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* [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page
@ 2020-09-15 12:59 Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 01/24] mm/memory_hotplug: Move bootmem info registration API to bootmem_info.c Muchun Song
                   ` (25 more replies)
  0 siblings, 26 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: 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.

Nowadays we track the status of physical page frames using `struct page`
arranged in one or more arrays. And here exists one-to-one mapping between
the physical page frame and the corresponding `struct page`.

The hugetlbpage support is built on top of multiple page size support
that is provided by most modern architectures. For example, x86 CPUs
normally support 4K and 2M (1G if architecturally supported) page sizes.
Every hugetlbpage has more than one `struct page`. The 2M hugetlbpage
has 512 `struct page` and 1G hugetlbpage has 4096 `struct page`. But
in the core of hugetlbpage only uses the first 4 `struct page` to store
metadata associated with each hugetlbpage. The rest of the `struct page`
are usually read the compound_head field which are all the same value.
If we can free some struct page memory to buddy system so that We can
save a lot of memory.

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

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


When a hugetlbpage is preallocated, we can change the mapping from above to
bellow.

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

The mapping of the first page(index 0) and the second page(index 1) is
unchanged. The remaining 6 pages are all mapped to the same page(index
1). So we only need 2 pages for vmemmap area and free 6 pages to the
buddy system to save memory. Why we can do this? Because the content
of the remaining 7 pages are usually same except the first page.

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

If we uses the 1G hugetlbpage, we can save 4095 pages. This is a very
substantial gain. On our server, run some SPDK applications which will
use 300GB hugetlbpage. With this feature enabled, we can save 4797MB
memory.

Muchun Song (24):
  mm/memory_hotplug: Move bootmem info registration API to
    bootmem_info.c
  mm/memory_hotplug: Move {get,put}_page_bootmem() to bootmem_info.c
  mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP
  mm/hugetlb: Register bootmem info when
    CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
  mm/hugetlb: Introduce nr_free_vmemmap_pages in the struct hstate
  mm/hugetlb: Introduce pgtable allocation/freeing helpers
  mm/hugetlb: Add freeing unused vmemmap pages support for x86
  mm/bootmem_info: Introduce {free,prepare}_vmemmap_page()
  x86/mm: Introduce VMEMMAP_SIZE/VMEMMAP_END macro
  mm/hugetlb: Free the vmemmap pages associated with each hugetlb page
  mm/hugetlb: Add vmemmap_pmd_huge macro for x86
  mm/hugetlb: Defer freeing of hugetlb pages
  mm/hugetlb: Allocate the vmemmap pages associated with each hugetlb
    page
  mm/hugetlb: Introduce remap_huge_page_pmd_vmemmap helper
  mm/hugetlb: Use PG_slab to indicate split pmd
  mm/hugetlb: Support freeing vmemmap pages of gigantic page
  mm/hugetlb: Add a BUILD_BUG_ON to check if struct page size is a power
    of two
  mm/hugetlb: Clear PageHWPoison on the non-error memory page
  mm/hugetlb: Flush work when dissolving hugetlb page
  mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap
  mm/hugetlb: Merge pte to huge pmd only for gigantic page
  mm/hugetlb: Implement vmemmap_pmd_mkhuge macro
  mm/hugetlb: Gather discrete indexes of tail page
  mm/hugetlb: Add BUILD_BUG_ON to catch invalid usage of tail struct
    page

 .../admin-guide/kernel-parameters.txt         |   9 +
 Documentation/admin-guide/mm/hugetlbpage.rst  |   3 +
 arch/x86/include/asm/hugetlb.h                |  20 +
 arch/x86/include/asm/pgtable_64_types.h       |   8 +
 arch/x86/mm/init_64.c                         |   5 +-
 fs/Kconfig                                    |  15 +
 include/linux/bootmem_info.h                  |  65 ++
 include/linux/hugetlb.h                       |  64 ++
 include/linux/hugetlb_cgroup.h                |  15 +-
 include/linux/memory_hotplug.h                |  27 -
 mm/Makefile                                   |   1 +
 mm/bootmem_info.c                             | 125 +++
 mm/hugetlb.c                                  | 834 +++++++++++++++++-
 mm/memory_hotplug.c                           | 116 ---
 mm/sparse.c                                   |   1 +
 15 files changed, 1143 insertions(+), 165 deletions(-)
 create mode 100644 include/linux/bootmem_info.h
 create mode 100644 mm/bootmem_info.c

-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 01/24] mm/memory_hotplug: Move bootmem info registration API to bootmem_info.c
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-29 22:46   ` Mike Kravetz
  2020-09-15 12:59 ` [RFC PATCH 02/24] mm/memory_hotplug: Move {get,put}_page_bootmem() " Muchun Song
                   ` (24 subsequent siblings)
  25 siblings, 1 reply; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

Move bootmem info registration common API to individual bootmem_info.c
for later patch use.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 arch/x86/mm/init_64.c          |  1 +
 include/linux/bootmem_info.h   | 27 ++++++++++
 include/linux/memory_hotplug.h | 23 --------
 mm/Makefile                    |  1 +
 mm/bootmem_info.c              | 99 ++++++++++++++++++++++++++++++++++
 mm/memory_hotplug.c            | 91 +------------------------------
 6 files changed, 129 insertions(+), 113 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..c7f7ad55b625 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>
diff --git a/include/linux/bootmem_info.h b/include/linux/bootmem_info.h
new file mode 100644
index 000000000000..65bb9b23140f
--- /dev/null
+++ b/include/linux/bootmem_info.h
@@ -0,0 +1,27 @@
+/* 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);
+#else
+static inline void register_page_bootmem_info_node(struct pglist_data *pgdat)
+{
+}
+#endif
+
+#endif /* __LINUX_BOOTMEM_INFO_H */
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 51a877fec8da..19e5d067294c 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -33,18 +33,6 @@ struct vmem_altmap;
 	___page;						   \
 })
 
-/*
- * 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. */
@@ -209,13 +197,6 @@ 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);
@@ -254,10 +235,6 @@ static inline int mhp_notimplemented(const char *func)
 	return -ENOSYS;
 }
 
-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 d5649f1c12c0..752111587c99 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -82,6 +82,7 @@ obj-$(CONFIG_SLAB) += slab.o
 obj-$(CONFIG_SLUB) += slub.o
 obj-$(CONFIG_KASAN)	+= kasan/
 obj-$(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..39fa8fc120bc
--- /dev/null
+++ b/mm/bootmem_info.c
@@ -0,0 +1,99 @@
+// 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>
+
+#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 baded53b9ff9..2da4ad071456 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -21,6 +21,7 @@
 #include <linux/memory.h>
 #include <linux/memremap.h>
 #include <linux/memory_hotplug.h>
+#include <linux/bootmem_info.h>
 #include <linux/highmem.h>
 #include <linux/vmalloc.h>
 #include <linux/ioport.h>
@@ -167,96 +168,6 @@ void put_page_bootmem(struct 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)
 {
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 02/24] mm/memory_hotplug: Move {get,put}_page_bootmem() to bootmem_info.c
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 01/24] mm/memory_hotplug: Move bootmem info registration API to bootmem_info.c Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-29 23:30   ` Mike Kravetz
  2020-09-15 12:59 ` [RFC PATCH 03/24] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
                   ` (23 subsequent siblings)
  25 siblings, 1 reply; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

In the later patch, we will use {get,put}_page_bootmem() to initialize
the page for vmemmap or free vmemmap page to buddy. So move them out of
CONFIG_MEMORY_HOTPLUG_SPARSE.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 arch/x86/mm/init_64.c          |  2 +-
 include/linux/bootmem_info.h   | 13 +++++++++++++
 include/linux/memory_hotplug.h |  4 ----
 mm/bootmem_info.c              | 26 ++++++++++++++++++++++++++
 mm/memory_hotplug.c            | 27 ---------------------------
 mm/sparse.c                    |  1 +
 6 files changed, 41 insertions(+), 32 deletions(-)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index c7f7ad55b625..0a45f062826e 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1572,7 +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
index 65bb9b23140f..4ed6dee1adc9 100644
--- a/include/linux/bootmem_info.h
+++ b/include/linux/bootmem_info.h
@@ -18,10 +18,23 @@ enum {
 
 #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 19e5d067294c..c9f3361fe84b 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -197,10 +197,6 @@ static inline void arch_refresh_nodedata(int nid, pg_data_t *pgdat)
 #endif /* CONFIG_NUMA */
 #endif /* CONFIG_HAVE_ARCH_NODEDATA_EXTENSION */
 
-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);
 
diff --git a/mm/bootmem_info.c b/mm/bootmem_info.c
index 39fa8fc120bc..d276e96e487f 100644
--- a/mm/bootmem_info.c
+++ b/mm/bootmem_info.c
@@ -10,6 +10,32 @@
 #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)
 {
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 2da4ad071456..ae57eedc341f 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -21,7 +21,6 @@
 #include <linux/memory.h>
 #include <linux/memremap.h>
 #include <linux/memory_hotplug.h>
-#include <linux/bootmem_info.h>
 #include <linux/highmem.h>
 #include <linux/vmalloc.h>
 #include <linux/ioport.h>
@@ -142,32 +141,6 @@ 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);
-	}
-}
-
 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 b25ad8e64839..a4138410d890 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>
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 03/24] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 01/24] mm/memory_hotplug: Move bootmem info registration API to bootmem_info.c Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 02/24] mm/memory_hotplug: Move {get,put}_page_bootmem() " Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-16  2:13   ` Randy Dunlap
  2020-09-29 23:41   ` Mike Kravetz
  2020-09-15 12:59 ` [RFC PATCH 04/24] mm/hugetlb: Register bootmem info when CONFIG_HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
                   ` (22 subsequent siblings)
  25 siblings, 2 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

The purpose of introducing HUGETLB_PAGE_FREE_VMEMMAP is to configure
whether to enable the feature of freeing unused vmemmap associated
with HugeTLB pages.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 fs/Kconfig | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/fs/Kconfig b/fs/Kconfig
index 976e8b9033c4..61e9c08096ca 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -245,6 +245,21 @@ config HUGETLBFS
 config HUGETLB_PAGE
 	def_bool HUGETLBFS
 
+config HUGETLB_PAGE_FREE_VMEMMAP
+	bool "Free unused vmemmap associated with HugeTLB pages"
+	default n
+	depends on HUGETLB_PAGE
+	depends on SPARSEMEM_VMEMMAP
+	depends on HAVE_BOOTMEM_INFO_NODE
+	help
+	  There are many struct page structure associated with each HugeTLB
+	  page. But we only use a few struct page structure. In this case,
+	  it waste some memory. It is better to free the unused struct page
+	  structures to buddy system which can save some memory. For
+	  architectures that support it, say Y here.
+
+	  If unsure, say N.
+
 config MEMFD_CREATE
 	def_bool TMPFS || HUGETLBFS
 
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 04/24] mm/hugetlb: Register bootmem info when CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (2 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 03/24] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 05/24] mm/hugetlb: Introduce nr_free_vmemmap_pages in the struct hstate Muchun Song
                   ` (21 subsequent siblings)
  25 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

We use put_page_bootmem() to free the unused vmemmap pages associated with
each hugetlb page, so we need register bootmem info in advance, even if
!CONFIG_NUMA.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 arch/x86/mm/init_64.c | 2 +-
 1 file changed, 1 insertion(+), 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)
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 05/24] mm/hugetlb: Introduce nr_free_vmemmap_pages in the struct hstate
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (3 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 04/24] mm/hugetlb: Register bootmem info when CONFIG_HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-30 22:41   ` Mike Kravetz
  2020-09-15 12:59 ` [RFC PATCH 06/24] mm/hugetlb: Introduce pgtable allocation/freeing helpers Muchun Song
                   ` (20 subsequent siblings)
  25 siblings, 1 reply; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

If the size of hugetlb page is 2MB, we need 512 struct page structures
(8 pages) to be associated with it. As far as I know, we only use the
first 3 struct page structures and only read the compound_dtor members
of the remaining struct page structures. For tail page, the value of
compound_dtor is the same. So we can reuse first tail page. We map the
virtual addresses of the remaining 6 tail pages to the first tail page,
and then free these 6 pages. Therefore, we need to reserve at least 2
pages as vmemmap areas.

