);
 		h->surplus_huge_pages--;
 		h->surplus_huge_pages_node[nid]--;
 	} else {
+enqueue:
 		arch_clear_hugepage_flags(page);
 		enqueue_huge_page(h, page);
 	}
@@ -1693,6 +1703,10 @@ static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
 			struct page *page =
 				list_entry(h->hugepage_freelists[node].next,
 					  struct page, lru);
+
+			if (alloc_huge_page_vmemmap(h, page))
+				break;
+
 			list_del(&page->lru);
 			h->free_huge_pages--;
 			h->free_huge_pages_node[node]--;
@@ -1760,6 +1774,9 @@ int dissolve_free_huge_page(struct page *page)
 			goto retry;
 		}
 
+		if (alloc_huge_page_vmemmap(h, head))
+			goto out;
+
 		/*
 		 * Move PageHWPoison flag from head page to the raw error page,
 		 * which makes any subpages rather than the error page reusable.
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 0209b736e0b4..3d85e3ab7caa 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -169,6 +169,8 @@
  * (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"
 
 /*
@@ -198,6 +200,34 @@ static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
 	return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
 }
 
+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 (!free_vmemmap_pages_per_hpage(h))
+		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_ATOMIC | __GFP_NOWARN | __GFP_THISNODE);
+	if (ret == -ENOMEM)
+		pr_info("cannot alloc vmemmap pages\n");
+
+	return ret;
+}
+
 void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 {
 	unsigned long vmemmap_addr = (unsigned long)head;
diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
index 6923f03534d5..e5547d53b9f5 100644
--- a/mm/hugetlb_vmemmap.h
+++ b/mm/hugetlb_vmemmap.h
@@ -11,8 +11,14 @@
 #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);
 #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 d3076a7a3783..60fc6cd6cd23 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,
@@ -237,6 +238,78 @@ 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 related	[flat|nested] 37+ messages in thread

* [PATCH v15 5/8] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap
  2021-02-08  8:50 [PATCH v15 0/8] Free some vmemmap pages of HugeTLB page Muchun Song
                   ` (3 preceding siblings ...)
  2021-02-08  8:50 ` [PATCH v15 4/8] mm: hugetlb: alloc " Muchun Song
@ 2021-02-08  8:50 ` Muchun Song
  2021-02-08  8:50 ` [PATCH v15 6/8] mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate Muchun Song
                   ` (2 subsequent siblings)
  7 siblings, 0 replies; 37+ messages in thread
From: Muchun Song @ 2021-02-08  8:50 UTC (permalink / raw)
  To: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, mchehab+huawei,
	pawan.kumar.gupta, rdunlap, oneukum, anshuman.khandual, jroedel,
	almasrymina, rientjes, willy, osalvador, mhocko, song.bao.hua,
	david, naoya.horiguchi, joao.m.martins
  Cc: duanxiongchun, linux-doc, linux-kernel, linux-mm, linux-fsdevel,
	Muchun Song, Miaohe Lin

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>
---
 Documentation/admin-guide/kernel-parameters.txt | 14 ++++++++++++++
 Documentation/admin-guide/mm/hugetlbpage.rst    |  3 +++
 arch/x86/mm/init_64.c                           |  8 ++++++--
 include/linux/hugetlb.h                         | 19 +++++++++++++++++++
 mm/hugetlb_vmemmap.c                            | 22 ++++++++++++++++++++++
 5 files changed, 64 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 5adf1e57e932..7db2591f3ad3 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1577,6 +1577,20 @@
 			Documentation/admin-guide/mm/hugetlbpage.rst.
 			Format: size[KMG]
 
+	hugetlb_free_vmemmap=
+			[KNL] When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set,
+			this controls freeing unused vmemmap pages associated
+			with each HugeTLB page. When this option is enabled,
+			we disable PMD/huge page mapping of vmemmap pages which
+			increase page table pages. So if a user/sysadmin only
+			uses a small number of HugeTLB pages (as a percentage
+			of system memory), they could end up using more memory
+			with hugetlb_free_vmemmap on as opposed to off.
+			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 f7b1c7462991..3a23c2377acc 100644
--- a/Documentation/admin-guide/mm/hugetlbpage.rst
+++ b/Documentation/admin-guide/mm/hugetlbpage.rst
@@ -145,6 +145,9 @@ 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 0435bee2e172..39f88c5faadc 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>
@@ -1557,7 +1558,8 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 {
 	int err;
 
-	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);
@@ -1585,6 +1587,8 @@ 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;
@@ -1610,7 +1614,7 @@ 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 37fd248ce271..ad249e56ac49 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -854,6 +854,20 @@ static inline void huge_ptep_modify_prot_commit(struct vm_area_struct *vma,
 
 void set_page_huge_active(struct page *page);
 
+#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 {};
 
@@ -1007,6 +1021,11 @@ 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 3d85e3ab7caa..2fa6fff9f5dd 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -183,6 +183,28 @@
 #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);
+
 /*
  * How many vmemmap pages associated with a HugeTLB page that can be freed
  * to the buddy allocator.
-- 
2.11.0



^ permalink raw reply related	[flat|nested] 37+ messages in thread

* [PATCH v15 6/8] mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate
  2021-02-08  8:50 [PATCH v15 0/8] Free some vmemmap pages of HugeTLB page Muchun Song
                   ` (4 preceding siblings ...)
  2021-02-08  8:50 ` [PATCH v15 5/8] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap Muchun Song
@ 2021-02-08  8:50 ` Muchun Song
  2021-02-08  8:50 ` [PATCH v15 7/8] mm: hugetlb: gather discrete indexes of tail page Muchun Song
  2021-02-08  8:50 ` [PATCH v15 8/8] mm: hugetlb: optimize the code with the help of the compiler Muchun Song
  7 siblings, 0 replies; 37+ messages in thread
From: Muchun Song @ 2021-02-08  8:50 UTC (permalink / raw)
  To: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, mchehab+huawei,
	pawan.kumar.gupta, rdunlap, oneukum, anshuman.khandual, jroedel,
	almasrymina, rientjes, willy, osalvador, mhocko, song.bao.hua,
	david, naoya.horiguchi, joao.m.martins
  Cc: duanxiongchun, linux-doc, linux-kernel, linux-mm, linux-fsdevel,
	Muchun Song, Miaohe Lin

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.

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>
---
 include/linux/hugetlb.h |  3 +++
 mm/hugetlb.c            |  1 +
 mm/hugetlb_vmemmap.c    | 30 ++++++++++++++++++++++++++----
 mm/hugetlb_vmemmap.h    |  5 +++++
 4 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index ad249e56ac49..775aea53669a 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -560,6 +560,9 @@ 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 69dcbaa2e6db..89b500075d1f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3220,6 +3220,7 @@ 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 2fa6fff9f5dd..ac29753fb297 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -208,13 +208,10 @@ early_param("hugetlb_free_vmemmap", early_hugetlb_free_vmemmap_param);
 /*
  * 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;
 }
 
 static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
@@ -269,3 +266,28 @@ void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 	 */
 	vmemmap_remap_free(vmemmap_addr, vmemmap_end, vmemmap_reuse);
 }
+
+void __init hugetlb_vmemmap_init(struct hstate *h)
+{
+	unsigned int nr_pages = pages_per_huge_page(h);
+	unsigned int vmemmap_pages;
+
+	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 e5547d53b9f5..9bc35d328ddf 100644
--- a/mm/hugetlb_vmemmap.h
+++ b/mm/hugetlb_vmemmap.h
@@ -13,6 +13,7 @@
 #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);
 #else
 static inline int alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
 {
@@ -22,5 +23,9 @@ static inline int alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
 static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 {
 }
+
+static inline void hugetlb_vmemmap_init(struct hstate *h)
+{
+}
 #endif /* CONFIG_HUGETLB_PAGE_FREE_VMEMMAP */
 #endif /* _LINUX_HUGETLB_VMEMMAP_H */
-- 
2.11.0



^ permalink raw reply related	[flat|nested] 37+ messages in thread

* [PATCH v15 7/8] mm: hugetlb: gather discrete indexes of tail page
  2021-02-08  8:50 [PATCH v15 0/8] Free some vmemmap pages of HugeTLB page Muchun Song
                   ` (5 preceding siblings ...)
  2021-02-08  8:50 ` [PATCH v15 6/8] mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate Muchun Song
@ 2021-02-08  8:50 ` Muchun Song
  2021-02-08  8:50 ` [PATCH v15 8/8] mm: hugetlb: optimize the code with the help of the compiler Muchun Song
  7 siblings, 0 replies; 37+ messages in thread
From: Muchun Song @ 2021-02-08  8:50 UTC (permalink / raw)
  To: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, mchehab+huawei,
	pawan.kumar.gupta, rdunlap, oneukum, anshuman.khandual, jroedel,
	almasrymina, rientjes, willy, osalvador, mhocko, song.bao.hua,
	david, naoya.horiguchi, joao.m.martins
  Cc: duanxiongchun, linux-doc, linux-kernel, linux-mm, linux-fsdevel,
	Muchun Song, Miaohe Lin

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.

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>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
---
 include/linux/hugetlb.h        | 20 ++++++++++++++++++--
 include/linux/hugetlb_cgroup.h | 19 +++++++++++--------
 mm/hugetlb_vmemmap.c           |  8 ++++++++
 3 files changed, 37 insertions(+), 10 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 775aea53669a..822ab2f5542a 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -28,6 +28,22 @@ 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 */
+#endif
+	NR_USED_SUBPAGE,
+};
+
 struct hugepage_subpool {
 	spinlock_t lock;
 	long count;
@@ -607,13 +623,13 @@ 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 2ad6e92f124a..c0cae6a704f2 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(NR_USED_SUBPAGE)
 
-#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;
 }
 
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index ac29753fb297..a67301a9d19a 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -272,6 +272,14 @@ 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;
 
-- 
2.11.0



^ permalink raw reply related	[flat|nested] 37+ messages in thread

* [PATCH v15 8/8] mm: hugetlb: optimize the code with the help of the compiler
  2021-02-08  8:50 [PATCH v15 0/8] Free some vmemmap pages of HugeTLB page Muchun Song
                   ` (6 preceding siblings ...)
  2021-02-08  8:50 ` [PATCH v15 7/8] mm: hugetlb: gather discrete indexes of tail page Muchun Song
@ 2021-02-08  8:50 ` Muchun Song
  7 siblings, 0 replies; 37+ messages in thread
From: Muchun Song @ 2021-02-08  8:50 UTC (permalink / raw)
  To: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, mchehab+huawei,
	pawan.kumar.gupta, rdunlap, oneukum, anshuman.khandual, jroedel,
	almasrymina, rientjes, willy, osalvador, mhocko, song.bao.hua,
	david, naoya.horiguchi, joao.m.martins
  Cc: duanxiongchun, linux-doc, linux-kernel, linux-mm, linux-fsdevel,
	Muchun Song, Miaohe Lin