So we introduce a new nr_free_vmemmap_pages field in the hstate to
indicate how many vmemmap pages associated with a hugetlb page that we
can free to buddy system.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 include/linux/hugetlb.h |  3 +++
 mm/hugetlb.c            | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index d5cc5f802dd4..eed3dd3bd626 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -492,6 +492,9 @@ 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 81a41aa080a5..f1b2b733b49b 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1292,6 +1292,39 @@ static inline void destroy_compound_gigantic_page(struct page *page,
 						unsigned int order) { }
 #endif
 
+#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+#define RESERVE_VMEMMAP_NR	2U
+
+static inline unsigned int nr_free_vmemmap(struct hstate *h)
+{
+	return h->nr_free_vmemmap_pages;
+}
+
+static void __init hugetlb_vmemmap_init(struct hstate *h)
+{
+	unsigned int order = huge_page_order(h);
+	unsigned int vmemmap_pages;
+
+	vmemmap_pages = ((1 << order) * sizeof(struct page)) >> PAGE_SHIFT;
+	/*
+	 * The head page and the first tail page not free to buddy system,
+	 * the others page will map to the first tail page. So there are
+	 * (@vmemmap_pages - RESERVE_VMEMMAP_NR) pages can be freed.
+	 */
+	if (vmemmap_pages > RESERVE_VMEMMAP_NR)
+		h->nr_free_vmemmap_pages = vmemmap_pages - RESERVE_VMEMMAP_NR;
+	else
+		h->nr_free_vmemmap_pages = 0;
+
+	pr_info("HugeTLB: can free %d vmemmap pages for %s\n",
+		h->nr_free_vmemmap_pages, h->name);
+}
+#else
+static inline void hugetlb_vmemmap_init(struct hstate *h)
+{
+}
+#endif
+
 static void update_and_free_page(struct hstate *h, struct page *page)
 {
 	int i;
@@ -3285,6 +3318,8 @@ void __init hugetlb_add_hstate(unsigned int order)
 	snprintf(h->name, HSTATE_NAME_LEN, "hugepages-%lukB",
 					huge_page_size(h)/1024);
 
+	hugetlb_vmemmap_init(h);
+
 	parsed_hstate = h;
 }
 
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 06/24] mm/hugetlb: Introduce pgtable allocation/freeing helpers
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (4 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 05/24] mm/hugetlb: Introduce nr_free_vmemmap_pages in the struct hstate Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 07/24] mm/hugetlb: Add freeing unused vmemmap pages support for x86 Muchun Song
                   ` (19 subsequent siblings)
  25 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

On some architectures, the vmemmap areas use huge page mapping.
If we want to free the unused vmemmap pages, we have to split
the huge pmd firstly. So we should pre-allocate pgtable to split
huge pmd.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 include/linux/hugetlb.h |  17 ++++++
 mm/hugetlb.c            | 117 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 134 insertions(+)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index eed3dd3bd626..ace304a6196c 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -593,6 +593,23 @@ static inline unsigned int blocks_per_huge_page(struct hstate *h)
 
 #include <asm/hugetlb.h>
 
+#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+#ifndef arch_vmemmap_support_huge_mapping
+static inline bool arch_vmemmap_support_huge_mapping(void)
+{
+	return false;
+}
+#endif
+
+#ifndef VMEMMAP_HPAGE_SHIFT
+#define VMEMMAP_HPAGE_SHIFT		PMD_SHIFT
+#endif
+#define VMEMMAP_HPAGE_ORDER		(VMEMMAP_HPAGE_SHIFT - PAGE_SHIFT)
+#define VMEMMAP_HPAGE_NR		(1 << VMEMMAP_HPAGE_ORDER)
+#define VMEMMAP_HPAGE_SIZE		((1UL) << VMEMMAP_HPAGE_SHIFT)
+#define VMEMMAP_HPAGE_MASK		(~(VMEMMAP_HPAGE_SIZE - 1))
+#endif /* CONFIG_HUGETLB_PAGE_FREE_VMEMMAP */
+
 #ifndef is_hugepage_only_range
 static inline int is_hugepage_only_range(struct mm_struct *mm,
 					unsigned long addr, unsigned long len)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index f1b2b733b49b..d6ae9b6876be 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1295,11 +1295,108 @@ static inline void destroy_compound_gigantic_page(struct page *page,
 #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
 #define RESERVE_VMEMMAP_NR	2U
 
+#define page_huge_pte(page)	((page)->pmd_huge_pte)
+
 static inline unsigned int nr_free_vmemmap(struct hstate *h)
 {
 	return h->nr_free_vmemmap_pages;
 }
 
+static inline unsigned int nr_vmemmap(struct hstate *h)
+{
+	return nr_free_vmemmap(h) + RESERVE_VMEMMAP_NR;
+}
+
+static inline unsigned long nr_vmemmap_size(struct hstate *h)
+{
+	return (unsigned long)nr_vmemmap(h) << PAGE_SHIFT;
+}
+
+static inline unsigned int nr_pgtable(struct hstate *h)
+{
+	unsigned long vmemmap_size = nr_vmemmap_size(h);
+
+	if (!arch_vmemmap_support_huge_mapping())
+		return 0;
+
+	/*
+	 * No need pre-allocate page tabels when there is no vmemmap pages
+	 * to free.
+	 */
+	if (!nr_free_vmemmap(h))
+		return 0;
+
+	return ALIGN(vmemmap_size, VMEMMAP_HPAGE_SIZE) >> VMEMMAP_HPAGE_SHIFT;
+}
+
+static inline void vmemmap_pgtable_init(struct page *page)
+{
+	page_huge_pte(page) = NULL;
+}
+
+static void vmemmap_pgtable_deposit(struct page *page, pte_t *pte_p)
+{
+	pgtable_t pgtable = virt_to_page(pte_p);
+
+	/* FIFO */
+	if (!page_huge_pte(page))
+		INIT_LIST_HEAD(&pgtable->lru);
+	else
+		list_add(&pgtable->lru, &page_huge_pte(page)->lru);
+	page_huge_pte(page) = pgtable;
+}
+
+static pte_t *vmemmap_pgtable_withdraw(struct page *page)
+{
+	pgtable_t pgtable;
+
+	/* FIFO */
+	pgtable = page_huge_pte(page);
+	if (unlikely(!pgtable))
+		return NULL;
+	page_huge_pte(page) = list_first_entry_or_null(&pgtable->lru,
+						       struct page, lru);
+	if (page_huge_pte(page))
+		list_del(&pgtable->lru);
+	return page_to_virt(pgtable);
+}
+
+static int vmemmap_pgtable_prealloc(struct hstate *h, struct page *page)
+{
+	int i;
+	pte_t *pte_p;
+	unsigned int nr = nr_pgtable(h);
+
+	if (!nr)
+		return 0;
+
+	vmemmap_pgtable_init(page);
+
+	for (i = 0; i < nr; i++) {
+		pte_p = pte_alloc_one_kernel(&init_mm);
+		if (!pte_p)
+			goto out;
+		vmemmap_pgtable_deposit(page, pte_p);
+	}
+
+	return 0;
+out:
+	while (i-- && (pte_p = vmemmap_pgtable_withdraw(page)))
+		pte_free_kernel(&init_mm, pte_p);
+	return -ENOMEM;
+}
+
+static inline void vmemmap_pgtable_free(struct hstate *h, struct page *page)
+{
+	pte_t *pte_p;
+
+	if (!nr_pgtable(h))
+		return;
+
+	while ((pte_p = vmemmap_pgtable_withdraw(page)))
+		pte_free_kernel(&init_mm, pte_p);
+}
+
 static void __init hugetlb_vmemmap_init(struct hstate *h)
 {
 	unsigned int order = huge_page_order(h);
@@ -1323,6 +1420,15 @@ static void __init hugetlb_vmemmap_init(struct hstate *h)
 static inline void hugetlb_vmemmap_init(struct hstate *h)
 {
 }
+
+static inline int vmemmap_pgtable_prealloc(struct hstate *h, struct page *page)
+{
+	return 0;
+}
+
+static inline void vmemmap_pgtable_free(struct hstate *h, struct page *page)
+{
+}
 #endif
 
 static void update_and_free_page(struct hstate *h, struct page *page)
@@ -1531,6 +1637,9 @@ void free_huge_page(struct page *page)
 
 static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
 {
+	/* Must be called before the initialization of @page->lru */
+	vmemmap_pgtable_free(h, page);
+
 	INIT_LIST_HEAD(&page->lru);
 	set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
 	set_hugetlb_cgroup(page, NULL);
@@ -1783,6 +1892,14 @@ static struct page *alloc_fresh_huge_page(struct hstate *h,
 	if (!page)
 		return NULL;
 
+	if (vmemmap_pgtable_prealloc(h, page)) {
+		if (hstate_is_gigantic(h))
+			free_gigantic_page(page, huge_page_order(h));
+		else
+			put_page(page);
+		return NULL;
+	}
+
 	if (hstate_is_gigantic(h))
 		prep_compound_gigantic_page(page, huge_page_order(h));
 	prep_new_huge_page(h, page, page_to_nid(page));
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 07/24] mm/hugetlb: Add freeing unused vmemmap pages support for x86
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (5 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 06/24] mm/hugetlb: Introduce pgtable allocation/freeing helpers Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 08/24] mm/bootmem_info: Introduce {free,prepare}_vmemmap_page() Muchun Song
                   ` (18 subsequent siblings)
  25 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

On x86_64 architecture, we use hupe page mapping vmemmap area. We
should define VMEMMAP_HPAGE_SHIFT to the correct value to support
freeing unused vmemmap pages.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 arch/x86/include/asm/hugetlb.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/include/asm/hugetlb.h b/arch/x86/include/asm/hugetlb.h
index 1721b1aadeb1..f5e882f999cd 100644
--- a/arch/x86/include/asm/hugetlb.h
+++ b/arch/x86/include/asm/hugetlb.h
@@ -5,6 +5,11 @@
 #include <asm/page.h>
 #include <asm-generic/hugetlb.h>
 
+#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+#define VMEMMAP_HPAGE_SHIFT			PMD_SHIFT
+#define arch_vmemmap_support_huge_mapping()	boot_cpu_has(X86_FEATURE_PSE)
+#endif
+
 #define hugepages_supported() boot_cpu_has(X86_FEATURE_PSE)
 
 #endif /* _ASM_X86_HUGETLB_H */
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 08/24] mm/bootmem_info: Introduce {free,prepare}_vmemmap_page()
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (6 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 07/24] mm/hugetlb: Add freeing unused vmemmap pages support for x86 Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 09/24] x86/mm: Introduce VMEMMAP_SIZE/VMEMMAP_END macro Muchun Song
                   ` (17 subsequent siblings)
  25 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

In the later patch, we can use the free_vmemmap_page() to free the
unused vmemmap pages and initialize a page for vmemmap page using
via prepare_vmemmap_page().

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 include/linux/bootmem_info.h | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/include/linux/bootmem_info.h b/include/linux/bootmem_info.h
index 4ed6dee1adc9..ce9d8c97369d 100644
--- a/include/linux/bootmem_info.h
+++ b/include/linux/bootmem_info.h
@@ -3,6 +3,7 @@
 #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 +23,30 @@ 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);
+
+static inline void free_vmemmap_page(struct page *page)
+{
+	VM_WARN_ON(!PageReserved(page) || page_ref_count(page) != 2);
+
+	/* bootmem page has reserved flag in the reserve_bootmem_region */
+	if (PageReserved(page)) {
+		unsigned long magic = (unsigned long)page->freelist;
+
+		if (magic == SECTION_INFO || magic == MIX_SECTION_INFO)
+			put_page_bootmem(page);
+		else
+			WARN_ON(1);
+	}
+}
+
+static inline void prepare_vmemmap_page(struct page *page)
+{
+	unsigned long section_nr = pfn_to_section_nr(page_to_pfn(page));
+
+	get_page_bootmem(section_nr, page, SECTION_INFO);
+	__SetPageReserved(page);
+	adjust_managed_page_count(page, -1);
+}
 #else
 static inline void register_page_bootmem_info_node(struct pglist_data *pgdat)
 {
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 09/24] x86/mm: Introduce VMEMMAP_SIZE/VMEMMAP_END macro
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (7 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 08/24] mm/bootmem_info: Introduce {free,prepare}_vmemmap_page() Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 10/24] mm/hugetlb: Free the vmemmap pages associated with each hugetlb page Muchun Song
                   ` (16 subsequent siblings)
  25 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

In the later patch, we will walk the page table for vmemmap area.
So we want to know the range of vmemmap area addresses in order to
distinguish whether it comes from vememmap areas. If not, just we
can do not walk the page table.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 arch/x86/include/asm/pgtable_64_types.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
index 52e5f5f2240d..bedbd2e7d06c 100644
--- a/arch/x86/include/asm/pgtable_64_types.h
+++ b/arch/x86/include/asm/pgtable_64_types.h
@@ -139,6 +139,14 @@ extern unsigned int ptrs_per_p4d;
 # define VMEMMAP_START		__VMEMMAP_BASE_L4
 #endif /* CONFIG_DYNAMIC_MEMORY_LAYOUT */
 
+/*
+ * VMEMMAP_SIZE - allows the whole linear region to be covered by
+ *                a struct page array.
+ */
+#define VMEMMAP_SIZE		(1UL << (__VIRTUAL_MASK_SHIFT - PAGE_SHIFT - \
+					 1 + ilog2(sizeof(struct page))))
+#define VMEMMAP_END		(VMEMMAP_START + VMEMMAP_SIZE)
+
 #define VMALLOC_END		(VMALLOC_START + (VMALLOC_SIZE_TB << 40) - 1)
 
 #define MODULES_VADDR		(__START_KERNEL_map + KERNEL_IMAGE_SIZE)
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 10/24] mm/hugetlb: Free the vmemmap pages associated with each hugetlb page
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (8 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 09/24] x86/mm: Introduce VMEMMAP_SIZE/VMEMMAP_END macro Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 11/24] mm/hugetlb: Add vmemmap_pmd_huge macro for x86 Muchun Song
                   ` (15 subsequent siblings)
  25 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

When we allocate a hugetlb page from the buddy, we should free the
unused vmemmap pages associated with it. We can do that in the
prep_new_huge_page().