When the "struct page size" crosses page boundaries we cannot
make use of this feature. Let free_vmemmap_pages_per_hpage()
return zero if that is the case, most of the functions can be
optimized away.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
---
 include/linux/hugetlb.h |  3 ++-
 mm/hugetlb_vmemmap.c    | 13 +++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 822ab2f5542a..7bfb06e16298 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -878,7 +878,8 @@ extern bool hugetlb_free_vmemmap_enabled;
 
 static inline bool is_hugetlb_free_vmemmap_enabled(void)
 {
-	return hugetlb_free_vmemmap_enabled;
+	return hugetlb_free_vmemmap_enabled &&
+	       is_power_of_2(sizeof(struct page));
 }
 #else
 static inline bool is_hugetlb_free_vmemmap_enabled(void)
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index a67301a9d19a..2e7e1d6ee458 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -211,6 +211,12 @@ early_param("hugetlb_free_vmemmap", early_hugetlb_free_vmemmap_param);
  */
 static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
 {
+	/*
+	 * This check aims to let the compiler help us optimize the code as
+	 * much as possible.
+	 */
+	if (!is_power_of_2(sizeof(struct page)))
+		return 0;
 	return h->nr_free_vmemmap_pages;
 }
 
@@ -280,6 +286,13 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
 	BUILD_BUG_ON(NR_USED_SUBPAGE >=
 		     RESERVE_VMEMMAP_SIZE / sizeof(struct page));
 
+	/*
+	 * The compiler can help us to optimize this function to null
+	 * when the size of the struct page is not power of 2.
+	 */
+	if (!is_power_of_2(sizeof(struct page)))
+		return;
+
 	if (!hugetlb_free_vmemmap_enabled)
 		return;
 
-- 
2.11.0



^ permalink raw reply related	[flat|nested] 37+ messages in thread

* Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-08  8:50 ` [PATCH v15 4/8] mm: hugetlb: alloc " Muchun Song
@ 2021-02-11 18:05   ` Mike Kravetz
  2021-02-12 14:15     ` David Hildenbrand
  2021-02-12 15:32   ` Michal Hocko
  1 sibling, 1 reply; 37+ messages in thread
From: Mike Kravetz @ 2021-02-11 18:05 UTC (permalink / raw)
  To: Muchun Song, corbet, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, mchehab+huawei,
	pawan.kumar.gupta, rdunlap, oneukum, anshuman.khandual, jroedel,
	almasrymina, rientjes, willy, osalvador, mhocko, song.bao.hua,
	david, naoya.horiguchi, joao.m.martins
  Cc: duanxiongchun, linux-doc, linux-kernel, linux-mm, linux-fsdevel

On 2/8/21 12:50 AM, Muchun Song wrote:
> When we free a HugeTLB page to the buddy allocator, we should allocate the
> vmemmap pages associated with it. But we may cannot allocate vmemmap pages
> when the system is under memory pressure, in this case, we just refuse to
> free the HugeTLB page instead of looping forever trying to allocate the
> pages.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  include/linux/mm.h   |  2 ++
>  mm/hugetlb.c         | 19 ++++++++++++-
>  mm/hugetlb_vmemmap.c | 30 +++++++++++++++++++++
>  mm/hugetlb_vmemmap.h |  6 +++++
>  mm/sparse-vmemmap.c  | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++-
>  5 files changed, 130 insertions(+), 2 deletions(-)

Muchun has done a great job simplifying this patch series and addressing
issues as they are brought up.  This patch addresses the issue which seems
to be the biggest stumbling block to this series.  The need to allocate
vmemmap pages to dissolve a hugetlb page to the buddy allocator.  The way
it is addressed in this patch is to simply fail to dissolve the hugetlb
page if the vmmemmap pages can not be allocated.  IMO, this is an 'acceptable'
strategy.  If we find ourselves in this situation then we are likely to be
hitting other corner cases in the system.  I wish there was a perfect way
to address this issue, but we have been unable to come up with one.

There was a decent discussion about this is a previous version of the
series starting here:
https://lore.kernel.org/linux-mm/20210126092942.GA10602@linux/
In this thread various other options were suggested and discussed.

I would like to come to some agreement on an acceptable way to handle this
specific issue.  IMO, it makes little sense to continue refining other
parts of this series if we can not figure out how to move forward on this
issue.

It would be great if David H, David R and Michal could share their opinions
on this.  No need to review details the code yet (unless you want), but
let's start a discussion on how to move past this issue if we can.
-- 
Mike Kravetz


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-11 18:05   ` Mike Kravetz
@ 2021-02-12 14:15     ` David Hildenbrand
  0 siblings, 0 replies; 37+ messages in thread
From: David Hildenbrand @ 2021-02-12 14:15 UTC (permalink / raw)
  To: Mike Kravetz, Muchun Song, corbet, tglx, mingo, bp, x86, hpa,
	dave.hansen, luto, peterz, viro, akpm, paulmck, mchehab+huawei,
	pawan.kumar.gupta, rdunlap, oneukum, anshuman.khandual, jroedel,
	almasrymina, rientjes, willy, osalvador, mhocko, song.bao.hua,
	naoya.horiguchi, joao.m.martins
  Cc: duanxiongchun, linux-doc, linux-kernel, linux-mm, linux-fsdevel

On 11.02.21 19:05, Mike Kravetz wrote:
> On 2/8/21 12:50 AM, Muchun Song wrote:
>> When we free a HugeTLB page to the buddy allocator, we should allocate the
>> vmemmap pages associated with it. But we may cannot allocate vmemmap pages
>> when the system is under memory pressure, in this case, we just refuse to
>> free the HugeTLB page instead of looping forever trying to allocate the
>> pages.
>>
>> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
>> ---
>>   include/linux/mm.h   |  2 ++
>>   mm/hugetlb.c         | 19 ++++++++++++-
>>   mm/hugetlb_vmemmap.c | 30 +++++++++++++++++++++
>>   mm/hugetlb_vmemmap.h |  6 +++++
>>   mm/sparse-vmemmap.c  | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++-
>>   5 files changed, 130 insertions(+), 2 deletions(-)
> 
> Muchun has done a great job simplifying this patch series and addressing
> issues as they are brought up.  This patch addresses the issue which seems
> to be the biggest stumbling block to this series.  The need to allocate
> vmemmap pages to dissolve a hugetlb page to the buddy allocator.  The way
> it is addressed in this patch is to simply fail to dissolve the hugetlb
> page if the vmmemmap pages can not be allocated.  IMO, this is an 'acceptable'
> strategy.  If we find ourselves in this situation then we are likely to be
> hitting other corner cases in the system.  I wish there was a perfect way
> to address this issue, but we have been unable to come up with one.
> 
> There was a decent discussion about this is a previous version of the
> series starting here:
> https://lore.kernel.org/linux-mm/20210126092942.GA10602@linux/
> In this thread various other options were suggested and discussed.
> 
> I would like to come to some agreement on an acceptable way to handle this
> specific issue.  IMO, it makes little sense to continue refining other
> parts of this series if we can not figure out how to move forward on this
> issue.
> 
> It would be great if David H, David R and Michal could share their opinions
> on this.  No need to review details the code yet (unless you want), but
> let's start a discussion on how to move past this issue if we can.

So a summary from my side:

We might fail freeing a huge page at any point in time iff we are low on 
kernel (!CMA, !ZONE_MOVABLE) memory. While we could play games with 
allocating the vmemmap from a huge page itself in some cases (e.g., 
!CMA, !ZONE_MOVABLE), simply retrying is way easier and we don't turn 
the huge page forever unusable.

Corner cases might be having many huge pages in ZONE_MOVABLE, freeing 
them all at once and eating up a lot of kernel memory. But then, the 
same setup would already be problematic nowadays where we simply always 
consume that kernel memory for the vmemmap.

I think this problem only really becomes visible in corner cases. And 
someone actively has to enable new behavior.


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

Bad luck. Try again later.

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

Bad luck. But who will try again later?

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

This is a bit unfortunate if we have plenty of ZONE_MOVABLE memory but 
are low on kernel memory. For example, migration of huge pages would 
still work, however, dissolving the free page does not work. I'd say 
this is a corner cases. When the system is that much under memory 
pressure, offlining/unplug can be expected to fail.

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. However, we didn't even take care of huge pages *at all* 
for now (neither migrate nor dissolve). So actually don't make the 
current state any worse. virito-mem will handle migration errors 
gracefully. CMA might be able to fallback on other free areas within the 
CMA region.


I'd say, document the changed behavior properly so people are aware that 
there might be issues in corner cases with huge pages on CMA / ZONE_MOVABLE.

-- 
Thanks,

David / dhildenb



^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-08  8:50 ` [PATCH v15 4/8] mm: hugetlb: alloc " Muchun Song
  2021-02-11 18:05   ` Mike Kravetz
@ 2021-02-12 15:32   ` Michal Hocko
  2021-02-15 10:05     ` [External] " Muchun Song
  1 sibling, 1 reply; 37+ messages in thread
From: Michal Hocko @ 2021-02-12 15:32 UTC (permalink / raw)
  To: Muchun Song
  Cc: corbet, mike.kravetz, tglx, mingo, bp, x86, hpa, dave.hansen,
	luto, peterz, viro, akpm, paulmck, mchehab+huawei,
	pawan.kumar.gupta, rdunlap, oneukum, anshuman.khandual, jroedel,
	almasrymina, rientjes, willy, osalvador, song.bao.hua, david,
	naoya.horiguchi, joao.m.martins, duanxiongchun, linux-doc,
	linux-kernel, linux-mm, linux-fsdevel

On Mon 08-02-21 16:50:09, Muchun Song wrote:
> When we free a HugeTLB page to the buddy allocator, we should allocate the
> vmemmap pages associated with it. But we may cannot allocate vmemmap pages
> when the system is under memory pressure, in this case, we just refuse to
> free the HugeTLB page instead of looping forever trying to allocate the
> pages.

Thanks for simplifying the implementation from your early proposal!

This will not be looping for ever. The allocation will usually trigger
the OOM killer and sooner or later there will be a memory to allocate
from or the system panics when there are no eligible tasks to kill. This
is just a side note.