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 include/linux/hugetlb.h |  21 ++++
 mm/hugetlb.c            | 231 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 252 insertions(+)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index ace304a6196c..2561af2ad901 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -601,6 +601,13 @@ static inline bool arch_vmemmap_support_huge_mapping(void)
 }
 #endif
 
+#ifndef vmemmap_pmd_huge
+static inline bool vmemmap_pmd_huge(pmd_t *pmd)
+{
+	return pmd_huge(*pmd);
+}
+#endif
+
 #ifndef VMEMMAP_HPAGE_SHIFT
 #define VMEMMAP_HPAGE_SHIFT		PMD_SHIFT
 #endif
@@ -790,6 +797,15 @@ static inline void huge_ptep_modify_prot_commit(struct vm_area_struct *vma,
 }
 #endif
 
+#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+int handle_vmemmap_fault(unsigned long page);
+#else
+static inline int handle_vmemmap_fault(unsigned long page)
+{
+	return -EFAULT;
+}
+#endif
+
 #else	/* CONFIG_HUGETLB_PAGE */
 struct hstate {};
 
@@ -943,6 +959,11 @@ 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 int handle_vmemmap_fault(unsigned long page)
+{
+	return -EFAULT;
+}
 #endif	/* CONFIG_HUGETLB_PAGE */
 
 static inline spinlock_t *huge_pte_lock(struct hstate *h,
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index d6ae9b6876be..a628588a075a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1293,10 +1293,20 @@ static inline void destroy_compound_gigantic_page(struct page *page,
 #endif
 
 #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+#include <linux/bootmem_info.h>
+
 #define RESERVE_VMEMMAP_NR	2U
+#define RESERVE_VMEMMAP_SIZE	(RESERVE_VMEMMAP_NR << PAGE_SHIFT)
 
 #define page_huge_pte(page)	((page)->pmd_huge_pte)
 
+#define vmemmap_hpage_addr_end(addr, end)				\
+({									\
+	unsigned long __boundary;					\
+	__boundary = ((addr) + VMEMMAP_HPAGE_SIZE) & VMEMMAP_HPAGE_MASK;\
+	(__boundary - 1 < (end) - 1) ? __boundary : (end);		\
+})
+
 static inline unsigned int nr_free_vmemmap(struct hstate *h)
 {
 	return h->nr_free_vmemmap_pages;
@@ -1416,6 +1426,222 @@ static void __init hugetlb_vmemmap_init(struct hstate *h)
 	pr_info("HugeTLB: can free %d vmemmap pages for %s\n",
 		h->nr_free_vmemmap_pages, h->name);
 }
+
+static inline spinlock_t *vmemmap_pmd_lockptr(pmd_t *pmd)
+{
+	static DEFINE_SPINLOCK(pgtable_lock);
+
+	return &pgtable_lock;
+}
+
+/*
+ * Walk a vmemmap address to the pmd it maps.
+ */
+static pmd_t *vmemmap_to_pmd(const void *page)
+{
+	unsigned long addr = (unsigned long)page;
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+
+	if (addr < VMEMMAP_START || addr >= VMEMMAP_END)
+		return NULL;
+
+	pgd = pgd_offset_k(addr);
+	if (pgd_none(*pgd))
+		return NULL;
+	p4d = p4d_offset(pgd, addr);
+	if (p4d_none(*p4d))
+		return NULL;
+	pud = pud_offset(p4d, addr);
+
+	WARN_ON_ONCE(pud_bad(*pud));
+	if (pud_none(*pud) || pud_bad(*pud))
+		return NULL;
+	pmd = pmd_offset(pud, addr);
+
+	return pmd;
+}
+
+static inline int freed_vmemmap_hpage(struct page *page)
+{
+	return atomic_read(&page->_mapcount) + 1;
+}
+
+static inline int freed_vmemmap_hpage_inc(struct page *page)
+{
+	return atomic_inc_return_relaxed(&page->_mapcount) + 1;
+}
+
+static inline int freed_vmemmap_hpage_dec(struct page *page)
+{
+	return atomic_dec_return_relaxed(&page->_mapcount) + 1;
+}
+
+static inline 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 __free_huge_page_pte_vmemmap(struct page *reuse, pte_t *ptep,
+					 unsigned long start,
+					 unsigned int nr_free,
+					 struct list_head *free_pages)
+{
+	pte_t entry = mk_pte(reuse, PAGE_KERNEL);
+	unsigned long addr;
+	unsigned long end = start + (nr_free  << PAGE_SHIFT);
+
+	for (addr = start; addr < end; addr += PAGE_SIZE, ptep++) {
+		struct page *page;
+		pte_t old = *ptep;
+
+		VM_WARN_ON(!pte_present(old));
+		page = pte_page(old);
+		list_add(&page->lru, free_pages);
+
+		set_pte_at(&init_mm, addr, ptep, entry);
+	}
+}
+
+static void __free_huge_page_pmd_vmemmap(struct hstate *h, pmd_t *pmd,
+					 unsigned long addr,
+					 struct list_head *free_pages)
+{
+	unsigned long next;
+	unsigned long start = addr + RESERVE_VMEMMAP_NR * PAGE_SIZE;
+	unsigned long end = addr + nr_vmemmap_size(h);
+	struct page *reuse = NULL;
+
+	addr = start;
+	do {
+		unsigned int nr_pages;
+		pte_t *ptep;
+
+		ptep = pte_offset_kernel(pmd, addr);
+		if (!reuse)
+			reuse = pte_page(ptep[-1]);
+
+		next = vmemmap_hpage_addr_end(addr, end);
+		nr_pages = (next - addr) >> PAGE_SHIFT;
+		__free_huge_page_pte_vmemmap(reuse, ptep, addr, nr_pages,
+					     free_pages);
+	} while (pmd++, addr = next, addr != end);
+
+	flush_tlb_kernel_range(start, end);
+}
+
+static void split_vmemmap_pmd(pmd_t *pmd, pte_t *pte_p, unsigned long addr)
+{
+	struct mm_struct *mm = &init_mm;
+	struct page *page;
+	pmd_t old_pmd, _pmd;
+	int i;
+
+	/*
+	 * Up to this point the pmd is present and huge and userland has the
+	 * whole access to the hugepage during the split (which happens in
+	 * place). If we overwrite the pmd with the not-huge version pointing
+	 * to the pte here (which of course we could if all CPUs were bug
+	 * free), userland could trigger a small page size TLB miss on the
+	 * small sized TLB while the hugepage TLB entry is still established in
+	 * the huge TLB. Some CPU doesn't like that.
+	 *
+	 * See http://support.amd.com/us/Processor_TechDocs/41322.pdf, Erratum
+	 * 383 on page 93. Intel should be safe but is also warns that it's
+	 * only safe if the permission and cache attributes of the two entries
+	 * loaded in the two TLB is identical (which should be the case here).
+	 *
+	 * So it is generally safer to never allow small and huge TLB entries
+	 * for the same virtual address to be loaded simultaneously. But here
+	 * we should not set pmd non-present first and flush TLB. Because if
+	 * we do that(maybe trriger IPI to other CPUs to flush TLB), we may be
+	 * deadlocked. So we have to break the above rules. Be careful, Let us
+	 * suppose all CPUs are bug free, otherwise, we should not enable the
+	 * feature of freeing unused vmemmap pages on the bug CPU.
+	 *
+	 * Why we should not set pmd non-present first? Here we already hold
+	 * the vmemmap pgtable spinlock on CPU1 and set pmd non-present. If
+	 * CPU0 access the struct page with irqs disabled and the vmemmap
+	 * pgtable lock is held by CPU1. In this case, the CPU0 can not handle
+	 * the IPI interrupt to flush TLB because of the disabling of irqs.
+	 * Then we can deadlock. In order to avoid this issue, we do not set
+	 * pmd non-present.
+	 *
+	 * The deadlock scene is shown below.
+	 *
+	 *     CPU0:                                        CPU1:
+	 * disable irqs                           hold the vmemmap pgtable lock
+	 *                                        set pmd non-present
+	 * read/write `struct page`(page fault)
+	 * jump to handle_vmemmap_fault
+	 * spin for vmemmap pgtable lock
+	 *                                        flush_tlb(send IPI to CPU0)
+	 *                                        set new pmd(small page)
+	 */
+	old_pmd = READ_ONCE(*pmd);
+	page = pmd_page(old_pmd);
+	pmd_populate_kernel(mm, &_pmd, pte_p);
+
+	for (i = 0; i < VMEMMAP_HPAGE_NR; i++, addr += PAGE_SIZE) {
+		pte_t entry, *pte;
+
+		entry = mk_pte(page + i, PAGE_KERNEL);
+		pte = pte_offset_kernel(&_pmd, addr);
+		VM_BUG_ON(!pte_none(*pte));
+		set_pte_at(mm, addr, pte, entry);
+	}
+
+	/* make pte visible before pmd */
+	smp_wmb();
+	pmd_populate_kernel(mm, pmd, pte_p);
+}
+
+static void split_vmemmap_huge_page(struct page *head, pmd_t *pmd)
+{
+	pte_t *pte_p;
+	unsigned long start = (unsigned long)head & VMEMMAP_HPAGE_MASK;
+	unsigned long addr = start;
+
+	while ((pte_p = vmemmap_pgtable_withdraw(head))) {
+		VM_BUG_ON(freed_vmemmap_hpage(virt_to_page(pte_p)));
+		split_vmemmap_pmd(pmd++, pte_p, addr);
+		addr += VMEMMAP_HPAGE_SIZE;
+	}
+
+	flush_tlb_kernel_range(start, addr);
+}
+
+static void free_huge_page_vmemmap(struct hstate *h, struct page *head)
+{
+	pmd_t *pmd;
+	spinlock_t *ptl;
+	LIST_HEAD(free_pages);
+
+	if (!nr_free_vmemmap(h))
+		return;
+
+	pmd = vmemmap_to_pmd(head);
+	ptl = vmemmap_pmd_lockptr(pmd);
+
+	spin_lock(ptl);
+	if (vmemmap_pmd_huge(pmd)) {
+		VM_BUG_ON(!nr_pgtable(h));
+		split_vmemmap_huge_page(head, pmd);
+	}
+
+	__free_huge_page_pmd_vmemmap(h, pmd, (unsigned long)head, &free_pages);
+	freed_vmemmap_hpage_inc(pmd_page(*pmd));
+	spin_unlock(ptl);
+
+	free_vmemmap_page_list(&free_pages);
+}
 #else
 static inline void hugetlb_vmemmap_init(struct hstate *h)
 {
@@ -1429,6 +1655,10 @@ static inline int vmemmap_pgtable_prealloc(struct hstate *h, struct page *page)
 static inline void vmemmap_pgtable_free(struct hstate *h, struct page *page)
 {
 }
+
+static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head)
+{
+}
 #endif
 
 static void update_and_free_page(struct hstate *h, struct page *page)
@@ -1637,6 +1867,7 @@ void free_huge_page(struct page *page)
 
 static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
 {
+	free_huge_page_vmemmap(h, page);
 	/* Must be called before the initialization of @page->lru */
 	vmemmap_pgtable_free(h, page);
 
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 11/24] mm/hugetlb: Add vmemmap_pmd_huge macro for x86
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (9 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 10/24] mm/hugetlb: Free the vmemmap pages associated with each hugetlb page Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 12/24] mm/hugetlb: Defer freeing of hugetlb pages Muchun Song
                   ` (14 subsequent siblings)
  25 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

Use pmd_large instead of pmd_huge on x86, so we implement the
vmemmap_pmd_huge macro.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 arch/x86/include/asm/hugetlb.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/include/asm/hugetlb.h b/arch/x86/include/asm/hugetlb.h
index f5e882f999cd..7c3eb60c2198 100644
--- a/arch/x86/include/asm/hugetlb.h
+++ b/arch/x86/include/asm/hugetlb.h
@@ -4,10 +4,17 @@
 
 #include <asm/page.h>
 #include <asm-generic/hugetlb.h>
+#include <asm/pgtable.h>
 
 #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
 #define VMEMMAP_HPAGE_SHIFT			PMD_SHIFT
 #define arch_vmemmap_support_huge_mapping()	boot_cpu_has(X86_FEATURE_PSE)
+
+#define vmemmap_pmd_huge vmemmap_pmd_huge
+static inline bool vmemmap_pmd_huge(pmd_t *pmd)
+{
+	return pmd_large(*pmd);
+}
 #endif
 
 #define hugepages_supported() boot_cpu_has(X86_FEATURE_PSE)
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 12/24] mm/hugetlb: Defer freeing of hugetlb pages
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (10 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 11/24] mm/hugetlb: Add vmemmap_pmd_huge macro for x86 Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 13/24] mm/hugetlb: Allocate the vmemmap pages associated with each hugetlb page Muchun Song
                   ` (13 subsequent siblings)
  25 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

In the subsequent patch, we will allocate the vmemmap pages when free
huge pages. But update_and_free_page() is be called from a non-task
context(and hold hugetlb_lock), we can defer the actual freeing in
a workqueue to prevent use GFP_ATOMIC to allocate the vmemmap pages.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/hugetlb.c | 94 +++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 85 insertions(+), 9 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index a628588a075a..6b57a1183785 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1292,6 +1292,8 @@ static inline void destroy_compound_gigantic_page(struct page *page,
 						unsigned int order) { }
 #endif
 
+static void __free_hugepage(struct hstate *h, struct page *page);
+
 #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
 #include <linux/bootmem_info.h>
 