I think the changelog could benefit from a more explicit documentation
of those error failures. There are different cases when the hugetlb page
is freed. It can be due to an admin intervention (decrease the pool),
overcommit, migration, dissolving and likely some others. Most of them
should be fine to stay in the pool which would just increase the surplus
pages in the pool. I am not so sure about dissolving path.
[...]
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index 0209b736e0b4..3d85e3ab7caa 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -169,6 +169,8 @@
>   * (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"
>  
>  /*
> @@ -198,6 +200,34 @@ static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
>  	return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
>  }
>  
> +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 (!free_vmemmap_pages_per_hpage(h))
> +		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_ATOMIC | __GFP_NOWARN | __GFP_THISNODE);

I do not think that this is a good allocation mode. GFP_ATOMIC is a non
sleeping allocation and a medium memory pressure might cause it to
fail prematurely. I do not think this is really an atomic context which
couldn't afford memory reclaim. I also do not think we want to grant
access to memory reserve is reasonable. Just think of a huge number of
hugetlb pages being freed which can deplete the memory reserve for
atomic allocations. I think that you want 
	GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN | __GFP_THISNODE

for an initial implementation. The justification being that the
allocation should at least try to reclaim but it shouldn't cause any
major disruption because the failure is not fatal. If the failure rate
would be impractically high then just drop NORETRY part. You can replace
it by __GFP_RETRY_MAYFAIL but that shouldn't be strictly necessary
because __GFP_THISNODE on its own implies on OOM killer, but that is
kinda ugly to rely on.
-- 
Michal Hocko
SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-12 15:32   ` Michal Hocko
@ 2021-02-15 10:05     ` Muchun Song
  2021-02-15 10:33       ` Michal Hocko
  0 siblings, 1 reply; 37+ messages in thread
From: Muchun Song @ 2021-02-15 10:05 UTC (permalink / raw)
  To: Michal Hocko
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Fri, Feb 12, 2021 at 11:32 PM Michal Hocko <mhocko@suse.com> wrote:
>
> On Mon 08-02-21 16:50:09, Muchun Song wrote:
> > When we free a HugeTLB page to the buddy allocator, we should allocate the
> > vmemmap pages associated with it. But we may cannot allocate vmemmap pages
> > when the system is under memory pressure, in this case, we just refuse to
> > free the HugeTLB page instead of looping forever trying to allocate the
> > pages.
>
> Thanks for simplifying the implementation from your early proposal!
>
> This will not be looping for ever. The allocation will usually trigger
> the OOM killer and sooner or later there will be a memory to allocate
> from or the system panics when there are no eligible tasks to kill. This
> is just a side note.
>
> I think the changelog could benefit from a more explicit documentation
> of those error failures. There are different cases when the hugetlb page
> is freed. It can be due to an admin intervention (decrease the pool),
> overcommit, migration, dissolving and likely some others. Most of them
> should be fine to stay in the pool which would just increase the surplus
> pages in the pool. I am not so sure about dissolving path.

Thanks. I will update the changelog.

> [...]
> > diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> > index 0209b736e0b4..3d85e3ab7caa 100644
> > --- a/mm/hugetlb_vmemmap.c
> > +++ b/mm/hugetlb_vmemmap.c
> > @@ -169,6 +169,8 @@
> >   * (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"
> >
> >  /*
> > @@ -198,6 +200,34 @@ static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
> >       return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
> >  }
> >
> > +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 (!free_vmemmap_pages_per_hpage(h))
> > +             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_ATOMIC | __GFP_NOWARN | __GFP_THISNODE);
>
> I do not think that this is a good allocation mode. GFP_ATOMIC is a non
> sleeping allocation and a medium memory pressure might cause it to
> fail prematurely. I do not think this is really an atomic context which
> couldn't afford memory reclaim. I also do not think we want to grant

Because alloc_huge_page_vmemmap is called under hugetlb_lock
now. So using GFP_ATOMIC indeed makes the code more simpler.
From the document of the kernel, I learned that __GFP_NOMEMALLOC
can be used to explicitly forbid access to emergency reserves. So if
we do not want to use the reserve memory. How about replacing it to

GFP_ATOMIC | __GFP_NOMEMALLOC | __GFP_NOWARN | __GFP_THISNODE

Thanks.

> access to memory reserve is reasonable. Just think of a huge number of
> hugetlb pages being freed which can deplete the memory reserve for
> atomic allocations. I think that you want
>         GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN | __GFP_THISNODE
>
> for an initial implementation. The justification being that the
> allocation should at least try to reclaim but it shouldn't cause any
> major disruption because the failure is not fatal. If the failure rate
> would be impractically high then just drop NORETRY part. You can replace
> it by __GFP_RETRY_MAYFAIL but that shouldn't be strictly necessary
> because __GFP_THISNODE on its own implies on OOM killer, but that is
> kinda ugly to rely on.
> --
> Michal Hocko
> SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-15 10:05     ` [External] " Muchun Song
@ 2021-02-15 10:33       ` Michal Hocko
  2021-02-15 11:51         ` Muchun Song
  0 siblings, 1 reply; 37+ messages in thread
From: Michal Hocko @ 2021-02-15 10:33 UTC (permalink / raw)
  To: Muchun Song
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Mon 15-02-21 18:05:06, Muchun Song wrote:
> On Fri, Feb 12, 2021 at 11:32 PM Michal Hocko <mhocko@suse.com> wrote:
[...]
> > > +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 (!free_vmemmap_pages_per_hpage(h))
> > > +             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_ATOMIC | __GFP_NOWARN | __GFP_THISNODE);
> >
> > I do not think that this is a good allocation mode. GFP_ATOMIC is a non
> > sleeping allocation and a medium memory pressure might cause it to
> > fail prematurely. I do not think this is really an atomic context which
> > couldn't afford memory reclaim. I also do not think we want to grant
> 
> Because alloc_huge_page_vmemmap is called under hugetlb_lock
> now. So using GFP_ATOMIC indeed makes the code more simpler.

You can have a preallocated list of pages prior taking the lock.
Moreover do we want to manipulate vmemmaps from under spinlock in
general. I have to say I have missed that detail when reviewing. Need to
think more.

> From the document of the kernel, I learned that __GFP_NOMEMALLOC
> can be used to explicitly forbid access to emergency reserves. So if
> we do not want to use the reserve memory. How about replacing it to
> 
> GFP_ATOMIC | __GFP_NOMEMALLOC | __GFP_NOWARN | __GFP_THISNODE

The whole point of GFP_ATOMIC is to grant access to memory reserves so
the above is quite dubious. If you do not want access to memory reserves
then use GFP_NOWAIT instead. But failures are much more easier to happen
then.

NOMEMALLOC is meant to be used from paths which are allowed to consume
memory reserves - e.g. when invoked from the memory reclaim path.
-- 
Michal Hocko
SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-15 10:33       ` Michal Hocko
@ 2021-02-15 11:51         ` Muchun Song
  2021-02-15 12:00           ` Muchun Song
  2021-02-15 12:24           ` Michal Hocko
  0 siblings, 2 replies; 37+ messages in thread
From: Muchun Song @ 2021-02-15 11:51 UTC (permalink / raw)
  To: Michal Hocko
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Mon, Feb 15, 2021 at 6:33 PM Michal Hocko <mhocko@suse.com> wrote:
>
> On Mon 15-02-21 18:05:06, Muchun Song wrote:
> > On Fri, Feb 12, 2021 at 11:32 PM Michal Hocko <mhocko@suse.com> wrote:
> [...]
> > > > +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 (!free_vmemmap_pages_per_hpage(h))
> > > > +             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_ATOMIC | __GFP_NOWARN | __GFP_THISNODE);
> > >
> > > I do not think that this is a good allocation mode. GFP_ATOMIC is a non
> > > sleeping allocation and a medium memory pressure might cause it to
> > > fail prematurely. I do not think this is really an atomic context which
> > > couldn't afford memory reclaim. I also do not think we want to grant
> >
> > Because alloc_huge_page_vmemmap is called under hugetlb_lock
> > now. So using GFP_ATOMIC indeed makes the code more simpler.
>
> You can have a preallocated list of pages prior taking the lock.

A discussion about this can refer to here:

https://patchwork.kernel.org/project/linux-mm/patch/20210117151053.24600-5-songmuchun@bytedance.com/

> Moreover do we want to manipulate vmemmaps from under spinlock in
> general. I have to say I have missed that detail when reviewing. Need to
> think more.
>
> > From the document of the kernel, I learned that __GFP_NOMEMALLOC
> > can be used to explicitly forbid access to emergency reserves. So if
> > we do not want to use the reserve memory. How about replacing it to
> >
> > GFP_ATOMIC | __GFP_NOMEMALLOC | __GFP_NOWARN | __GFP_THISNODE
>
> The whole point of GFP_ATOMIC is to grant access to memory reserves so
> the above is quite dubious. If you do not want access to memory reserves

Look at the code of gfp_to_alloc_flags().

static inline unsigned int gfp_to_alloc_flags(gfp_t gfp_mask)
{
        [...]
        if (gfp_mask & __GFP_ATOMIC) {
        /*
         * Not worth trying to allocate harder for __GFP_NOMEMALLOC even
         * if it can't schedule.
         */
        if (!(gfp_mask & __GFP_NOMEMALLOC))
                alloc_flags |= ALLOC_HARDER;
       [...]
}

Seems to allow this operation (GFP_ATOMIC | __GFP_NOMEMALLOC).

> then use GFP_NOWAIT instead. But failures are much more easier to happen
> then.
>
> NOMEMALLOC is meant to be used from paths which are allowed to consume
> memory reserves - e.g. when invoked from the memory reclaim path.
> --
> Michal Hocko
> SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-15 11:51         ` Muchun Song
@ 2021-02-15 12:00           ` Muchun Song
  2021-02-15 12:18             ` Michal Hocko
  2021-02-15 12:24           ` Michal Hocko
  1 sibling, 1 reply; 37+ messages in thread
From: Muchun Song @ 2021-02-15 12:00 UTC (permalink / raw)
  To: Michal Hocko
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Mon, Feb 15, 2021 at 7:51 PM Muchun Song <songmuchun@bytedance.com> wrote:
>
> On Mon, Feb 15, 2021 at 6:33 PM Michal Hocko <mhocko@suse.com> wrote:
> >
> > On Mon 15-02-21 18:05:06, Muchun Song wrote:
> > > On Fri, Feb 12, 2021 at 11:32 PM Michal Hocko <mhocko@suse.com> wrote:
> > [...]
> > > > > +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 (!free_vmemmap_pages_per_hpage(h))
> > > > > +             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_ATOMIC | __GFP_NOWARN | __GFP_THISNODE);
> > > >
> > > > I do not think that this is a good allocation mode. GFP_ATOMIC is a non
> > > > sleeping allocation and a medium memory pressure might cause it to
> > > > fail prematurely. I do not think this is really an atomic context which
> > > > couldn't afford memory reclaim. I also do not think we want to grant
> > >
> > > Because alloc_huge_page_vmemmap is called under hugetlb_lock
> > > now. So using GFP_ATOMIC indeed makes the code more simpler.
> >
> > You can have a preallocated list of pages prior taking the lock.
>
> A discussion about this can refer to here:
>
> https://patchwork.kernel.org/project/linux-mm/patch/20210117151053.24600-5-songmuchun@bytedance.com/
>
> > Moreover do we want to manipulate vmemmaps from under spinlock in
> > general. I have to say I have missed that detail when reviewing. Need to
> > think more.
> >
> > > From the document of the kernel, I learned that __GFP_NOMEMALLOC
> > > can be used to explicitly forbid access to emergency reserves. So if
> > > we do not want to use the reserve memory. How about replacing it to
> > >
> > > GFP_ATOMIC | __GFP_NOMEMALLOC | __GFP_NOWARN | __GFP_THISNODE
> >
> > The whole point of GFP_ATOMIC is to grant access to memory reserves so
> > the above is quite dubious. If you do not want access to memory reserves
>
> Look at the code of gfp_to_alloc_flags().
>
> static inline unsigned int gfp_to_alloc_flags(gfp_t gfp_mask)
> {
>         [...]
>         if (gfp_mask & __GFP_ATOMIC) {
>         /*
>          * Not worth trying to allocate harder for __GFP_NOMEMALLOC even
>          * if it can't schedule.
>          */
>         if (!(gfp_mask & __GFP_NOMEMALLOC))
>                 alloc_flags |= ALLOC_HARDER;
>        [...]
> }
>
> Seems to allow this operation (GFP_ATOMIC | __GFP_NOMEMALLOC).

I also found similar users.

netdev_alloc_frag()
    page_frag_alloc(GFP_ATOMIC)
        __page_frag_cache_refill(GFP_ATOMIC)
            alloc_pages_node(GFP_ATOMIC | __GFP_COMP | __GFP_NOWARN |
__GFP_NORETRY |
                                                __GFP_NOMEMALLOC)

>
> > then use GFP_NOWAIT instead. But failures are much more easier to happen
> > then.
> >
> > NOMEMALLOC is meant to be used from paths which are allowed to consume
> > memory reserves - e.g. when invoked from the memory reclaim path.
> > --
> > Michal Hocko
> > SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-15 12:00           ` Muchun Song
@ 2021-02-15 12:18             ` Michal Hocko
  2021-02-15 12:44               ` Muchun Song
  0 siblings, 1 reply; 37+ messages in thread
From: Michal Hocko @ 2021-02-15 12:18 UTC (permalink / raw)
  To: Muchun Song
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Mon 15-02-21 20:00:07, Muchun Song wrote:
> On Mon, Feb 15, 2021 at 7:51 PM Muchun Song <songmuchun@bytedance.com> wrote:
> >
> > On Mon, Feb 15, 2021 at 6:33 PM Michal Hocko <mhocko@suse.com> wrote:
> > >
> > > On Mon 15-02-21 18:05:06, Muchun Song wrote:
> > > > On Fri, Feb 12, 2021 at 11:32 PM Michal Hocko <mhocko@suse.com> wrote:
> > > [...]
> > > > > > +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 (!free_vmemmap_pages_per_hpage(h))
> > > > > > +             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_ATOMIC | __GFP_NOWARN | __GFP_THISNODE);
> > > > >
> > > > > I do not think that this is a good allocation mode. GFP_ATOMIC is a non
> > > > > sleeping allocation and a medium memory pressure might cause it to
> > > > > fail prematurely. I do not think this is really an atomic context which
> > > > > couldn't afford memory reclaim. I also do not think we want to grant
> > > >
> > > > Because alloc_huge_page_vmemmap is called under hugetlb_lock
> > > > now. So using GFP_ATOMIC indeed makes the code more simpler.
> > >
> > > You can have a preallocated list of pages prior taking the lock.
> >
> > A discussion about this can refer to here:
> >
> > https://patchwork.kernel.org/project/linux-mm/patch/20210117151053.24600-5-songmuchun@bytedance.com/
> >
> > > Moreover do we want to manipulate vmemmaps from under spinlock in
> > > general. I have to say I have missed that detail when reviewing. Need to
> > > think more.
> > >
> > > > From the document of the kernel, I learned that __GFP_NOMEMALLOC
> > > > can be used to explicitly forbid access to emergency reserves. So if
> > > > we do not want to use the reserve memory. How about replacing it to
> > > >
> > > > GFP_ATOMIC | __GFP_NOMEMALLOC | __GFP_NOWARN | __GFP_THISNODE
> > >
> > > The whole point of GFP_ATOMIC is to grant access to memory reserves so
> > > the above is quite dubious. If you do not want access to memory reserves
> >
> > Look at the code of gfp_to_alloc_flags().
> >
> > static inline unsigned int gfp_to_alloc_flags(gfp_t gfp_mask)
> > {
> >         [...]
> >         if (gfp_mask & __GFP_ATOMIC) {
> >         /*
> >          * Not worth trying to allocate harder for __GFP_NOMEMALLOC even
> >          * if it can't schedule.
> >          */
> >         if (!(gfp_mask & __GFP_NOMEMALLOC))
> >                 alloc_flags |= ALLOC_HARDER;
> >        [...]
> > }
> >
> > Seems to allow this operation (GFP_ATOMIC | __GFP_NOMEMALLOC).

Please read my response again more carefully. I am not claiming that
combination is not allowed. I have said it doesn't make any sense in
this context.

-- 
Michal Hocko
SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-15 11:51         ` Muchun Song
  2021-02-15 12:00           ` Muchun Song
@ 2021-02-15 12:24           ` Michal Hocko
  1 sibling, 0 replies; 37+ messages in thread
From: Michal Hocko @ 2021-02-15 12:24 UTC (permalink / raw)
  To: Muchun Song
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Mon 15-02-21 19:51:26, Muchun Song wrote:
> On Mon, Feb 15, 2021 at 6:33 PM Michal Hocko <mhocko@suse.com> wrote:
> >
> > On Mon 15-02-21 18:05:06, Muchun Song wrote:
> > > On Fri, Feb 12, 2021 at 11:32 PM Michal Hocko <mhocko@suse.com> wrote:
> > [...]
> > > > > +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 (!free_vmemmap_pages_per_hpage(h))
> > > > > +             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_ATOMIC | __GFP_NOWARN | __GFP_THISNODE);
> > > >
> > > > I do not think that this is a good allocation mode. GFP_ATOMIC is a non
> > > > sleeping allocation and a medium memory pressure might cause it to
> > > > fail prematurely. I do not think this is really an atomic context which
> > > > couldn't afford memory reclaim. I also do not think we want to grant
> > >
> > > Because alloc_huge_page_vmemmap is called under hugetlb_lock
> > > now. So using GFP_ATOMIC indeed makes the code more simpler.
> >
> > You can have a preallocated list of pages prior taking the lock.
> 
> A discussion about this can refer to here:
> 
> https://patchwork.kernel.org/project/linux-mm/patch/20210117151053.24600-5-songmuchun@bytedance.com/

I do not see any real response to the pre-allocation argument except
that put_page can be called from an atomic context. Which might be true
in general but it is not the case for hugetlb pages. hugetlb_lock would
have to be irq safe otherwise. Also the whole operation can be scheduled
to a kworker context for a stronger allocation context.

-- 
Michal Hocko
SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-15 12:18             ` Michal Hocko
@ 2021-02-15 12:44               ` Muchun Song
  2021-02-15 13:19                 ` Michal Hocko
  0 siblings, 1 reply; 37+ messages in thread
From: Muchun Song @ 2021-02-15 12:44 UTC (permalink / raw)
  To: Michal Hocko
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Mon, Feb 15, 2021 at 8:18 PM Michal Hocko <mhocko@suse.com> wrote:
>
> On Mon 15-02-21 20:00:07, Muchun Song wrote:
> > On Mon, Feb 15, 2021 at 7:51 PM Muchun Song <songmuchun@bytedance.com> wrote:
> > >
> > > On Mon, Feb 15, 2021 at 6:33 PM Michal Hocko <mhocko@suse.com> wrote:
> > > >
> > > > On Mon 15-02-21 18:05:06, Muchun Song wrote:
> > > > > On Fri, Feb 12, 2021 at 11:32 PM Michal Hocko <mhocko@suse.com> wrote:
> > > > [...]
> > > > > > > +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 (!free_vmemmap_pages_per_hpage(h))
> > > > > > > +             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_ATOMIC | __GFP_NOWARN | __GFP_THISNODE);
> > > > > >
> > > > > > I do not think that this is a good allocation mode. GFP_ATOMIC is a non
> > > > > > sleeping allocation and a medium memory pressure might cause it to
> > > > > > fail prematurely. I do not think this is really an atomic context which
> > > > > > couldn't afford memory reclaim. I also do not think we want to grant
> > > > >
> > > > > Because alloc_huge_page_vmemmap is called under hugetlb_lock
> > > > > now. So using GFP_ATOMIC indeed makes the code more simpler.
> > > >
> > > > You can have a preallocated list of pages prior taking the lock.
> > >
> > > A discussion about this can refer to here:
> > >
> > > https://patchwork.kernel.org/project/linux-mm/patch/20210117151053.24600-5-songmuchun@bytedance.com/
> > >
> > > > Moreover do we want to manipulate vmemmaps from under spinlock in
> > > > general. I have to say I have missed that detail when reviewing. Need to
> > > > think more.
> > > >
> > > > > From the document of the kernel, I learned that __GFP_NOMEMALLOC
> > > > > can be used to explicitly forbid access to emergency reserves. So if
> > > > > we do not want to use the reserve memory. How about replacing it to
> > > > >
> > > > > GFP_ATOMIC | __GFP_NOMEMALLOC | __GFP_NOWARN | __GFP_THISNODE
> > > >
> > > > The whole point of GFP_ATOMIC is to grant access to memory reserves so
> > > > the above is quite dubious. If you do not want access to memory reserves
> > >
> > > Look at the code of gfp_to_alloc_flags().
> > >
> > > static inline unsigned int gfp_to_alloc_flags(gfp_t gfp_mask)
> > > {
> > >         [...]
> > >         if (gfp_mask & __GFP_ATOMIC) {
> > >         /*
> > >          * Not worth trying to allocate harder for __GFP_NOMEMALLOC even
> > >          * if it can't schedule.
> > >          */
> > >         if (!(gfp_mask & __GFP_NOMEMALLOC))
> > >                 alloc_flags |= ALLOC_HARDER;
> > >        [...]
> > > }
> > >
> > > Seems to allow this operation (GFP_ATOMIC | __GFP_NOMEMALLOC).
>
> Please read my response again more carefully. I am not claiming that
> combination is not allowed. I have said it doesn't make any sense in
> this context.

I see you are worried that using GFP_ATOMIC will use reverse memory
unlimited. So I think that __GFP_NOMEMALLOC may be suitable for us.
Sorry, I may not understand the point you said. What I missed?