@@ -1642,6 +1644,64 @@ static void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 
 	free_vmemmap_page_list(&free_pages);
 }
+
+/*
+ * As update_and_free_page() is be called from a non-task context(and hold
+ * hugetlb_lock), we can defer the actual freeing in a workqueue to prevent
+ * use GFP_ATOMIC to allocate a lot of vmemmap pages.
+ *
+ * update_hpage_vmemmap_workfn() locklessly retrieves the linked list of
+ * pages to be freed and frees them one-by-one. As the page->mapping pointer
+ * is going to be cleared in update_hpage_vmemmap_workfn() anyway, it is
+ * reused as the llist_node structure of a lockless linked list of huge
+ * pages to be freed.
+ */
+static LLIST_HEAD(hpage_update_freelist);
+
+static void update_hpage_vmemmap_workfn(struct work_struct *work)
+{
+	struct llist_node *node;
+	struct page *page;
+
+	node = llist_del_all(&hpage_update_freelist);
+
+	while (node) {
+		page = container_of((struct address_space **)node,
+				     struct page, mapping);
+		node = node->next;
+		page->mapping = NULL;
+		__free_hugepage(page_hstate(page), page);
+
+		cond_resched();
+	}
+}
+static DECLARE_WORK(hpage_update_work, update_hpage_vmemmap_workfn);
+
+static inline void __update_and_free_page(struct hstate *h, struct page *page)
+{
+	/* No need to allocate vmemmap pages */
+	if (!nr_free_vmemmap(h)) {
+		__free_hugepage(h, page);
+		return;
+	}
+
+	/*
+	 * Defer freeing to avoid using GFP_ATOMIC to allocate vmemmap
+	 * pages.
+	 *
+	 * Only call schedule_work() if hpage_update_freelist is previously
+	 * empty. Otherwise, schedule_work() had been called but the workfn
+	 * hasn't retrieved the list yet.
+	 */
+	if (llist_add((struct llist_node *)&page->mapping,
+		      &hpage_update_freelist))
+		schedule_work(&hpage_update_work);
+}
+
+static inline void free_gigantic_page_comm(struct hstate *h, struct page *page)
+{
+	free_gigantic_page(page, huge_page_order(h));
+}
 #else
 static inline void hugetlb_vmemmap_init(struct hstate *h)
 {
@@ -1659,17 +1719,39 @@ static inline void vmemmap_pgtable_free(struct hstate *h, struct page *page)
 static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 {
 }
+
+static inline void __update_and_free_page(struct hstate *h, struct page *page)
+{
+	__free_hugepage(h, page);
+}
+
+static inline void free_gigantic_page_comm(struct hstate *h, struct page *page)
+{
+	/*
+	 * Temporarily drop the hugetlb_lock, because
+	 * we might block in free_gigantic_page().
+	 */
+	spin_unlock(&hugetlb_lock);
+	free_gigantic_page(page, huge_page_order(h));
+	spin_lock(&hugetlb_lock);
+}
 #endif
 
 static void update_and_free_page(struct hstate *h, struct page *page)
 {
-	int i;
-
 	if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
 		return;
 
 	h->nr_huge_pages--;
 	h->nr_huge_pages_node[page_to_nid(page)]--;
+
+	__update_and_free_page(h, page);
+}
+
+static void __free_hugepage(struct hstate *h, struct page *page)
+{
+	int i;
+
 	for (i = 0; i < pages_per_huge_page(h); i++) {
 		page[i].flags &= ~(1 << PG_locked | 1 << PG_error |
 				1 << PG_referenced | 1 << PG_dirty |
@@ -1681,14 +1763,8 @@ static void update_and_free_page(struct hstate *h, struct page *page)
 	set_compound_page_dtor(page, NULL_COMPOUND_DTOR);
 	set_page_refcounted(page);
 	if (hstate_is_gigantic(h)) {
-		/*
-		 * Temporarily drop the hugetlb_lock, because
-		 * we might block in free_gigantic_page().
-		 */
-		spin_unlock(&hugetlb_lock);
 		destroy_compound_gigantic_page(page, huge_page_order(h));
-		free_gigantic_page(page, huge_page_order(h));
-		spin_lock(&hugetlb_lock);
+		free_gigantic_page_comm(h, page);
 	} else {
 		__free_pages(page, huge_page_order(h));
 	}
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 13/24] mm/hugetlb: Allocate the vmemmap pages associated with each hugetlb page
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (11 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 12/24] mm/hugetlb: Defer freeing of hugetlb pages Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 14/24] mm/hugetlb: Introduce remap_huge_page_pmd_vmemmap helper Muchun Song
                   ` (12 subsequent siblings)
  25 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

When we free a hugetlb page to the buddy, we should allocate the vmemmap
pages associated with it. We can do that in the __free_hugepage().

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/hugetlb.c | 108 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 108 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 6b57a1183785..d0f09fe531fc 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1299,6 +1299,7 @@ static void __free_hugepage(struct hstate *h, struct page *page);
 
 #define RESERVE_VMEMMAP_NR	2U
 #define RESERVE_VMEMMAP_SIZE	(RESERVE_VMEMMAP_NR << PAGE_SHIFT)
+#define GFP_VMEMMAP_PAGE	(GFP_KERNEL | __GFP_NOFAIL | __GFP_MEMALLOC)
 
 #define page_huge_pte(page)	((page)->pmd_huge_pte)
 
@@ -1645,6 +1646,107 @@ static void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 	free_vmemmap_page_list(&free_pages);
 }
 
+static void __remap_huge_page_pte_vmemmap(struct page *reuse, pte_t *ptep,
+					  unsigned long start,
+					  unsigned int nr_remap,
+					  struct list_head *remap_pages)
+{
+	void *from = (void *)page_private(reuse);
+	unsigned long addr, end = start + (nr_remap << PAGE_SHIFT);
+
+	for (addr = start; addr < end; addr += PAGE_SIZE) {
+		void *to;
+		struct page *page;
+		pte_t entry, old = *ptep;
+
+		page = list_first_entry_or_null(remap_pages, struct page, lru);
+		list_del(&page->lru);
+		to = page_to_virt(page);
+		copy_page(to, from);
+
+		/*
+		 * Make sure that any data that writes to the @to is made
+		 * visible to the physical page.
+		 */
+		flush_kernel_vmap_range(to, PAGE_SIZE);
+
+		prepare_vmemmap_page(page);
+
+		entry = mk_pte(page, PAGE_KERNEL);
+		set_pte_at(&init_mm, addr, ptep++, entry);
+
+		VM_BUG_ON(!pte_present(old) || pte_page(old) != reuse);
+	}
+}
+
+static void __remap_huge_page_pmd_vmemmap(struct hstate *h, pmd_t *pmd,
+					  unsigned long addr,
+					  struct list_head *remap_pages)
+{
+	unsigned long next;
+	unsigned long start = addr + RESERVE_VMEMMAP_NR * PAGE_SIZE;
+	unsigned long end = addr + nr_vmemmap_size(h);
+	struct page *reuse = NULL;
+
+	addr = start;
+	do {
+		unsigned int nr_pages;
+		pte_t *ptep;
+
+		ptep = pte_offset_kernel(pmd, addr);
+		if (!reuse) {
+			reuse = pte_page(ptep[-1]);
+			set_page_private(reuse, addr - PAGE_SIZE);
+		}
+
+		next = vmemmap_hpage_addr_end(addr, end);
+		nr_pages = (next - addr) >> PAGE_SHIFT;
+		__remap_huge_page_pte_vmemmap(reuse, ptep, addr, nr_pages,
+					      remap_pages);
+	} while (pmd++, addr = next, addr != end);
+
+	flush_tlb_kernel_range(start, end);
+}
+
+static inline void alloc_vmemmap_pages(struct hstate *h, struct list_head *list)
+{
+	int i;
+
+	for (i = 0; i < nr_free_vmemmap(h); i++) {
+		struct page *page;
+
+		/* This should not fail */
+		page = alloc_page(GFP_VMEMMAP_PAGE);
+		list_add_tail(&page->lru, list);
+	}
+}
+
+static void alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
+{
+	pmd_t *pmd;
+	spinlock_t *ptl;
+	LIST_HEAD(remap_pages);
+
+	if (!nr_free_vmemmap(h))
+		return;
+
+	alloc_vmemmap_pages(h, &remap_pages);
+
+	pmd = vmemmap_to_pmd(head);
+	ptl = vmemmap_pmd_lockptr(pmd);
+
+	spin_lock(ptl);
+	__remap_huge_page_pmd_vmemmap(h, pmd, (unsigned long)head,
+				      &remap_pages);
+	if (!freed_vmemmap_hpage_dec(pmd_page(*pmd))) {
+		/*
+		 * Todo:
+		 * Merge pte to huge pmd if it has ever been split.
+		 */
+	}
+	spin_unlock(ptl);
+}
+
 /*
  * As update_and_free_page() is be called from a non-task context(and hold
  * hugetlb_lock), we can defer the actual freeing in a workqueue to prevent
@@ -1720,6 +1822,10 @@ static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 {
 }
 
+static inline void alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
+{
+}
+
 static inline void __update_and_free_page(struct hstate *h, struct page *page)
 {
 	__free_hugepage(h, page);
@@ -1752,6 +1858,8 @@ static void __free_hugepage(struct hstate *h, struct page *page)
 {
 	int i;
 
+	alloc_huge_page_vmemmap(h, page);
+
 	for (i = 0; i < pages_per_huge_page(h); i++) {
 		page[i].flags &= ~(1 << PG_locked | 1 << PG_error |
 				1 << PG_referenced | 1 << PG_dirty |
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 14/24] mm/hugetlb: Introduce remap_huge_page_pmd_vmemmap helper
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (12 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 13/24] mm/hugetlb: Allocate the vmemmap pages associated with each hugetlb page Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 15/24] mm/hugetlb: Use PG_slab to indicate split pmd Muchun Song
                   ` (11 subsequent siblings)
  25 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

The __free_huge_page_pmd_vmemmap and __remap_huge_page_pmd_vmemmap are
almost the same code. So introduce remap_free_huge_page_pmd_vmemmap
helper to simplify the code.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/hugetlb.c | 98 +++++++++++++++++++++-------------------------------
 1 file changed, 39 insertions(+), 59 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index d0f09fe531fc..5cc796dc3a0a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1482,6 +1482,41 @@ static inline int freed_vmemmap_hpage_dec(struct page *page)
 	return atomic_dec_return_relaxed(&page->_mapcount) + 1;
 }
 
+typedef void (*remap_pte_fn)(struct page *reuse, pte_t *ptep,
+			     unsigned long start, unsigned int nr_pages,
+			     struct list_head *pages);
+
+static void remap_huge_page_pmd_vmemmap(struct hstate *h, pmd_t *pmd,
+					unsigned long addr,
+					struct list_head *pages,
+					remap_pte_fn remap_fn)
+{
+	unsigned long next;
+	unsigned long start = addr + RESERVE_VMEMMAP_SIZE;
+	unsigned long end = addr + nr_vmemmap_size(h);
+	struct page *reuse = NULL;
+
+	flush_cache_vunmap(start, end);
+
+	addr = start;
+	do {
+		unsigned int nr_pages;
+		pte_t *ptep;
+
+		ptep = pte_offset_kernel(pmd, addr);
+		if (!reuse) {
+			reuse = pte_page(ptep[-1]);
+			set_page_private(reuse, addr - PAGE_SIZE);
+		}
+
+		next = vmemmap_hpage_addr_end(addr, end);
+		nr_pages = (next - addr) >> PAGE_SHIFT;
+		remap_fn(reuse, ptep, addr, nr_pages, pages);
+	} while (pmd++, addr = next, addr != end);
+
+	flush_tlb_kernel_range(start, end);
+}
+
 static inline void free_vmemmap_page_list(struct list_head *list)
 {
 	struct page *page, *next;
@@ -1513,33 +1548,6 @@ static void __free_huge_page_pte_vmemmap(struct page *reuse, pte_t *ptep,
 	}
 }
 
-static void __free_huge_page_pmd_vmemmap(struct hstate *h, pmd_t *pmd,
-					 unsigned long addr,
-					 struct list_head *free_pages)
-{
-	unsigned long next;
-	unsigned long start = addr + RESERVE_VMEMMAP_NR * PAGE_SIZE;
-	unsigned long end = addr + nr_vmemmap_size(h);
-	struct page *reuse = NULL;
-
-	addr = start;
-	do {
-		unsigned int nr_pages;
-		pte_t *ptep;
-
-		ptep = pte_offset_kernel(pmd, addr);
-		if (!reuse)
-			reuse = pte_page(ptep[-1]);
-
-		next = vmemmap_hpage_addr_end(addr, end);
-		nr_pages = (next - addr) >> PAGE_SHIFT;
-		__free_huge_page_pte_vmemmap(reuse, ptep, addr, nr_pages,
-					     free_pages);
-	} while (pmd++, addr = next, addr != end);
-
-	flush_tlb_kernel_range(start, end);
-}
-
 static void split_vmemmap_pmd(pmd_t *pmd, pte_t *pte_p, unsigned long addr)
 {
 	struct mm_struct *mm = &init_mm;
@@ -1639,7 +1647,8 @@ static void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 		split_vmemmap_huge_page(head, pmd);
 	}
 
-	__free_huge_page_pmd_vmemmap(h, pmd, (unsigned long)head, &free_pages);
+	remap_huge_page_pmd_vmemmap(h, pmd, (unsigned long)head, &free_pages,
+				    __free_huge_page_pte_vmemmap);
 	freed_vmemmap_hpage_inc(pmd_page(*pmd));
 	spin_unlock(ptl);
 
@@ -1679,35 +1688,6 @@ static void __remap_huge_page_pte_vmemmap(struct page *reuse, pte_t *ptep,
 	}
 }
 
-static void __remap_huge_page_pmd_vmemmap(struct hstate *h, pmd_t *pmd,
-					  unsigned long addr,
-					  struct list_head *remap_pages)
-{
-	unsigned long next;
-	unsigned long start = addr + RESERVE_VMEMMAP_NR * PAGE_SIZE;
-	unsigned long end = addr + nr_vmemmap_size(h);
-	struct page *reuse = NULL;
-
-	addr = start;
-	do {
-		unsigned int nr_pages;
-		pte_t *ptep;
-
-		ptep = pte_offset_kernel(pmd, addr);
-		if (!reuse) {
-			reuse = pte_page(ptep[-1]);
-			set_page_private(reuse, addr - PAGE_SIZE);
-		}
-
-		next = vmemmap_hpage_addr_end(addr, end);
-		nr_pages = (next - addr) >> PAGE_SHIFT;
-		__remap_huge_page_pte_vmemmap(reuse, ptep, addr, nr_pages,
-					      remap_pages);
-	} while (pmd++, addr = next, addr != end);
-
-	flush_tlb_kernel_range(start, end);
-}
-
 static inline void alloc_vmemmap_pages(struct hstate *h, struct list_head *list)
 {
 	int i;
@@ -1736,8 +1716,8 @@ static void alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
 	ptl = vmemmap_pmd_lockptr(pmd);
 
 	spin_lock(ptl);
-	__remap_huge_page_pmd_vmemmap(h, pmd, (unsigned long)head,
-				      &remap_pages);
+	remap_huge_page_pmd_vmemmap(h, pmd, (unsigned long)head, &remap_pages,
+				    __remap_huge_page_pte_vmemmap);
 	if (!freed_vmemmap_hpage_dec(pmd_page(*pmd))) {
 		/*
 		 * Todo:
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 15/24] mm/hugetlb: Use PG_slab to indicate split pmd
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (13 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 14/24] mm/hugetlb: Introduce remap_huge_page_pmd_vmemmap helper Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 16/24] mm/hugetlb: Support freeing vmemmap pages of gigantic page Muchun Song
                   ` (10 subsequent siblings)
  25 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

When we allocate hugetlb page from buddy, we may need split huge pmd
to pte. When we free the hugetlb page, we can merge pte to pmd. So
we need to distinguish whether the previous pmd has been split. The
page table is not allocated from slab. So we can reuse the PG_slab
to indicate that the pmd has been split.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/hugetlb.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 5cc796dc3a0a..c42c27a12df2 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1629,6 +1629,25 @@ static void split_vmemmap_huge_page(struct page *head, pmd_t *pmd)
 	flush_tlb_kernel_range(start, addr);
 }
 
+static inline bool pmd_split(pmd_t *pmd)
+{
+	return PageSlab(pmd_page(*pmd));
+}
+
+static inline void set_pmd_split(pmd_t *pmd)
+{
+	/*
+	 * We should not use slab for page table allocation. So we can set
+	 * PG_slab to indicate that the pmd has been split.
+	 */
+	__SetPageSlab(pmd_page(*pmd));
+}
+
+static inline void clear_pmd_split(pmd_t *pmd)
+{
+	__ClearPageSlab(pmd_page(*pmd));
+}
+
 static void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 {
 	pmd_t *pmd;
@@ -1645,6 +1664,7 @@ static void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 	if (vmemmap_pmd_huge(pmd)) {
 		VM_BUG_ON(!nr_pgtable(h));
 		split_vmemmap_huge_page(head, pmd);
+		set_pmd_split(pmd);
 	}
 
 	remap_huge_page_pmd_vmemmap(h, pmd, (unsigned long)head, &free_pages,
@@ -1718,11 +1738,12 @@ static void alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
 	spin_lock(ptl);
 	remap_huge_page_pmd_vmemmap(h, pmd, (unsigned long)head, &remap_pages,
 				    __remap_huge_page_pte_vmemmap);
-	if (!freed_vmemmap_hpage_dec(pmd_page(*pmd))) {
+	if (!freed_vmemmap_hpage_dec(pmd_page(*pmd)) && pmd_split(pmd)) {
 		/*
 		 * Todo:
 		 * Merge pte to huge pmd if it has ever been split.
 		 */
+		clear_pmd_split(pmd);
 	}
 	spin_unlock(ptl);
 }
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 16/24] mm/hugetlb: Support freeing vmemmap pages of gigantic page
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (14 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 15/24] mm/hugetlb: Use PG_slab to indicate split pmd Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 17/24] mm/hugetlb: Add a BUILD_BUG_ON to check if struct page size is a power of two Muchun Song
                   ` (9 subsequent siblings)
  25 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

The gigantic page is allocated by bootmem, if we want to free the
unused vmemmap pages. We also should allocate the page table. So
we also allocate page tables from bootmem.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 include/linux/hugetlb.h |  3 +++
 mm/hugetlb.c            | 57 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 2561af2ad901..e3aa192f1c39 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -506,6 +506,9 @@ struct hstate {
 struct huge_bootmem_page {
 	struct list_head list;
 	struct hstate *hstate;
+#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+	pte_t *vmemmap_pgtable;
+#endif
 };
 
 struct page *alloc_huge_page(struct vm_area_struct *vma,
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index c42c27a12df2..7072b849af3d 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1410,6 +1410,48 @@ static inline void vmemmap_pgtable_free(struct hstate *h, struct page *page)
 		pte_free_kernel(&init_mm, pte_p);
 }
 
+static unsigned long __init gather_vmemmap_pgtable_prealloc(void)
+{
+	struct huge_bootmem_page *m, *tmp;
+	unsigned long nr_free = 0;
+
+	list_for_each_entry_safe(m, tmp, &huge_boot_pages, list) {
+		struct hstate *h = m->hstate;
+		unsigned int pgtable_size = nr_pgtable(h) << PAGE_SHIFT;
+
+		if (!pgtable_size)
+			continue;
+
+		m->vmemmap_pgtable = memblock_alloc_try_nid(pgtable_size,
+				PAGE_SIZE, 0, MEMBLOCK_ALLOC_ACCESSIBLE,
+				NUMA_NO_NODE);
+		if (!m->vmemmap_pgtable) {
+			nr_free++;
+			list_del(&m->list);
+			memblock_free_early(__pa(m), huge_page_size(h));
+		}
+	}
+
+	return nr_free;
+}
+
+static void __init gather_vmemmap_pgtable_init(struct huge_bootmem_page *m,
+					       struct page *page)
+{
+	int i;
+	struct hstate *h = m->hstate;
+	unsigned long pgtable = (unsigned long)m->vmemmap_pgtable;
+	unsigned int nr = nr_pgtable(h);
+
+	if (!nr)
+		return;
+
+	vmemmap_pgtable_init(page);
+
+	for (i = 0; i < nr; i++, pgtable += PAGE_SIZE)
+		vmemmap_pgtable_deposit(page, (pte_t *)pgtable);
+}
+
 static void __init hugetlb_vmemmap_init(struct hstate *h)
 {
 	unsigned int order = huge_page_order(h);
@@ -1819,6 +1861,16 @@ static inline void vmemmap_pgtable_free(struct hstate *h, struct page *page)
 {
 }
 
+static inline unsigned long gather_vmemmap_pgtable_prealloc(void)
+{
+	return 0;
+}
+
+static inline void gather_vmemmap_pgtable_init(struct huge_bootmem_page *m,
+					       struct page *page)
+{
+}
+
 static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 {
 }
@@ -3080,6 +3132,7 @@ static void __init gather_bootmem_prealloc(void)
 		WARN_ON(page_count(page) != 1);
 		prep_compound_huge_page(page, h->order);
 		WARN_ON(PageReserved(page));
+		gather_vmemmap_pgtable_init(m, page);
 		prep_new_huge_page(h, page, page_to_nid(page));
 		put_page(page); /* free it into the hugepage allocator */
 
@@ -3132,6 +3185,10 @@ static void __init hugetlb_hstate_alloc_pages(struct hstate *h)
 			break;
 		cond_resched();
 	}
+
+	if (hstate_is_gigantic(h))
+		i -= gather_vmemmap_pgtable_prealloc();
+
 	if (i < h->max_huge_pages) {
 		char buf[32];
 
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 17/24] mm/hugetlb: Add a BUILD_BUG_ON to check if struct page size is a power of two
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (15 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 16/24] mm/hugetlb: Support freeing vmemmap pages of gigantic page Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 18/24] mm/hugetlb: Clear PageHWPoison on the non-error memory page Muchun Song
                   ` (8 subsequent siblings)
  25 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

We only can free the unused vmemmap to the buddy system when the
size of struct page is a power of two. So add a BUILD_BUG_ON to
check the illegal case.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/hugetlb.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 7072b849af3d..34706cec21ec 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3817,6 +3817,10 @@ static int __init hugetlb_init(void)
 {
 	int i;
 
+#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+	BUILD_BUG_ON_NOT_POWER_OF_2(sizeof(struct page));
+#endif
+
 	if (!hugepages_supported()) {
 		if (hugetlb_max_hstate || default_hstate_max_huge_pages)
 			pr_warn("HugeTLB: huge pages not supported, ignoring associated command-line parameters\n");
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 18/24] mm/hugetlb: Clear PageHWPoison on the non-error memory page
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (16 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 17/24] mm/hugetlb: Add a BUILD_BUG_ON to check if struct page size is a power of two Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 19/24] mm/hugetlb: Flush work when dissolving hugetlb page Muchun Song
                   ` (7 subsequent siblings)
  25 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

Because we reuse the first tail page, if we set PageHWPosion on a
tail page. It indicates that we may set PageHWPoison on a series
of pages. So we need to clear PageHWPoison on the non-error pages.
We use the head[3].mapping to record the real error page index and
clear non-error page PageHWPoison later.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/hugetlb.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 34706cec21ec..8666cedf9a7b 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1847,6 +1847,21 @@ static inline void free_gigantic_page_comm(struct hstate *h, struct page *page)
 {
 	free_gigantic_page(page, huge_page_order(h));
 }
+
+static inline bool subpage_hwpoison(struct page *head, struct page *page)
+{
+	return page_private(head + 4) == page - head;
+}
+
+static inline void set_subpage_hwpoison(struct page *head, struct page *page)
+{
+	set_page_private(head + 4, page - head);
+}
+
+static inline void clear_subpage_hwpoison(struct page *head)
+{
+	set_page_private(head + 4, 0);
+}
 #else
 static inline void hugetlb_vmemmap_init(struct hstate *h)
 {
@@ -1894,6 +1909,19 @@ static inline void free_gigantic_page_comm(struct hstate *h, struct page *page)
 	free_gigantic_page(page, huge_page_order(h));
 	spin_lock(&hugetlb_lock);
 }
+
+static inline bool subpage_hwpoison(struct page *head, struct page *page)
+{
+	return true;
+}
+
+static inline void set_subpage_hwpoison(struct page *head, struct page *page)
+{
+}
+
+static inline void clear_subpage_hwpoison(struct page *head)
+{
+}
 #endif
 
 static void update_and_free_page(struct hstate *h, struct page *page)
@@ -1918,6 +1946,9 @@ static void __free_hugepage(struct hstate *h, struct page *page)
 				1 << PG_referenced | 1 << PG_dirty |
 				1 << PG_active | 1 << PG_private |
 				1 << PG_writeback);
+
+		if (PageHWPoison(page + i) && !subpage_hwpoison(page, page + i))
+			ClearPageHWPoison(page + i);
 	}
 	VM_BUG_ON_PAGE(hugetlb_cgroup_from_page(page), page);
 	VM_BUG_ON_PAGE(hugetlb_cgroup_from_page_rsvd(page), page);
@@ -2107,6 +2138,7 @@ static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
 	free_huge_page_vmemmap(h, page);
 	/* Must be called before the initialization of @page->lru */
 	vmemmap_pgtable_free(h, page);
+	clear_subpage_hwpoison(page);
 
 	INIT_LIST_HEAD(&page->lru);
 	set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
@@ -2477,6 +2509,7 @@ int dissolve_free_huge_page(struct page *page)
 			SetPageHWPoison(page);
 			ClearPageHWPoison(head);
 		}
+		set_subpage_hwpoison(head, page);
 		list_del(&head->lru);
 		h->free_huge_pages--;
 		h->free_huge_pages_node[nid]--;
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 19/24] mm/hugetlb: Flush work when dissolving hugetlb page
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (17 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 18/24] mm/hugetlb: Clear PageHWPoison on the non-error memory page Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 20/24] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap Muchun Song
                   ` (6 subsequent siblings)
  25 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

We should flush work when dissolving a hugetlb page to make sure that
the hugetlb page is freed to the buddy.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/hugetlb.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 8666cedf9a7b..56c0bf2370ed 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1848,6 +1848,11 @@ static inline void free_gigantic_page_comm(struct hstate *h, struct page *page)
 	free_gigantic_page(page, huge_page_order(h));
 }
 
+static inline void flush_free_huge_page_work(void)
+{
+	flush_work(&hpage_update_work);
+}
+
 static inline bool subpage_hwpoison(struct page *head, struct page *page)
 {
 	return page_private(head + 4) == page - head;
@@ -1910,6 +1915,10 @@ static inline void free_gigantic_page_comm(struct hstate *h, struct page *page)
 	spin_lock(&hugetlb_lock);
 }
 
+static inline void flush_free_huge_page_work(void)
+{
+}
+
 static inline bool subpage_hwpoison(struct page *head, struct page *page)
 {
 	return true;
@@ -2484,6 +2493,7 @@ static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
 int dissolve_free_huge_page(struct page *page)
 {
 	int rc = -EBUSY;
+	bool need_flush = false;
 
 	/* Not to disrupt normal path by vainly holding hugetlb_lock */
 	if (!PageHuge(page))
@@ -2515,10 +2525,19 @@ int dissolve_free_huge_page(struct page *page)
 		h->free_huge_pages_node[nid]--;
 		h->max_huge_pages--;
 		update_and_free_page(h, head);
+		need_flush = true;
 		rc = 0;
 	}
 out:
 	spin_unlock(&hugetlb_lock);
+
+	/*
+	 * We should flush work before return to make sure that
+	 * the hugetlb page is freed to the buddy.
+	 */
+	if (need_flush)
+		flush_free_huge_page_work();
+
 	return rc;
 }
 