>
> --
> Michal Hocko
> SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-15 12:44               ` Muchun Song
@ 2021-02-15 13:19                 ` Michal Hocko
  2021-02-15 15:36                   ` Muchun Song
  0 siblings, 1 reply; 37+ messages in thread
From: Michal Hocko @ 2021-02-15 13:19 UTC (permalink / raw)
  To: Muchun Song
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Mon 15-02-21 20:44:57, Muchun Song wrote:
> On Mon, Feb 15, 2021 at 8:18 PM Michal Hocko <mhocko@suse.com> wrote:
> >
> > On Mon 15-02-21 20:00:07, Muchun Song wrote:
> > > On Mon, Feb 15, 2021 at 7:51 PM Muchun Song <songmuchun@bytedance.com> wrote:
> > > >
> > > > On Mon, Feb 15, 2021 at 6:33 PM Michal Hocko <mhocko@suse.com> wrote:
> > > > >
> > > > > On Mon 15-02-21 18:05:06, Muchun Song wrote:
> > > > > > On Fri, Feb 12, 2021 at 11:32 PM Michal Hocko <mhocko@suse.com> wrote:
> > > > > [...]
> > > > > > > > +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 (!free_vmemmap_pages_per_hpage(h))
> > > > > > > > +             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_ATOMIC | __GFP_NOWARN | __GFP_THISNODE);
> > > > > > >
> > > > > > > I do not think that this is a good allocation mode. GFP_ATOMIC is a non
> > > > > > > sleeping allocation and a medium memory pressure might cause it to
> > > > > > > fail prematurely. I do not think this is really an atomic context which
> > > > > > > couldn't afford memory reclaim. I also do not think we want to grant
> > > > > >
> > > > > > Because alloc_huge_page_vmemmap is called under hugetlb_lock
> > > > > > now. So using GFP_ATOMIC indeed makes the code more simpler.
> > > > >
> > > > > You can have a preallocated list of pages prior taking the lock.
> > > >
> > > > A discussion about this can refer to here:
> > > >
> > > > https://patchwork.kernel.org/project/linux-mm/patch/20210117151053.24600-5-songmuchun@bytedance.com/
> > > >
> > > > > Moreover do we want to manipulate vmemmaps from under spinlock in
> > > > > general. I have to say I have missed that detail when reviewing. Need to
> > > > > think more.
> > > > >
> > > > > > From the document of the kernel, I learned that __GFP_NOMEMALLOC
> > > > > > can be used to explicitly forbid access to emergency reserves. So if
> > > > > > we do not want to use the reserve memory. How about replacing it to
> > > > > >
> > > > > > GFP_ATOMIC | __GFP_NOMEMALLOC | __GFP_NOWARN | __GFP_THISNODE
> > > > >
> > > > > The whole point of GFP_ATOMIC is to grant access to memory reserves so
> > > > > the above is quite dubious. If you do not want access to memory reserves
> > > >
> > > > Look at the code of gfp_to_alloc_flags().
> > > >
> > > > static inline unsigned int gfp_to_alloc_flags(gfp_t gfp_mask)
> > > > {
> > > >         [...]
> > > >         if (gfp_mask & __GFP_ATOMIC) {
> > > >         /*
> > > >          * Not worth trying to allocate harder for __GFP_NOMEMALLOC even
> > > >          * if it can't schedule.
> > > >          */
> > > >         if (!(gfp_mask & __GFP_NOMEMALLOC))
> > > >                 alloc_flags |= ALLOC_HARDER;
> > > >        [...]
> > > > }
> > > >
> > > > Seems to allow this operation (GFP_ATOMIC | __GFP_NOMEMALLOC).
> >
> > Please read my response again more carefully. I am not claiming that
> > combination is not allowed. I have said it doesn't make any sense in
> > this context.
> 
> I see you are worried that using GFP_ATOMIC will use reverse memory
> unlimited. So I think that __GFP_NOMEMALLOC may be suitable for us.
> Sorry, I may not understand the point you said. What I missed?

OK, let me try to explain again. GFP_ATOMIC is not only a non-sleeping
allocation request. It also grants access to memory reserves. The later
is a bit more involved because there are more layers of memory reserves
to access but that is not really important. Non-sleeping semantic can be
achieved by GFP_NOWAIT which will not grant access to reserves unless
explicitly stated - e.g. by __GFP_HIGH or __GFP_ATOMIC.
Is that more clear?

Now again why I do not think access to memory reserves is suitable.
Hugetlb pages can be released in a large batches and that might cause a
peak depletion of memory reserves which are normally used by other
consumers as well. Other GFP_ATOMIC users might see allocation failures.
Those shouldn't be really fatal as nobody should be relying on those and
a failure usually mean a hand over to a different, less constrained,
context. So this concern is more about a more well behaved behavior from
the hugetlb side than a correctness.
Is that more clear?

There shouldn't be any real reason why the memory allocation for
vmemmaps, or handling vmemmap in general, has to be done from within the
hugetlb lock and therefore requiring a non-sleeping semantic. All that
can be deferred to a more relaxed context. If you want to make a
GFP_NOWAIT optimistic attempt in the direct free path then no problem
but you have to expect failures under memory pressure. If you want to
have a more robust allocation request then you have to go outside of the
spin lock and use GFP_KERNEL | __GFP_NORETRY or GFP_KERNEL |
__GFP_RETRY_MAYFAIL depending on how hard you want to try.
__GFP_THISNODE makes a slight difference here but something that I would
recommend not depending on.
Is that more clear?
-- 
Michal Hocko
SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-15 13:19                 ` Michal Hocko
@ 2021-02-15 15:36                   ` Muchun Song
  2021-02-15 16:27                     ` Michal Hocko
  0 siblings, 1 reply; 37+ messages in thread
From: Muchun Song @ 2021-02-15 15:36 UTC (permalink / raw)
  To: Michal Hocko
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Mon, Feb 15, 2021 at 9:19 PM Michal Hocko <mhocko@suse.com> wrote:
>
> On Mon 15-02-21 20:44:57, Muchun Song wrote:
> > On Mon, Feb 15, 2021 at 8:18 PM Michal Hocko <mhocko@suse.com> wrote:
> > >
> > > On Mon 15-02-21 20:00:07, Muchun Song wrote:
> > > > On Mon, Feb 15, 2021 at 7:51 PM Muchun Song <songmuchun@bytedance.com> wrote:
> > > > >
> > > > > On Mon, Feb 15, 2021 at 6:33 PM Michal Hocko <mhocko@suse.com> wrote:
> > > > > >
> > > > > > On Mon 15-02-21 18:05:06, Muchun Song wrote:
> > > > > > > On Fri, Feb 12, 2021 at 11:32 PM Michal Hocko <mhocko@suse.com> wrote:
> > > > > > [...]
> > > > > > > > > +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 (!free_vmemmap_pages_per_hpage(h))
> > > > > > > > > +             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_ATOMIC | __GFP_NOWARN | __GFP_THISNODE);
> > > > > > > >
> > > > > > > > I do not think that this is a good allocation mode. GFP_ATOMIC is a non
> > > > > > > > sleeping allocation and a medium memory pressure might cause it to
> > > > > > > > fail prematurely. I do not think this is really an atomic context which
> > > > > > > > couldn't afford memory reclaim. I also do not think we want to grant
> > > > > > >
> > > > > > > Because alloc_huge_page_vmemmap is called under hugetlb_lock
> > > > > > > now. So using GFP_ATOMIC indeed makes the code more simpler.
> > > > > >
> > > > > > You can have a preallocated list of pages prior taking the lock.
> > > > >
> > > > > A discussion about this can refer to here:
> > > > >
> > > > > https://patchwork.kernel.org/project/linux-mm/patch/20210117151053.24600-5-songmuchun@bytedance.com/
> > > > >
> > > > > > Moreover do we want to manipulate vmemmaps from under spinlock in
> > > > > > general. I have to say I have missed that detail when reviewing. Need to
> > > > > > think more.
> > > > > >
> > > > > > > From the document of the kernel, I learned that __GFP_NOMEMALLOC
> > > > > > > can be used to explicitly forbid access to emergency reserves. So if
> > > > > > > we do not want to use the reserve memory. How about replacing it to
> > > > > > >
> > > > > > > GFP_ATOMIC | __GFP_NOMEMALLOC | __GFP_NOWARN | __GFP_THISNODE
> > > > > >
> > > > > > The whole point of GFP_ATOMIC is to grant access to memory reserves so
> > > > > > the above is quite dubious. If you do not want access to memory reserves
> > > > >
> > > > > Look at the code of gfp_to_alloc_flags().
> > > > >
> > > > > static inline unsigned int gfp_to_alloc_flags(gfp_t gfp_mask)
> > > > > {
> > > > >         [...]
> > > > >         if (gfp_mask & __GFP_ATOMIC) {
> > > > >         /*
> > > > >          * Not worth trying to allocate harder for __GFP_NOMEMALLOC even
> > > > >          * if it can't schedule.
> > > > >          */
> > > > >         if (!(gfp_mask & __GFP_NOMEMALLOC))
> > > > >                 alloc_flags |= ALLOC_HARDER;
> > > > >        [...]
> > > > > }
> > > > >
> > > > > Seems to allow this operation (GFP_ATOMIC | __GFP_NOMEMALLOC).
> > >
> > > Please read my response again more carefully. I am not claiming that
> > > combination is not allowed. I have said it doesn't make any sense in
> > > this context.
> >
> > I see you are worried that using GFP_ATOMIC will use reverse memory
> > unlimited. So I think that __GFP_NOMEMALLOC may be suitable for us.
> > Sorry, I may not understand the point you said. What I missed?
>
> OK, let me try to explain again. GFP_ATOMIC is not only a non-sleeping
> allocation request. It also grants access to memory reserves. The later
> is a bit more involved because there are more layers of memory reserves
> to access but that is not really important. Non-sleeping semantic can be
> achieved by GFP_NOWAIT which will not grant access to reserves unless
> explicitly stated - e.g. by __GFP_HIGH or __GFP_ATOMIC.
> Is that more clear?
>
> Now again why I do not think access to memory reserves is suitable.
> Hugetlb pages can be released in a large batches and that might cause a
> peak depletion of memory reserves which are normally used by other
> consumers as well. Other GFP_ATOMIC users might see allocation failures.
> Those shouldn't be really fatal as nobody should be relying on those and
> a failure usually mean a hand over to a different, less constrained,
> context. So this concern is more about a more well behaved behavior from
> the hugetlb side than a correctness.
> Is that more clear?

Ok. It is very clear. Very thanks for your patient explanations.

>
> There shouldn't be any real reason why the memory allocation for
> vmemmaps, or handling vmemmap in general, has to be done from within the
> hugetlb lock and therefore requiring a non-sleeping semantic. All that
> can be deferred to a more relaxed context. If you want to make a

Yeah, you are right. We can put the freeing hugetlb routine to a
workqueue. Just like I do in the previous version (before v13) patch.
I will pick up these patches.

> GFP_NOWAIT optimistic attempt in the direct free path then no problem
> but you have to expect failures under memory pressure. If you want to
> have a more robust allocation request then you have to go outside of the
> spin lock and use GFP_KERNEL | __GFP_NORETRY or GFP_KERNEL |
> __GFP_RETRY_MAYFAIL depending on how hard you want to try.
> __GFP_THISNODE makes a slight difference here but something that I would
> recommend not depending on.
> Is that more clear?