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 20/24] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (18 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 19/24] mm/hugetlb: Flush work when dissolving hugetlb page Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-16  2:10   ` Randy Dunlap
  2020-09-15 12:59 ` [RFC PATCH 21/24] mm/hugetlb: Merge pte to huge pmd only for gigantic page Muchun Song
                   ` (5 subsequent siblings)
  25 siblings, 1 reply; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

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

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 .../admin-guide/kernel-parameters.txt         |  9 ++++++++
 Documentation/admin-guide/mm/hugetlbpage.rst  |  3 +++
 mm/hugetlb.c                                  | 23 +++++++++++++++++++
 3 files changed, 35 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 5debfe238027..69d18ef6f66b 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1551,6 +1551,15 @@
 			Documentation/admin-guide/mm/hugetlbpage.rst.
 			Format: size[KMG]
 
+	hugetlb_free_vmemmap=
+			[KNL] When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set,
+			this disables freeing unused vmemmap pages associated
+			each HugeTLB page.
+			Format: { on (default) | off }
+
+			on:  enable the feature
+			off: dosable 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..7d6129ee97dd 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 disables freeing
+	unused vmemmap pages associated 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/mm/hugetlb.c b/mm/hugetlb.c
index 56c0bf2370ed..28c154679838 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1310,6 +1310,8 @@ static void __free_hugepage(struct hstate *h, struct page *page);
 	(__boundary - 1 < (end) - 1) ? __boundary : (end);		\
 })
 
+static bool hugetlb_free_vmemmap_disabled __initdata;
+
 static inline unsigned int nr_free_vmemmap(struct hstate *h)
 {
 	return h->nr_free_vmemmap_pages;
@@ -1457,6 +1459,13 @@ static void __init hugetlb_vmemmap_init(struct hstate *h)
 	unsigned int order = huge_page_order(h);
 	unsigned int vmemmap_pages;
 
+	if (hugetlb_free_vmemmap_disabled) {
+		h->nr_free_vmemmap_pages = 0;
+		pr_info("HugeTLB: disable free vmemmap pages for %s\n",
+			h->name);
+		return;
+	}
+
 	vmemmap_pages = ((1 << order) * sizeof(struct page)) >> PAGE_SHIFT;
 	/*
 	 * The head page and the first tail page not free to buddy system,
@@ -1867,6 +1876,20 @@ static inline void clear_subpage_hwpoison(struct page *head)
 {
 	set_page_private(head + 4, 0);
 }
+
+static int __init early_hugetlb_free_vmemmap_param(char *buf)
+{
+	if (!buf)
+		return -EINVAL;
+
+	if (!strcmp(buf, "off"))
+		hugetlb_free_vmemmap_disabled = true;
+	else if (strcmp(buf, "on"))
+		return -EINVAL;
+
+	return 0;
+}
+early_param("hugetlb_free_vmemmap", early_hugetlb_free_vmemmap_param);
 #else
 static inline void hugetlb_vmemmap_init(struct hstate *h)
 {
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 21/24] mm/hugetlb: Merge pte to huge pmd only for gigantic page
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (19 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 20/24] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-20  9:59   ` Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 22/24] mm/hugetlb: Implement vmemmap_pmd_mkhuge macro Muchun Song
                   ` (4 subsequent siblings)
  25 siblings, 1 reply; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

Merge pte to huge pmd if it has ever been split. Now only support
gigantic page which's vmemmap pages size is an integer multiple of
PMD_SIZE. This is the simplest case to handle.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 include/linux/hugetlb.h |   7 +++
 mm/hugetlb.c            | 104 +++++++++++++++++++++++++++++++++++++++-
 2 files changed, 109 insertions(+), 2 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index e3aa192f1c39..c56df0da7ae5 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -611,6 +611,13 @@ static inline bool vmemmap_pmd_huge(pmd_t *pmd)
 }
 #endif
 
+#ifndef vmemmap_pmd_mkhuge
+static inline pmd_t vmemmap_pmd_mkhuge(struct page *page)
+{
+	return pmd_mkhuge(mk_pmd(page, PAGE_KERNEL));
+}
+#endif
+
 #ifndef VMEMMAP_HPAGE_SHIFT
 #define VMEMMAP_HPAGE_SHIFT		PMD_SHIFT
 #endif
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 28c154679838..3ca36e259b4e 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1759,6 +1759,62 @@ static void __remap_huge_page_pte_vmemmap(struct page *reuse, pte_t *ptep,
 	}
 }
 
+static void __replace_huge_page_pte_vmemmap(pte_t *ptep, unsigned long start,
+					    unsigned int nr, struct page *huge,
+					    struct list_head *free_pages)
+{
+	unsigned long addr;
+	unsigned long end = start + (nr  << PAGE_SHIFT);
+
+	for (addr = start; addr < end; addr += PAGE_SIZE, ptep++) {
+		struct page *page;
+		pte_t old = *ptep;
+		pte_t entry;
+
+		prepare_vmemmap_page(huge);
+
+		entry = mk_pte(huge++, PAGE_KERNEL);
+		VM_WARN_ON(!pte_present(old));
+		page = pte_page(old);
+		list_add(&page->lru, free_pages);
+
+		set_pte_at(&init_mm, addr, ptep, entry);
+	}
+}
+
+static void replace_huge_page_pmd_vmemmap(pmd_t *pmd, unsigned long start,
+					  struct page *huge,
+					  struct list_head *free_pages)
+{
+	unsigned long end = start + VMEMMAP_HPAGE_SIZE;
+
+	flush_cache_vunmap(start, end);
+	__replace_huge_page_pte_vmemmap(pte_offset_kernel(pmd, start), start,
+					VMEMMAP_HPAGE_NR, huge, free_pages);
+	flush_tlb_kernel_range(start, end);
+}
+
+static pte_t *merge_vmemmap_pte(pmd_t *pmdp, unsigned long addr)
+{
+	pte_t *pte;
+	struct page *page;
+
+	pte = pte_offset_kernel(pmdp, addr);
+	page = pte_page(*pte);
+	set_pmd(pmdp, vmemmap_pmd_mkhuge(page));
+
+	return pte;
+}
+
+static void merge_huge_page_pmd_vmemmap(pmd_t *pmd, unsigned long start,
+					struct page *huge,
+					struct list_head *free_pages)
+{
+	replace_huge_page_pmd_vmemmap(pmd, start, huge, free_pages);
+	pte_free_kernel(&init_mm, merge_vmemmap_pte(pmd, start));
+	flush_tlb_kernel_range(start, start + VMEMMAP_HPAGE_SIZE);
+}
+
 static inline void alloc_vmemmap_pages(struct hstate *h, struct list_head *list)
 {
 	int i;
@@ -1772,6 +1828,15 @@ static inline void alloc_vmemmap_pages(struct hstate *h, struct list_head *list)
 	}
 }
 
+static inline void dissolve_compound_page(struct page *page, unsigned int order)
+{
+	int i;
+	unsigned int nr_pages = 1 << order;
+
+	for (i = 1; i < nr_pages; i++)
+		set_page_refcounted(page + i);
+}
+
 static void alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
 {
 	pmd_t *pmd;
@@ -1791,10 +1856,45 @@ static void alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
 				    __remap_huge_page_pte_vmemmap);
 	if (!freed_vmemmap_hpage_dec(pmd_page(*pmd)) && pmd_split(pmd)) {
 		/*
-		 * Todo:
-		 * Merge pte to huge pmd if it has ever been split.
+		 * Merge pte to huge pmd if it has ever been split. Now only
+		 * support gigantic page which's vmemmap pages size is an
+		 * integer multiple of PMD_SIZE. This is the simplest case
+		 * to handle.
 		 */
 		clear_pmd_split(pmd);
+
+		if (IS_ALIGNED(nr_vmemmap(h), VMEMMAP_HPAGE_NR)) {
+			unsigned long addr = (unsigned long)head;
+			unsigned long end = addr + nr_vmemmap_size(h);
+
+			spin_unlock(ptl);
+
+			for (; addr < end; addr += VMEMMAP_HPAGE_SIZE) {
+				void *to;
+				struct page *page;
+
+				page = alloc_pages(GFP_VMEMMAP_PAGE & ~__GFP_NOFAIL,
+						   VMEMMAP_HPAGE_ORDER);
+				if (!page)
+					goto out;
+
+				to = page_to_virt(page);
+				memcpy(to, (void *)addr, VMEMMAP_HPAGE_SIZE);
+
+				/*
+				 * Make sure that any data that writes to the
+				 * @to is made visible to the physical page.
+				 */
+				flush_kernel_vmap_range(to, VMEMMAP_HPAGE_SIZE);
+
+				merge_huge_page_pmd_vmemmap(pmd++, addr, page,
+							    &remap_pages);
+			}
+
+out:
+			free_vmemmap_page_list(&remap_pages);
+			return;
+		}
 	}
 	spin_unlock(ptl);
 }
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 22/24] mm/hugetlb: Implement vmemmap_pmd_mkhuge macro
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (20 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 21/24] mm/hugetlb: Merge pte to huge pmd only for gigantic page Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 23/24] mm/hugetlb: Gather discrete indexes of tail page Muchun Song
                   ` (3 subsequent siblings)
  25 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

In vmemmap_populate_hugepages(), we use PAGE_KERNEL_LARGE for
huge page mapping. So we can inplement vmemmap_pmd_mkhuge macro
to do that.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 arch/x86/include/asm/hugetlb.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/include/asm/hugetlb.h b/arch/x86/include/asm/hugetlb.h
index 7c3eb60c2198..9f9e19dd0578 100644
--- a/arch/x86/include/asm/hugetlb.h
+++ b/arch/x86/include/asm/hugetlb.h
@@ -15,6 +15,14 @@ static inline bool vmemmap_pmd_huge(pmd_t *pmd)
 {
 	return pmd_large(*pmd);
 }
+
+#define vmemmap_pmd_mkhuge vmemmap_pmd_mkhuge
+static inline pmd_t vmemmap_pmd_mkhuge(struct page *page)
+{
+	pte_t entry = pfn_pte(page_to_pfn(page), PAGE_KERNEL_LARGE);
+
+	return __pmd(pte_val(entry));
+}
 #endif
 
 #define hugepages_supported() boot_cpu_has(X86_FEATURE_PSE)
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 23/24] mm/hugetlb: Gather discrete indexes of tail page
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (21 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 22/24] mm/hugetlb: Implement vmemmap_pmd_mkhuge macro Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-15 12:59 ` [RFC PATCH 24/24] mm/hugetlb: Add BUILD_BUG_ON to catch invalid usage of tail struct page Muchun Song
                   ` (2 subsequent siblings)
  25 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

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

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 include/linux/hugetlb.h        | 13 +++++++++++++
 include/linux/hugetlb_cgroup.h | 15 +++++++++------
 mm/hugetlb.c                   | 18 +++++++++---------
 3 files changed, 31 insertions(+), 15 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index c56df0da7ae5..358550a53555 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -28,6 +28,19 @@ typedef struct { unsigned long pd; } hugepd_t;
 #include <linux/shm.h>
 #include <asm/tlbflush.h>
 
+enum {
+	SUBPAGE_INDEX_ACTIVE = 1,	/* reuse page flags of PG_private */
+	SUBPAGE_INDEX_TEMPORARY,	/* reuse page->mapping */
+#ifdef CONFIG_CGROUP_HUGETLB
+	SUBPAGE_INDEX_CGROUP = SUBPAGE_INDEX_TEMPORARY,/* reuse page->private */
+	SUBPAGE_INDEX_CGROUP_RSVD,	/* reuse page->private */
+#endif
+#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+	SUBPAGE_INDEX_HWPOISON,		/* reuse page->private */
+#endif
+	NR_USED_SUBPAGE,
+};
+
 struct hugepage_subpool {
 	spinlock_t lock;
 	long count;
diff --git a/include/linux/hugetlb_cgroup.h b/include/linux/hugetlb_cgroup.h
index 2ad6e92f124a..3d3c1c49efe4 100644
--- a/include/linux/hugetlb_cgroup.h
+++ b/include/linux/hugetlb_cgroup.h
@@ -24,8 +24,9 @@ struct file_region;
 /*
  * 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
 
@@ -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.c b/mm/hugetlb.c
index 3ca36e259b4e..e66c3f10c583 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1964,17 +1964,17 @@ static inline void flush_free_huge_page_work(void)
 
 static inline bool subpage_hwpoison(struct page *head, struct page *page)
 {
-	return page_private(head + 4) == page - head;
+	return page_private(head + SUBPAGE_INDEX_HWPOISON) == page - head;
 }
 
 static inline void set_subpage_hwpoison(struct page *head, struct page *page)
 {
-	set_page_private(head + 4, page - head);
+	set_page_private(head + SUBPAGE_INDEX_HWPOISON, page - head);
 }
 
 static inline void clear_subpage_hwpoison(struct page *head)
 {
-	set_page_private(head + 4, 0);
+	set_page_private(head + SUBPAGE_INDEX_HWPOISON, 0);
 }
 
 static int __init early_hugetlb_free_vmemmap_param(char *buf)
@@ -2114,20 +2114,20 @@ struct hstate *size_to_hstate(unsigned long size)
 bool page_huge_active(struct page *page)
 {
 	VM_BUG_ON_PAGE(!PageHuge(page), page);
-	return PageHead(page) && PagePrivate(&page[1]);
+	return PageHead(page) && PagePrivate(&page[SUBPAGE_INDEX_ACTIVE]);
 }
 
 /* never called for tail page */
 static void set_page_huge_active(struct page *page)
 {
 	VM_BUG_ON_PAGE(!PageHeadHuge(page), page);
-	SetPagePrivate(&page[1]);
+	SetPagePrivate(&page[SUBPAGE_INDEX_ACTIVE]);
 }
 
 static void clear_page_huge_active(struct page *page)
 {
 	VM_BUG_ON_PAGE(!PageHeadHuge(page), page);
-	ClearPagePrivate(&page[1]);
+	ClearPagePrivate(&page[SUBPAGE_INDEX_ACTIVE]);
 }
 
 /*
@@ -2139,17 +2139,17 @@ static inline bool PageHugeTemporary(struct page *page)
 	if (!PageHuge(page))
 		return false;
 
-	return (unsigned long)page[2].mapping == -1U;
+	return (unsigned long)page[SUBPAGE_INDEX_TEMPORARY].mapping == -1U;
 }
 
 static inline void SetPageHugeTemporary(struct page *page)
 {
-	page[2].mapping = (void *)-1U;
+	page[SUBPAGE_INDEX_TEMPORARY].mapping = (void *)-1U;
 }
 
 static inline void ClearPageHugeTemporary(struct page *page)
 {
-	page[2].mapping = NULL;
+	page[SUBPAGE_INDEX_TEMPORARY].mapping = NULL;
 }
 
 static void __free_huge_page(struct page *page)
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* [RFC PATCH 24/24] mm/hugetlb: Add BUILD_BUG_ON to catch invalid usage of tail struct page
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (22 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 23/24] mm/hugetlb: Gather discrete indexes of tail page Muchun Song
@ 2020-09-15 12:59 ` Muchun Song
  2020-09-15 14:32 ` [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Matthew Wilcox
  2020-09-29 21:58 ` Mike Kravetz
  25 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-15 12:59 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel, Muchun Song

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

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/hugetlb.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index e66c3f10c583..63995ba74b6b 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3994,6 +3994,8 @@ static int __init hugetlb_init(void)
 
 #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
 	BUILD_BUG_ON_NOT_POWER_OF_2(sizeof(struct page));
+	BUILD_BUG_ON(NR_USED_SUBPAGE >=
+		     RESERVE_VMEMMAP_SIZE / sizeof(struct page));
 #endif
 
 	if (!hugepages_supported()) {
-- 
2.20.1



^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (23 preceding siblings ...)
  2020-09-15 12:59 ` [RFC PATCH 24/24] mm/hugetlb: Add BUILD_BUG_ON to catch invalid usage of tail struct page Muchun Song
@ 2020-09-15 14:32 ` Matthew Wilcox
  2020-09-15 14:53   ` Dave Hansen
  2020-09-15 15:28   ` [External] " Muchun Song
  2020-09-29 21:58 ` Mike Kravetz
  25 siblings, 2 replies; 48+ messages in thread
From: Matthew Wilcox @ 2020-09-15 14:32 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, linux-doc, linux-kernel, linux-mm,
	linux-fsdevel

On Tue, Sep 15, 2020 at 08:59:23PM +0800, Muchun Song wrote:
> This patch series will free some vmemmap pages(struct page structures)
> associated with each hugetlbpage when preallocated to save memory.

It would be lovely to be able to do this.  Unfortunately, it's completely
impossible right now.  Consider, for example, get_user_pages() called
on the fifth page of a hugetlb page.

I've spent a lot of time thinking about this, and there's a lot of work
that needs to happen before we can do this, mostly in device drivers.
Do you want to help?  It's a multi-year project.


^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page
  2020-09-15 14:32 ` [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Matthew Wilcox
@ 2020-09-15 14:53   ` Dave Hansen
  2020-09-15 15:28   ` [External] " Muchun Song
  1 sibling, 0 replies; 48+ messages in thread
From: Dave Hansen @ 2020-09-15 14:53 UTC (permalink / raw)
  To: Matthew Wilcox, 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, linux-doc, linux-kernel, linux-mm,
	linux-fsdevel

On 9/15/20 7:32 AM, Matthew Wilcox wrote:
> On Tue, Sep 15, 2020 at 08:59:23PM +0800, Muchun Song wrote:
>> This patch series will free some vmemmap pages(struct page structures)
>> associated with each hugetlbpage when preallocated to save memory.
> It would be lovely to be able to do this.  Unfortunately, it's completely
> impossible right now.  Consider, for example, get_user_pages() called
> on the fifth page of a hugetlb page.

Yeah, exactly.

Does this series survive the in-kernel selftests/?  If so, sounds like
we need to add a new selftest.


^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [External] Re: [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page
  2020-09-15 14:32 ` [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Matthew Wilcox
  2020-09-15 14:53   ` Dave Hansen
@ 2020-09-15 15:28   ` Muchun Song
  2020-09-15 15:42     ` Matthew Wilcox
  1 sibling, 1 reply; 48+ messages in thread
From: Muchun Song @ 2020-09-15 15:28 UTC (permalink / raw)
  To: Matthew Wilcox
  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, almasrymina, David Rientjes,
	linux-doc, LKML, Linux Memory Management List, linux-fsdevel

On Tue, Sep 15, 2020 at 10:32 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Tue, Sep 15, 2020 at 08:59:23PM +0800, Muchun Song wrote:
> > This patch series will free some vmemmap pages(struct page structures)
> > associated with each hugetlbpage when preallocated to save memory.
>
> It would be lovely to be able to do this.  Unfortunately, it's completely
> impossible right now.  Consider, for example, get_user_pages() called
> on the fifth page of a hugetlb page.

Can you elaborate on the problem? Thanks so much.

>
> I've spent a lot of time thinking about this, and there's a lot of work
> that needs to happen before we can do this, mostly in device drivers.
> Do you want to help?  It's a multi-year project.

Welcome, we can work together.


-- 
Yours,
Muchun


^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [External] Re: [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page
  2020-09-15 15:28   ` [External] " Muchun Song
@ 2020-09-15 15:42     ` Matthew Wilcox
  2020-09-15 17:32       ` Muchun Song
  0 siblings, 1 reply; 48+ messages in thread
From: Matthew Wilcox @ 2020-09-15 15:42 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, almasrymina, David Rientjes,
	linux-doc, LKML, Linux Memory Management List, linux-fsdevel

On Tue, Sep 15, 2020 at 11:28:01PM +0800, Muchun Song wrote:
> On Tue, Sep 15, 2020 at 10:32 PM Matthew Wilcox <willy@infradead.org> wrote:
> >
> > On Tue, Sep 15, 2020 at 08:59:23PM +0800, Muchun Song wrote:
> > > This patch series will free some vmemmap pages(struct page structures)
> > > associated with each hugetlbpage when preallocated to save memory.
> >
> > It would be lovely to be able to do this.  Unfortunately, it's completely
> > impossible right now.  Consider, for example, get_user_pages() called
> > on the fifth page of a hugetlb page.
> 
> Can you elaborate on the problem? Thanks so much.

OK, let's say you want to do a 2kB I/O to offset 0x5000 of a 2MB page
on a 4kB base page system.  Today, that results in a bio_vec containing
{head+5, 0, 0x800}.  Then we call page_to_phys() on that (head+5) struct
page to get the physical address of the I/O, and we turn it into a struct
scatterlist, which similarly has a reference to the page (head+5).

If you're returning page (head+1) from get_user_pages(), all the
calculations will be wrong and you'll do DMA to the wrong address.

What needs to happen is a conversion to get_user_bvecs().  That way we
can return a bvec which is {head, 0x5000, 0x800} and the calculations
will work.  So that's going to involve touching a lot of device drivers.
Christoph has a start on it here:
http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/gup-bvec

Overlapping with that is a desire to change the biovec so that it
only stores {phys_addr, length} rather than {page, offset, length}.
We're also going to have to rework the scatterlist so that it doesn't
carry a struct page either.


^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [External] Re: [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page
  2020-09-15 15:42     ` Matthew Wilcox
@ 2020-09-15 17:32       ` Muchun Song
  2020-09-15 17:39         ` Matthew Wilcox
  0 siblings, 1 reply; 48+ messages in thread
From: Muchun Song @ 2020-09-15 17:32 UTC (permalink / raw)
  To: Matthew Wilcox
  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, almasrymina, David Rientjes,
	linux-doc, LKML, Linux Memory Management List, linux-fsdevel

On Tue, Sep 15, 2020 at 11:42 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Tue, Sep 15, 2020 at 11:28:01PM +0800, Muchun Song wrote:
> > On Tue, Sep 15, 2020 at 10:32 PM Matthew Wilcox <willy@infradead.org> wrote:
> > >
> > > On Tue, Sep 15, 2020 at 08:59:23PM +0800, Muchun Song wrote:
> > > > This patch series will free some vmemmap pages(struct page structures)
> > > > associated with each hugetlbpage when preallocated to save memory.
> > >
> > > It would be lovely to be able to do this.  Unfortunately, it's completely
> > > impossible right now.  Consider, for example, get_user_pages() called
> > > on the fifth page of a hugetlb page.
> >
> > Can you elaborate on the problem? Thanks so much.
>
> OK, let's say you want to do a 2kB I/O to offset 0x5000 of a 2MB page
> on a 4kB base page system.  Today, that results in a bio_vec containing
> {head+5, 0, 0x800}.  Then we call page_to_phys() on that (head+5) struct
> page to get the physical address of the I/O, and we turn it into a struct
> scatterlist, which similarly has a reference to the page (head+5).

As I know, in this case, the get_user_pages() will get a reference
to the head page (head+0) before returning such that the hugetlb
page can not be freed. Although get_user_pages() returns the
page (head+5) and the scatterlist has a reference to the page
(head+5), this patch series can handle this situation. I can not
figure out where the problem is. What I missed? Thanks.

>
> If you're returning page (head+1) from get_user_pages(), all the
> calculations will be wrong and you'll do DMA to the wrong address.
>
> What needs to happen is a conversion to get_user_bvecs().  That way we
> can return a bvec which is {head, 0x5000, 0x800} and the calculations
> will work.  So that's going to involve touching a lot of device drivers.
> Christoph has a start on it here:
> http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/gup-bvec
>
> Overlapping with that is a desire to change the biovec so that it
> only stores {phys_addr, length} rather than {page, offset, length}.
> We're also going to have to rework the scatterlist so that it doesn't
> carry a struct page either.



-- 
Yours,
Muchun


^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [External] Re: [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page
  2020-09-15 17:32       ` Muchun Song
@ 2020-09-15 17:39         ` Matthew Wilcox
  2020-09-15 18:03           ` Muchun Song
  0 siblings, 1 reply; 48+ messages in thread
From: Matthew Wilcox @ 2020-09-15 17:39 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, almasrymina, David Rientjes,
	linux-doc, LKML, Linux Memory Management List, linux-fsdevel

On Wed, Sep 16, 2020 at 01:32:46AM +0800, Muchun Song wrote:
> On Tue, Sep 15, 2020 at 11:42 PM Matthew Wilcox <willy@infradead.org> wrote:
> >
> > On Tue, Sep 15, 2020 at 11:28:01PM +0800, Muchun Song wrote:
> > > On Tue, Sep 15, 2020 at 10:32 PM Matthew Wilcox <willy@infradead.org> wrote:
> > > >
> > > > On Tue, Sep 15, 2020 at 08:59:23PM +0800, Muchun Song wrote:
> > > > > This patch series will free some vmemmap pages(struct page structures)
> > > > > associated with each hugetlbpage when preallocated to save memory.
> > > >
> > > > It would be lovely to be able to do this.  Unfortunately, it's completely
> > > > impossible right now.  Consider, for example, get_user_pages() called
> > > > on the fifth page of a hugetlb page.
> > >
> > > Can you elaborate on the problem? Thanks so much.
> >
> > OK, let's say you want to do a 2kB I/O to offset 0x5000 of a 2MB page
> > on a 4kB base page system.  Today, that results in a bio_vec containing
> > {head+5, 0, 0x800}.  Then we call page_to_phys() on that (head+5) struct
> > page to get the physical address of the I/O, and we turn it into a struct
> > scatterlist, which similarly has a reference to the page (head+5).
> 
> As I know, in this case, the get_user_pages() will get a reference
> to the head page (head+0) before returning such that the hugetlb
> page can not be freed. Although get_user_pages() returns the
> page (head+5) and the scatterlist has a reference to the page
> (head+5), this patch series can handle this situation. I can not
> figure out where the problem is. What I missed? Thanks.

You freed pages 4-511 from the vmemmap so they could be used for
something else.  Page 5 isn't there any more.  So if you return head+5,
then when we complete the I/O, we'll look for the compound_head() of
head+5 and we won't find head.