OK. I will use GFP_KERNEL instead of GFP_ATOMIC. Thanks for your
suggestions.


> --
> Michal Hocko
> SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-15 15:36                   ` Muchun Song
@ 2021-02-15 16:27                     ` Michal Hocko
  2021-02-15 17:48                       ` Muchun Song
  2021-02-16 19:44                       ` Mike Kravetz
  0 siblings, 2 replies; 37+ messages in thread
From: Michal Hocko @ 2021-02-15 16:27 UTC (permalink / raw)
  To: Muchun Song
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Mon 15-02-21 23:36:49, Muchun Song wrote:
[...]
> > There shouldn't be any real reason why the memory allocation for
> > vmemmaps, or handling vmemmap in general, has to be done from within the
> > hugetlb lock and therefore requiring a non-sleeping semantic. All that
> > can be deferred to a more relaxed context. If you want to make a
> 
> Yeah, you are right. We can put the freeing hugetlb routine to a
> workqueue. Just like I do in the previous version (before v13) patch.
> I will pick up these patches.

I haven't seen your v13 and I will unlikely have time to revisit that
version. I just wanted to point out that the actual allocation doesn't
have to happen from under the spinlock. There are multiple ways to go
around that. Dropping the lock would be one of them. Preallocation
before the spin lock is taken is another. WQ is certainly an option but
I would take it as the last resort when other paths are not feasible.

-- 
Michal Hocko
SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-15 16:27                     ` Michal Hocko
@ 2021-02-15 17:48                       ` Muchun Song
  2021-02-15 18:19                         ` Muchun Song
  2021-02-15 19:02                         ` Michal Hocko
  2021-02-16 19:44                       ` Mike Kravetz
  1 sibling, 2 replies; 37+ messages in thread
From: Muchun Song @ 2021-02-15 17:48 UTC (permalink / raw)
  To: Michal Hocko
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Tue, Feb 16, 2021 at 12:28 AM Michal Hocko <mhocko@suse.com> wrote:
>
> On Mon 15-02-21 23:36:49, Muchun Song wrote:
> [...]
> > > There shouldn't be any real reason why the memory allocation for
> > > vmemmaps, or handling vmemmap in general, has to be done from within the
> > > hugetlb lock and therefore requiring a non-sleeping semantic. All that
> > > can be deferred to a more relaxed context. If you want to make a
> >
> > Yeah, you are right. We can put the freeing hugetlb routine to a
> > workqueue. Just like I do in the previous version (before v13) patch.
> > I will pick up these patches.
>
> I haven't seen your v13 and I will unlikely have time to revisit that
> version. I just wanted to point out that the actual allocation doesn't
> have to happen from under the spinlock. There are multiple ways to go
> around that. Dropping the lock would be one of them. Preallocation
> before the spin lock is taken is another. WQ is certainly an option but
> I would take it as the last resort when other paths are not feasible.
>

"Dropping the lock" and "Preallocation before the spin lock" can limit
the context of put_page to non-atomic context. I am not sure if there
is a page puted somewhere under an atomic context. e.g. compaction.
I am not an expert on this.

> --
> Michal Hocko
> SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-15 17:48                       ` Muchun Song
@ 2021-02-15 18:19                         ` Muchun Song
  2021-02-15 19:39                           ` Michal Hocko
  2021-02-15 19:02                         ` Michal Hocko
  1 sibling, 1 reply; 37+ messages in thread
From: Muchun Song @ 2021-02-15 18:19 UTC (permalink / raw)
  To: Michal Hocko
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Tue, Feb 16, 2021 at 1:48 AM Muchun Song <songmuchun@bytedance.com> wrote:
>
> On Tue, Feb 16, 2021 at 12:28 AM Michal Hocko <mhocko@suse.com> wrote:
> >
> > On Mon 15-02-21 23:36:49, Muchun Song wrote:
> > [...]
> > > > There shouldn't be any real reason why the memory allocation for
> > > > vmemmaps, or handling vmemmap in general, has to be done from within the
> > > > hugetlb lock and therefore requiring a non-sleeping semantic. All that
> > > > can be deferred to a more relaxed context. If you want to make a
> > >
> > > Yeah, you are right. We can put the freeing hugetlb routine to a
> > > workqueue. Just like I do in the previous version (before v13) patch.
> > > I will pick up these patches.
> >
> > I haven't seen your v13 and I will unlikely have time to revisit that
> > version. I just wanted to point out that the actual allocation doesn't
> > have to happen from under the spinlock. There are multiple ways to go
> > around that. Dropping the lock would be one of them. Preallocation
> > before the spin lock is taken is another. WQ is certainly an option but
> > I would take it as the last resort when other paths are not feasible.
> >
>
> "Dropping the lock" and "Preallocation before the spin lock" can limit
> the context of put_page to non-atomic context. I am not sure if there
> is a page puted somewhere under an atomic context. e.g. compaction.
> I am not an expert on this.

Using GFP_KERNEL will also use the current task cpuset to allocate
memory. Do we have an interface to ignore current task cpuset?If not,
WQ may be the only option and it also will not limit the context of
put_page. Right?

>
> > --
> > Michal Hocko
> > SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-15 17:48                       ` Muchun Song
  2021-02-15 18:19                         ` Muchun Song
@ 2021-02-15 19:02                         ` Michal Hocko
  2021-02-16  8:13                           ` David Hildenbrand
  1 sibling, 1 reply; 37+ messages in thread
From: Michal Hocko @ 2021-02-15 19:02 UTC (permalink / raw)
  To: Muchun Song
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Tue 16-02-21 01:48:29, Muchun Song wrote:
> On Tue, Feb 16, 2021 at 12:28 AM Michal Hocko <mhocko@suse.com> wrote:
> >
> > On Mon 15-02-21 23:36:49, Muchun Song wrote:
> > [...]
> > > > There shouldn't be any real reason why the memory allocation for
> > > > vmemmaps, or handling vmemmap in general, has to be done from within the
> > > > hugetlb lock and therefore requiring a non-sleeping semantic. All that
> > > > can be deferred to a more relaxed context. If you want to make a
> > >
> > > Yeah, you are right. We can put the freeing hugetlb routine to a
> > > workqueue. Just like I do in the previous version (before v13) patch.
> > > I will pick up these patches.
> >
> > I haven't seen your v13 and I will unlikely have time to revisit that
> > version. I just wanted to point out that the actual allocation doesn't
> > have to happen from under the spinlock. There are multiple ways to go
> > around that. Dropping the lock would be one of them. Preallocation
> > before the spin lock is taken is another. WQ is certainly an option but
> > I would take it as the last resort when other paths are not feasible.
> >
> 
> "Dropping the lock" and "Preallocation before the spin lock" can limit
> the context of put_page to non-atomic context. I am not sure if there
> is a page puted somewhere under an atomic context. e.g. compaction.
> I am not an expert on this.

Then do a due research or ask for a help from the MM community. Do
not just try to go around harder problems and somehow duct tape a
solution. I am sorry for sounding harsh here but this is a repetitive
pattern.

Now to the merit. put_page can indeed be called from all sorts of
contexts. And it might be indeed impossible to guarantee that hugetlb
pages are never freed up from an atomic context. Requiring that would be
even hard to maintain longterm. There are ways around that, I believe,
though.

The most simple one that I can think of right now would be using
in_atomic() rather than in_task() check free_huge_page. IIRC recent
changes would allow in_atomic to be reliable also on !PREEMPT kernels
(via RCU tree, not sure where this stands right now). That would make
__free_huge_page always run in a non-atomic context which sounds like an
easy enough solution.
Another way would be to keep a pool of ready pages to use in case of
GFP_NOWAIT allocation fails and have means to keep that pool replenished
when needed. Would it be feasible to reused parts of the freed page in
the worst case?

-- 
Michal Hocko
SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-15 18:19                         ` Muchun Song
@ 2021-02-15 19:39                           ` Michal Hocko
  2021-02-16  4:34                             ` Muchun Song
  0 siblings, 1 reply; 37+ messages in thread
From: Michal Hocko @ 2021-02-15 19:39 UTC (permalink / raw)
  To: Muchun Song
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Tue 16-02-21 02:19:20, Muchun Song wrote:
> On Tue, Feb 16, 2021 at 1:48 AM Muchun Song <songmuchun@bytedance.com> wrote:
> >
> > On Tue, Feb 16, 2021 at 12:28 AM Michal Hocko <mhocko@suse.com> wrote:
> > >
> > > On Mon 15-02-21 23:36:49, Muchun Song wrote:
> > > [...]
> > > > > There shouldn't be any real reason why the memory allocation for
> > > > > vmemmaps, or handling vmemmap in general, has to be done from within the
> > > > > hugetlb lock and therefore requiring a non-sleeping semantic. All that
> > > > > can be deferred to a more relaxed context. If you want to make a
> > > >
> > > > Yeah, you are right. We can put the freeing hugetlb routine to a
> > > > workqueue. Just like I do in the previous version (before v13) patch.
> > > > I will pick up these patches.
> > >
> > > I haven't seen your v13 and I will unlikely have time to revisit that
> > > version. I just wanted to point out that the actual allocation doesn't
> > > have to happen from under the spinlock. There are multiple ways to go
> > > around that. Dropping the lock would be one of them. Preallocation
> > > before the spin lock is taken is another. WQ is certainly an option but
> > > I would take it as the last resort when other paths are not feasible.
> > >
> >
> > "Dropping the lock" and "Preallocation before the spin lock" can limit
> > the context of put_page to non-atomic context. I am not sure if there
> > is a page puted somewhere under an atomic context. e.g. compaction.
> > I am not an expert on this.
> 
> Using GFP_KERNEL will also use the current task cpuset to allocate
> memory. Do we have an interface to ignore current task cpuset?If not,
> WQ may be the only option and it also will not limit the context of
> put_page. Right?

Well, GFP_KERNEL is constrained to the task cpuset only if the said
cpuset is hardwalled IIRC. But I do not see why this is a problem.
-- 
Michal Hocko
SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-15 19:39                           ` Michal Hocko
@ 2021-02-16  4:34                             ` Muchun Song
  2021-02-16  8:15                               ` Michal Hocko
  0 siblings, 1 reply; 37+ messages in thread
From: Muchun Song @ 2021-02-16  4:34 UTC (permalink / raw)
  To: Michal Hocko
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Tue, Feb 16, 2021 at 3:39 AM Michal Hocko <mhocko@suse.com> wrote:
>
> On Tue 16-02-21 02:19:20, Muchun Song wrote:
> > On Tue, Feb 16, 2021 at 1:48 AM Muchun Song <songmuchun@bytedance.com> wrote:
> > >
> > > On Tue, Feb 16, 2021 at 12:28 AM Michal Hocko <mhocko@suse.com> wrote:
> > > >
> > > > On Mon 15-02-21 23:36:49, Muchun Song wrote:
> > > > [...]
> > > > > > There shouldn't be any real reason why the memory allocation for
> > > > > > vmemmaps, or handling vmemmap in general, has to be done from within the
> > > > > > hugetlb lock and therefore requiring a non-sleeping semantic. All that
> > > > > > can be deferred to a more relaxed context. If you want to make a
> > > > >
> > > > > Yeah, you are right. We can put the freeing hugetlb routine to a
> > > > > workqueue. Just like I do in the previous version (before v13) patch.
> > > > > I will pick up these patches.
> > > >
> > > > I haven't seen your v13 and I will unlikely have time to revisit that
> > > > version. I just wanted to point out that the actual allocation doesn't
> > > > have to happen from under the spinlock. There are multiple ways to go
> > > > around that. Dropping the lock would be one of them. Preallocation
> > > > before the spin lock is taken is another. WQ is certainly an option but
> > > > I would take it as the last resort when other paths are not feasible.
> > > >
> > >
> > > "Dropping the lock" and "Preallocation before the spin lock" can limit
> > > the context of put_page to non-atomic context. I am not sure if there
> > > is a page puted somewhere under an atomic context. e.g. compaction.
> > > I am not an expert on this.
> >
> > Using GFP_KERNEL will also use the current task cpuset to allocate
> > memory. Do we have an interface to ignore current task cpuset?If not,
> > WQ may be the only option and it also will not limit the context of
> > put_page. Right?
>
> Well, GFP_KERNEL is constrained to the task cpuset only if the said
> cpuset is hardwalled IIRC. But I do not see why this is a problem.

I mean that if there are more than one node in the system,
but the current task cpuset only allows one node. If current
node has no memory and other nodes have enough memory.
We can fail to allocate vmemmap pages. But actually it is
suitable to allocate vmemmap pages from other nodes.
Right?

Thanks.

> --
> Michal Hocko
> SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-15 19:02                         ` Michal Hocko
@ 2021-02-16  8:13                           ` David Hildenbrand
  2021-02-16  8:21                             ` Michal Hocko
  0 siblings, 1 reply; 37+ messages in thread
From: David Hildenbrand @ 2021-02-16  8:13 UTC (permalink / raw)
  To: Michal Hocko, Muchun Song
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On 15.02.21 20:02, Michal Hocko wrote:
> On Tue 16-02-21 01:48:29, Muchun Song wrote:
>> On Tue, Feb 16, 2021 at 12:28 AM Michal Hocko <mhocko@suse.com> wrote:
>>>
>>> On Mon 15-02-21 23:36:49, Muchun Song wrote:
>>> [...]
>>>>> There shouldn't be any real reason why the memory allocation for
>>>>> vmemmaps, or handling vmemmap in general, has to be done from within the
>>>>> hugetlb lock and therefore requiring a non-sleeping semantic. All that
>>>>> can be deferred to a more relaxed context. If you want to make a
>>>>
>>>> Yeah, you are right. We can put the freeing hugetlb routine to a
>>>> workqueue. Just like I do in the previous version (before v13) patch.
>>>> I will pick up these patches.
>>>
>>> I haven't seen your v13 and I will unlikely have time to revisit that
>>> version. I just wanted to point out that the actual allocation doesn't
>>> have to happen from under the spinlock. There are multiple ways to go
>>> around that. Dropping the lock would be one of them. Preallocation
>>> before the spin lock is taken is another. WQ is certainly an option but
>>> I would take it as the last resort when other paths are not feasible.
>>>
>>
>> "Dropping the lock" and "Preallocation before the spin lock" can limit
>> the context of put_page to non-atomic context. I am not sure if there
>> is a page puted somewhere under an atomic context. e.g. compaction.
>> I am not an expert on this.
> 
> Then do a due research or ask for a help from the MM community. Do
> not just try to go around harder problems and somehow duct tape a
> solution. I am sorry for sounding harsh here but this is a repetitive
> pattern.
> 
> Now to the merit. put_page can indeed be called from all sorts of
> contexts. And it might be indeed impossible to guarantee that hugetlb
> pages are never freed up from an atomic context. Requiring that would be
> even hard to maintain longterm. There are ways around that, I believe,
> though.
> 
> The most simple one that I can think of right now would be using
> in_atomic() rather than in_task() check free_huge_page. IIRC recent
> changes would allow in_atomic to be reliable also on !PREEMPT kernels
> (via RCU tree, not sure where this stands right now). That would make
> __free_huge_page always run in a non-atomic context which sounds like an
> easy enough solution.
> Another way would be to keep a pool of ready pages to use in case of
> GFP_NOWAIT allocation fails and have means to keep that pool replenished
> when needed. Would it be feasible to reused parts of the freed page in
> the worst case?

As already discussed, this is only possible when the huge page does not 
reside on ZONE_MOVABLE/CMA.

In addition, we can no longer form a huge page at that memory location ever.

-- 
Thanks,

David / dhildenb



^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-16  4:34                             ` Muchun Song
@ 2021-02-16  8:15                               ` Michal Hocko
  2021-02-16  8:20                                 ` David Hildenbrand
  2021-02-16  9:03                                 ` Muchun Song
  0 siblings, 2 replies; 37+ messages in thread
From: Michal Hocko @ 2021-02-16  8:15 UTC (permalink / raw)
  To: Muchun Song
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Tue 16-02-21 12:34:41, Muchun Song wrote:
> On Tue, Feb 16, 2021 at 3:39 AM Michal Hocko <mhocko@suse.com> wrote:
[...]
> > > Using GFP_KERNEL will also use the current task cpuset to allocate
> > > memory. Do we have an interface to ignore current task cpuset?If not,
> > > WQ may be the only option and it also will not limit the context of
> > > put_page. Right?
> >
> > Well, GFP_KERNEL is constrained to the task cpuset only if the said
> > cpuset is hardwalled IIRC. But I do not see why this is a problem.
> 
> I mean that if there are more than one node in the system,
> but the current task cpuset only allows one node.

How would that cpuset get a huge pages from a node which is not part of
the cpuset? Well, that would be possible if the cpuset was dynamic but I
am not sure that such a configuration would be very sensible along with
hardwall setup.

> If current
> node has no memory and other nodes have enough memory.
> We can fail to allocate vmemmap pages. But actually it is
> suitable to allocate vmemmap pages from other nodes.
> Right?

Falling back to a different node would be very suboptimal because then
you would have vmemmap back by remote pages. We do not want that.
-- 
Michal Hocko
SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-16  8:15                               ` Michal Hocko
@ 2021-02-16  8:20                                 ` David Hildenbrand
  2021-02-16  9:03                                 ` Muchun Song
  1 sibling, 0 replies; 37+ messages in thread
From: David Hildenbrand @ 2021-02-16  8:20 UTC (permalink / raw)
  To: Michal Hocko, Muchun Song
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

>> If current
>> node has no memory and other nodes have enough memory.
>> We can fail to allocate vmemmap pages. But actually it is
>> suitable to allocate vmemmap pages from other nodes.
>> Right?
> 
> Falling back to a different node would be very suboptimal because then
> you would have vmemmap back by remote pages. We do not want that.

... and we even warn when this happens right now:

mm/sparse-vmemmap.c:vmemmap_verify()

-- 
Thanks,

David / dhildenb



^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-16  8:13                           ` David Hildenbrand
@ 2021-02-16  8:21                             ` Michal Hocko
  0 siblings, 0 replies; 37+ messages in thread
From: Michal Hocko @ 2021-02-16  8:21 UTC (permalink / raw)
  To: David Hildenbrand
  Cc: Muchun Song, Jonathan Corbet, Mike Kravetz, Thomas Gleixner,
	mingo, bp, x86, hpa, dave.hansen, luto, Peter Zijlstra, viro,
	Andrew Morton, paulmck, mchehab+huawei, pawan.kumar.gupta,
	Randy Dunlap, oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Tue 16-02-21 09:13:09, David Hildenbrand wrote:
> On 15.02.21 20:02, Michal Hocko wrote:
> > Would it be feasible to reused parts of the freed page in
> > the worst case?
> 
> As already discussed, this is only possible when the huge page does not
> reside on ZONE_MOVABLE/CMA.

Right. But usually this is not the case so it would be at least
something.

> In addition, we can no longer form a huge page at that memory location ever.

Yes, that's why I am saying in the worst case. E.g. when dissolving is
really necessary like in hwpoison case.

Maybe we are really far from needing something like that. I just wanted
to mention this option and I was not aware this has been discussed
previously.
-- 
Michal Hocko
SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-16  8:15                               ` Michal Hocko
  2021-02-16  8:20                                 ` David Hildenbrand
@ 2021-02-16  9:03                                 ` Muchun Song
  1 sibling, 0 replies; 37+ messages in thread
From: Muchun Song @ 2021-02-16  9:03 UTC (permalink / raw)
  To: Michal Hocko
  Cc: Jonathan Corbet, Mike Kravetz, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Tue, Feb 16, 2021 at 4:15 PM Michal Hocko <mhocko@suse.com> wrote:
>
> On Tue 16-02-21 12:34:41, Muchun Song wrote:
> > On Tue, Feb 16, 2021 at 3:39 AM Michal Hocko <mhocko@suse.com> wrote:
> [...]
> > > > Using GFP_KERNEL will also use the current task cpuset to allocate
> > > > memory. Do we have an interface to ignore current task cpuset?If not,
> > > > WQ may be the only option and it also will not limit the context of
> > > > put_page. Right?
> > >
> > > Well, GFP_KERNEL is constrained to the task cpuset only if the said
> > > cpuset is hardwalled IIRC. But I do not see why this is a problem.
> >
> > I mean that if there are more than one node in the system,
> > but the current task cpuset only allows one node.
>
> How would that cpuset get a huge pages from a node which is not part of
> the cpuset? Well, that would be possible if the cpuset was dynamic but I
> am not sure that such a configuration would be very sensible along with
> hardwall setup.

Got it. I didn't realize this before. Thanks.

>
> > If current
> > node has no memory and other nodes have enough memory.
> > We can fail to allocate vmemmap pages. But actually it is
> > suitable to allocate vmemmap pages from other nodes.
> > Right?
>
> Falling back to a different node would be very suboptimal because then
> you would have vmemmap back by remote pages. We do not want that.
> --
> Michal Hocko
> SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-15 16:27                     ` Michal Hocko
  2021-02-15 17:48                       ` Muchun Song
@ 2021-02-16 19:44                       ` Mike Kravetz
  2021-02-17  8:13                         ` Michal Hocko
  1 sibling, 1 reply; 37+ messages in thread
From: Mike Kravetz @ 2021-02-16 19:44 UTC (permalink / raw)
  To: Michal Hocko, Muchun Song
  Cc: Jonathan Corbet, Thomas Gleixner, mingo, bp, x86, hpa,
	dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton, paulmck,
	mchehab+huawei, pawan.kumar.gupta, Randy Dunlap, oneukum,
	anshuman.khandual, jroedel, Mina Almasry, David Rientjes,
	Matthew Wilcox, Oscar Salvador, Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On 2/15/21 8:27 AM, Michal Hocko wrote:
> On Mon 15-02-21 23:36:49, Muchun Song wrote:
> [...]
>>> There shouldn't be any real reason why the memory allocation for
>>> vmemmaps, or handling vmemmap in general, has to be done from within the
>>> hugetlb lock and therefore requiring a non-sleeping semantic. All that
>>> can be deferred to a more relaxed context. If you want to make a
>>
>> Yeah, you are right. We can put the freeing hugetlb routine to a
>> workqueue. Just like I do in the previous version (before v13) patch.
>> I will pick up these patches.
> 
> I haven't seen your v13 and I will unlikely have time to revisit that
> version. I just wanted to point out that the actual allocation doesn't
> have to happen from under the spinlock. There are multiple ways to go
> around that. Dropping the lock would be one of them. Preallocation
> before the spin lock is taken is another. WQ is certainly an option but
> I would take it as the last resort when other paths are not feasible.

Sorry for jumping in late, Monday was a US holiday ...

IIRC, the point of moving the vmemmap allocations under the hugetlb_lock
was just for simplicity.  The idea was to modify the allocations to be
non-blocking so that allocating pages and restoring vmemmap could be done
as part of normal huge page freeing where we are holding the lock.  Perhaps
that is too simplistic of an approach.

IMO, using the workque approach as done in previous patches introduces
too much complexity.

Michal did bring up the question "Do we really want to do all the vmemmap
allocation (even non-blocking) and manipulation under the hugetlb lock?
I'm thinking the answer may be no.  For 1G pages, this will require 4094
calls to alloc_pages.  Even with non-blocking calls this seems like a long
time.

If we are not going to do the allocations under the lock, then we will need
to either preallocate or take the workqueue approach.  One complication with
preallocation is that we do not for sure we will be freeing the huge page
to buddy until we take the hugetlb_lock.  This is because the decision to
free or not is based on counters protected by the lock.  We could of course
check counters without the lock to guess if we will be freeing the page,
and then check again after acquiring the lock.  This may not be too bad in
the case of freeing a single page, but would become more complex when doing
bulk freeing.  After a little thought, the workqueue approach may even end
up simpler.  However, I would suggest a very simple workqueue implementation
with non-blocking allocations.  If we can not quickly get vmemmap pages,
put the page back on the hugetlb free list and treat as a surplus page.
-- 
Mike Kravetz


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-16 19:44                       ` Mike Kravetz
@ 2021-02-17  8:13                         ` Michal Hocko
  2021-02-18  1:00                           ` Mike Kravetz
  0 siblings, 1 reply; 37+ messages in thread
From: Michal Hocko @ 2021-02-17  8:13 UTC (permalink / raw)
  To: Mike Kravetz
  Cc: Muchun Song, Jonathan Corbet, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Tue 16-02-21 11:44:34, Mike Kravetz wrote:
[...]
> If we are not going to do the allocations under the lock, then we will need
> to either preallocate or take the workqueue approach.

We can still drop the lock temporarily right? As we already do before
calling destroy_compound_gigantic_page...

-- 
Michal Hocko
SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-17  8:13                         ` Michal Hocko
@ 2021-02-18  1:00                           ` Mike Kravetz
  2021-02-18  3:20                             ` Muchun Song
  0 siblings, 1 reply; 37+ messages in thread
From: Mike Kravetz @ 2021-02-18  1:00 UTC (permalink / raw)
  To: Michal Hocko
  Cc: Muchun Song, Jonathan Corbet, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On 2/17/21 12:13 AM, Michal Hocko wrote:
> On Tue 16-02-21 11:44:34, Mike Kravetz wrote:
> [...]
>> If we are not going to do the allocations under the lock, then we will need
>> to either preallocate or take the workqueue approach.
> 
> We can still drop the lock temporarily right? As we already do before
> calling destroy_compound_gigantic_page...
> 

Yes we can.  I forgot about that.

Actually, very little of what update_and_free_page does needs to be done
under the lock.  Perhaps, just decrementing the global count and clearing
the destructor so PageHuge() is no longer true.
-- 
Mike Kravetz


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-18  1:00                           ` Mike Kravetz
@ 2021-02-18  3:20                             ` Muchun Song
  2021-02-18  8:21                               ` Michal Hocko
  0 siblings, 1 reply; 37+ messages in thread
From: Muchun Song @ 2021-02-18  3:20 UTC (permalink / raw)
  To: Mike Kravetz, Michal Hocko
  Cc: Jonathan Corbet, Thomas Gleixner, mingo, bp, x86, hpa,
	dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton, paulmck,
	mchehab+huawei, pawan.kumar.gupta, Randy Dunlap, oneukum,
	anshuman.khandual, jroedel, Mina Almasry, David Rientjes,
	Matthew Wilcox, Oscar Salvador, Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Thu, Feb 18, 2021 at 9:00 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 2/17/21 12:13 AM, Michal Hocko wrote:
> > On Tue 16-02-21 11:44:34, Mike Kravetz wrote:
> > [...]
> >> If we are not going to do the allocations under the lock, then we will need
> >> to either preallocate or take the workqueue approach.
> >
> > We can still drop the lock temporarily right? As we already do before
> > calling destroy_compound_gigantic_page...
> >
>
> Yes we can.  I forgot about that.
>
> Actually, very little of what update_and_free_page does needs to be done
> under the lock.  Perhaps, just decrementing the global count and clearing
> the destructor so PageHuge() is no longer true.

Right. I have another question about using GFP flags. Michal
suggested using GFP_KERNEL instead of GFP_ATOMIC to
save reserve memory. From your last email, you suggested
using non-blocking allocation GFP flags (perhaps GFP_NOWAIT).

Hi Mike and Michal,

What is the consensus we finally reached? Thanks.


^ permalink raw reply	[flat|nested] 37+ messages in thread

* Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
  2021-02-18  3:20                             ` Muchun Song
@ 2021-02-18  8:21                               ` Michal Hocko
  0 siblings, 0 replies; 37+ messages in thread
From: Michal Hocko @ 2021-02-18  8:21 UTC (permalink / raw)
  To: Muchun Song
  Cc: Mike Kravetz, Jonathan Corbet, Thomas Gleixner, mingo, bp, x86,
	hpa, dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton,
	paulmck, mchehab+huawei, pawan.kumar.gupta, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, Matthew Wilcox, Oscar Salvador,
	Song Bao Hua (Barry Song),
	David Hildenbrand,
	HORIGUCHI NAOYA(堀口 直也),
	Joao Martins, Xiongchun duan, linux-doc, LKML,
	Linux Memory Management List, linux-fsdevel

On Thu 18-02-21 11:20:51, Muchun Song wrote:
> On Thu, Feb 18, 2021 at 9:00 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
> >
> > On 2/17/21 12:13 AM, Michal Hocko wrote:
> > > On Tue 16-02-21 11:44:34, Mike Kravetz wrote:
> > > [...]
> > >> If we are not going to do the allocations under the lock, then we will need
> > >> to either preallocate or take the workqueue approach.
> > >
> > > We can still drop the lock temporarily right? As we already do before
> > > calling destroy_compound_gigantic_page...
> > >
> >
> > Yes we can.  I forgot about that.
> >
> > Actually, very little of what update_and_free_page does needs to be done
> > under the lock.  Perhaps, just decrementing the global count and clearing
> > the destructor so PageHuge() is no longer true.
> 
> Right. I have another question about using GFP flags. Michal
> suggested using GFP_KERNEL instead of GFP_ATOMIC to
> save reserve memory. From your last email, you suggested
> using non-blocking allocation GFP flags (perhaps GFP_NOWAIT).
> 
> Hi Mike and Michal,
> 
> What is the consensus we finally reached? Thanks.

If the lock can be dropped and you make sure the final put on page is
not called from an atomic context then use (for starter)
GFP_KERNEL | __GFP_NORETRY | __GFP_THISNODE. I have intentionaly dropped
__GFP_NOWARN because likely want to hear about the failure so that we
can evaluate how often this happens.

This would be my recommendation.
-- 
Michal Hocko
SUSE Labs


^ permalink raw reply	[flat|nested] 37+ messages in thread

end of thread, other threads:[~2021-02-18  8:21 UTC | newest]

Thread overview: 37+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-02-08  8:50 [PATCH v15 0/8] Free some vmemmap pages of HugeTLB page Muchun Song
2021-02-08  8:50 ` [PATCH v15 1/8] mm: memory_hotplug: factor out bootmem core functions to bootmem_info.c Muchun Song
2021-02-08  8:50 ` [PATCH v15 2/8] mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
2021-02-08  8:50 ` [PATCH v15 3/8] mm: hugetlb: free the vmemmap pages associated with each HugeTLB page Muchun Song
2021-02-08  8:50 ` [PATCH v15 4/8] mm: hugetlb: alloc " Muchun Song
2021-02-11 18:05   ` Mike Kravetz
2021-02-12 14:15     ` David Hildenbrand
2021-02-12 15:32   ` Michal Hocko
2021-02-15 10:05     ` [External] " Muchun Song
2021-02-15 10:33       ` Michal Hocko
2021-02-15 11:51         ` Muchun Song
2021-02-15 12:00           ` Muchun Song
2021-02-15 12:18             ` Michal Hocko
2021-02-15 12:44               ` Muchun Song
2021-02-15 13:19                 ` Michal Hocko
2021-02-15 15:36                   ` Muchun Song
2021-02-15 16:27                     ` Michal Hocko
2021-02-15 17:48                       ` Muchun Song
2021-02-15 18:19                         ` Muchun Song
2021-02-15 19:39                           ` Michal Hocko
2021-02-16  4:34                             ` Muchun Song
2021-02-16  8:15                               ` Michal Hocko
2021-02-16  8:20                                 ` David Hildenbrand
2021-02-16  9:03                                 ` Muchun Song
2021-02-15 19:02                         ` Michal Hocko
2021-02-16  8:13                           ` David Hildenbrand
2021-02-16  8:21                             ` Michal Hocko
2021-02-16 19:44                       ` Mike Kravetz
2021-02-17  8:13                         ` Michal Hocko
2021-02-18  1:00                           ` Mike Kravetz
2021-02-18  3:20                             ` Muchun Song
2021-02-18  8:21                               ` Michal Hocko
2021-02-15 12:24           ` Michal Hocko
2021-02-08  8:50 ` [PATCH v15 5/8] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap Muchun Song
2021-02-08  8:50 ` [PATCH v15 6/8] mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate Muchun Song
2021-02-08  8:50 ` [PATCH v15 7/8] mm: hugetlb: gather discrete indexes of tail page Muchun Song
2021-02-08  8:50 ` [PATCH v15 8/8] mm: hugetlb: optimize the code with the help of the compiler Muchun Song

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