^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [External] Re: [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page
  2020-09-15 17:39         ` Matthew Wilcox
@ 2020-09-15 18:03           ` Muchun Song
  2020-09-15 18:15             ` Matthew Wilcox
  0 siblings, 1 reply; 48+ messages in thread
From: Muchun Song @ 2020-09-15 18:03 UTC (permalink / raw)
  To: Matthew Wilcox
  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, almasrymina, David Rientjes,
	linux-doc, LKML, Linux Memory Management List, linux-fsdevel

On Wed, Sep 16, 2020 at 1:39 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Wed, Sep 16, 2020 at 01:32:46AM +0800, Muchun Song wrote:
> > On Tue, Sep 15, 2020 at 11:42 PM Matthew Wilcox <willy@infradead.org> wrote:
> > >
> > > On Tue, Sep 15, 2020 at 11:28:01PM +0800, Muchun Song wrote:
> > > > On Tue, Sep 15, 2020 at 10:32 PM Matthew Wilcox <willy@infradead.org> wrote:
> > > > >
> > > > > On Tue, Sep 15, 2020 at 08:59:23PM +0800, Muchun Song wrote:
> > > > > > This patch series will free some vmemmap pages(struct page structures)
> > > > > > associated with each hugetlbpage when preallocated to save memory.
> > > > >
> > > > > It would be lovely to be able to do this.  Unfortunately, it's completely
> > > > > impossible right now.  Consider, for example, get_user_pages() called
> > > > > on the fifth page of a hugetlb page.
> > > >
> > > > Can you elaborate on the problem? Thanks so much.
> > >
> > > OK, let's say you want to do a 2kB I/O to offset 0x5000 of a 2MB page
> > > on a 4kB base page system.  Today, that results in a bio_vec containing
> > > {head+5, 0, 0x800}.  Then we call page_to_phys() on that (head+5) struct
> > > page to get the physical address of the I/O, and we turn it into a struct
> > > scatterlist, which similarly has a reference to the page (head+5).
> >
> > As I know, in this case, the get_user_pages() will get a reference
> > to the head page (head+0) before returning such that the hugetlb
> > page can not be freed. Although get_user_pages() returns the
> > page (head+5) and the scatterlist has a reference to the page
> > (head+5), this patch series can handle this situation. I can not
> > figure out where the problem is. What I missed? Thanks.
>
> You freed pages 4-511 from the vmemmap so they could be used for
> something else.  Page 5 isn't there any more.  So if you return head+5,
> then when we complete the I/O, we'll look for the compound_head() of
> head+5 and we won't find head.
>

We do not free pages 4-511 from the vmemmap. Actually, we only
free pages 128-511 from the vmemmap.

The 512 struct pages occupy 8 pages of physical memory. We only
free 6 physical page frames to the buddy. But we will create a new
mapping just like below. The virtual address of the freed pages will
remap to the second page frame. So the second page frame is
reused.

When a hugetlbpage is preallocated, we can change the mapping to
bellow.

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

As you can see, we reuse the first tail page.

-- 
Yours,
Muchun


^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [External] Re: [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page
  2020-09-15 18:03           ` Muchun Song
@ 2020-09-15 18:15             ` Matthew Wilcox
  2020-09-16  2:45               ` Muchun Song
  0 siblings, 1 reply; 48+ messages in thread
From: Matthew Wilcox @ 2020-09-15 18:15 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, almasrymina, David Rientjes,
	linux-doc, LKML, Linux Memory Management List, linux-fsdevel

On Wed, Sep 16, 2020 at 02:03:15AM +0800, Muchun Song wrote:
> On Wed, Sep 16, 2020 at 1:39 AM Matthew Wilcox <willy@infradead.org> wrote:
> >
> > On Wed, Sep 16, 2020 at 01:32:46AM +0800, Muchun Song wrote:
> > > On Tue, Sep 15, 2020 at 11:42 PM Matthew Wilcox <willy@infradead.org> wrote:
> > > >
> > > > On Tue, Sep 15, 2020 at 11:28:01PM +0800, Muchun Song wrote:
> > > > > On Tue, Sep 15, 2020 at 10:32 PM Matthew Wilcox <willy@infradead.org> wrote:
> > > > > >
> > > > > > On Tue, Sep 15, 2020 at 08:59:23PM +0800, Muchun Song wrote:
> > > > > > > This patch series will free some vmemmap pages(struct page structures)
> > > > > > > associated with each hugetlbpage when preallocated to save memory.
> > > > > >
> > > > > > It would be lovely to be able to do this.  Unfortunately, it's completely
> > > > > > impossible right now.  Consider, for example, get_user_pages() called
> > > > > > on the fifth page of a hugetlb page.
> > > > >
> > > > > Can you elaborate on the problem? Thanks so much.
> > > >
> > > > OK, let's say you want to do a 2kB I/O to offset 0x5000 of a 2MB page
> > > > on a 4kB base page system.  Today, that results in a bio_vec containing
> > > > {head+5, 0, 0x800}.  Then we call page_to_phys() on that (head+5) struct
> > > > page to get the physical address of the I/O, and we turn it into a struct
> > > > scatterlist, which similarly has a reference to the page (head+5).
> > >
> > > As I know, in this case, the get_user_pages() will get a reference
> > > to the head page (head+0) before returning such that the hugetlb
> > > page can not be freed. Although get_user_pages() returns the
> > > page (head+5) and the scatterlist has a reference to the page
> > > (head+5), this patch series can handle this situation. I can not
> > > figure out where the problem is. What I missed? Thanks.
> >
> > You freed pages 4-511 from the vmemmap so they could be used for
> > something else.  Page 5 isn't there any more.  So if you return head+5,
> > then when we complete the I/O, we'll look for the compound_head() of
> > head+5 and we won't find head.
> 
> We do not free pages 4-511 from the vmemmap. Actually, we only
> free pages 128-511 from the vmemmap.
> 
> The 512 struct pages occupy 8 pages of physical memory. We only
> free 6 physical page frames to the buddy. But we will create a new
> mapping just like below. The virtual address of the freed pages will
> remap to the second page frame. So the second page frame is
> reused.

Oh!  I get what you're doing now.

For the vmemmap case, you free the last N-2 physical pages but map the
second physical page multiple times.  So for the 512 pages case, we
see pages:

abcdefgh | ijklmnop | ijklmnop | ijklmnop | ijklmnop | ijklmnop | ijklmnop ...

Huh.  I think that might work, except for PageHWPoison.  I'll go back
to your patch series and look at that some more.



^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [RFC PATCH 20/24] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap
  2020-09-15 12:59 ` [RFC PATCH 20/24] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap Muchun Song
@ 2020-09-16  2:10   ` Randy Dunlap
  2020-09-16  2:50     ` [External] " Muchun Song
  0 siblings, 1 reply; 48+ messages in thread
From: Randy Dunlap @ 2020-09-16  2:10 UTC (permalink / raw)
  To: Muchun Song, corbet, mike.kravetz, tglx, mingo, bp, x86, hpa,
	dave.hansen, luto, peterz, viro, akpm, paulmck, mchehab+huawei,
	pawan.kumar.gupta, oneukum, anshuman.khandual, jroedel,
	almasrymina, rientjes
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel

Hi,
Please see comments below.

On 9/15/20 5:59 AM, Muchun Song wrote:
> Add a kernel parameter hugetlb_free_vmemmap to disable the feature of
> freeing unused vmemmap pages associated with each hugetlb page on boot.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  .../admin-guide/kernel-parameters.txt         |  9 ++++++++
>  Documentation/admin-guide/mm/hugetlbpage.rst  |  3 +++
>  mm/hugetlb.c                                  | 23 +++++++++++++++++++
>  3 files changed, 35 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 5debfe238027..69d18ef6f66b 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1551,6 +1551,15 @@
>  			Documentation/admin-guide/mm/hugetlbpage.rst.
>  			Format: size[KMG]
>  
> +	hugetlb_free_vmemmap=
> +			[KNL] When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set,
> +			this disables freeing unused vmemmap pages associated

			this controls

> +			each HugeTLB page.

			with each HugeTLB page.

> +			Format: { on (default) | off }
> +
> +			on:  enable the feature
> +			off: dosable the feature

			     disable

> +
>  	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..7d6129ee97dd 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.

insert blank line here.

> +hugetlb_free_vmemmap
> +	When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set, this disables freeing
> +	unused vmemmap pages associated 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.


-- 
~Randy



^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [RFC PATCH 03/24] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP
  2020-09-15 12:59 ` [RFC PATCH 03/24] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
@ 2020-09-16  2:13   ` Randy Dunlap
  2020-09-29 23:41   ` Mike Kravetz
  1 sibling, 0 replies; 48+ messages in thread
From: Randy Dunlap @ 2020-09-16  2:13 UTC (permalink / raw)
  To: Muchun Song, corbet, mike.kravetz, tglx, mingo, bp, x86, hpa,
	dave.hansen, luto, peterz, viro, akpm, paulmck, mchehab+huawei,
	pawan.kumar.gupta, oneukum, anshuman.khandual, jroedel,
	almasrymina, rientjes
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel

On 9/15/20 5:59 AM, Muchun Song wrote:
> The purpose of introducing HUGETLB_PAGE_FREE_VMEMMAP is to configure
> whether to enable the feature of freeing unused vmemmap associated
> with HugeTLB pages.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  fs/Kconfig | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/fs/Kconfig b/fs/Kconfig
> index 976e8b9033c4..61e9c08096ca 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -245,6 +245,21 @@ config HUGETLBFS
>  config HUGETLB_PAGE
>  	def_bool HUGETLBFS
>  
> +config HUGETLB_PAGE_FREE_VMEMMAP
> +	bool "Free unused vmemmap associated with HugeTLB pages"
> +	default n
> +	depends on HUGETLB_PAGE
> +	depends on SPARSEMEM_VMEMMAP
> +	depends on HAVE_BOOTMEM_INFO_NODE
> +	help
> +	  There are many struct page structure associated with each HugeTLB

	                             structures

> +	  page. But we only use a few struct page structure. In this case,

	                                          structures.

> +	  it waste some memory. It is better to free the unused struct page

	  it wastes

> +	  structures to buddy system which can save some memory. For
> +	  architectures that support it, say Y here.
> +
> +	  If unsure, say N.
> +
>  config MEMFD_CREATE
>  	def_bool TMPFS || HUGETLBFS
>  
> 


-- 
~Randy



^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [External] Re: [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page
  2020-09-15 18:15             ` Matthew Wilcox
@ 2020-09-16  2:45               ` Muchun Song
  0 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-16  2:45 UTC (permalink / raw)
  To: Matthew Wilcox
  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, almasrymina, David Rientjes,
	linux-doc, LKML, Linux Memory Management List, linux-fsdevel

On Wed, Sep 16, 2020 at 2:15 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Wed, Sep 16, 2020 at 02:03:15AM +0800, Muchun Song wrote:
> > On Wed, Sep 16, 2020 at 1:39 AM Matthew Wilcox <willy@infradead.org> wrote:
> > >
> > > On Wed, Sep 16, 2020 at 01:32:46AM +0800, Muchun Song wrote:
> > > > On Tue, Sep 15, 2020 at 11:42 PM Matthew Wilcox <willy@infradead.org> wrote:
> > > > >
> > > > > On Tue, Sep 15, 2020 at 11:28:01PM +0800, Muchun Song wrote:
> > > > > > On Tue, Sep 15, 2020 at 10:32 PM Matthew Wilcox <willy@infradead.org> wrote:
> > > > > > >
> > > > > > > On Tue, Sep 15, 2020 at 08:59:23PM +0800, Muchun Song wrote:
> > > > > > > > This patch series will free some vmemmap pages(struct page structures)
> > > > > > > > associated with each hugetlbpage when preallocated to save memory.
> > > > > > >
> > > > > > > It would be lovely to be able to do this.  Unfortunately, it's completely
> > > > > > > impossible right now.  Consider, for example, get_user_pages() called
> > > > > > > on the fifth page of a hugetlb page.
> > > > > >
> > > > > > Can you elaborate on the problem? Thanks so much.
> > > > >
> > > > > OK, let's say you want to do a 2kB I/O to offset 0x5000 of a 2MB page
> > > > > on a 4kB base page system.  Today, that results in a bio_vec containing
> > > > > {head+5, 0, 0x800}.  Then we call page_to_phys() on that (head+5) struct
> > > > > page to get the physical address of the I/O, and we turn it into a struct
> > > > > scatterlist, which similarly has a reference to the page (head+5).
> > > >
> > > > As I know, in this case, the get_user_pages() will get a reference
> > > > to the head page (head+0) before returning such that the hugetlb
> > > > page can not be freed. Although get_user_pages() returns the
> > > > page (head+5) and the scatterlist has a reference to the page
> > > > (head+5), this patch series can handle this situation. I can not
> > > > figure out where the problem is. What I missed? Thanks.
> > >
> > > You freed pages 4-511 from the vmemmap so they could be used for
> > > something else.  Page 5 isn't there any more.  So if you return head+5,
> > > then when we complete the I/O, we'll look for the compound_head() of
> > > head+5 and we won't find head.
> >
> > We do not free pages 4-511 from the vmemmap. Actually, we only
> > free pages 128-511 from the vmemmap.
> >
> > The 512 struct pages occupy 8 pages of physical memory. We only
> > free 6 physical page frames to the buddy. But we will create a new
> > mapping just like below. The virtual address of the freed pages will
> > remap to the second page frame. So the second page frame is
> > reused.
>
> Oh!  I get what you're doing now.
>
> For the vmemmap case, you free the last N-2 physical pages but map the
> second physical page multiple times.  So for the 512 pages case, we
> see pages:
>
> abcdefgh | ijklmnop | ijklmnop | ijklmnop | ijklmnop | ijklmnop | ijklmnop ...

Yeah, great. You are right.

>
> Huh.  I think that might work, except for PageHWPoison.  I'll go back
> to your patch series and look at that some more.
>

The PageHWPoison also is considered in the patch series. Looking
forward to your suggestions. Thanks.


-- 
Yours,
Muchun


^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [External] Re: [RFC PATCH 20/24] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap
  2020-09-16  2:10   ` Randy Dunlap
@ 2020-09-16  2:50     ` Muchun Song
  0 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-16  2:50 UTC (permalink / raw)
  To: Randy Dunlap
  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, oneukum,
	anshuman.khandual, jroedel, almasrymina, David Rientjes,
	linux-doc, LKML, Linux Memory Management List, linux-fsdevel

On Wed, Sep 16, 2020 at 10:11 AM Randy Dunlap <rdunlap@infradead.org> wrote:
>
> Hi,
> Please see comments below.
>
> On 9/15/20 5:59 AM, Muchun Song wrote:
> > Add a kernel parameter hugetlb_free_vmemmap to disable the feature of
> > freeing unused vmemmap pages associated with each hugetlb page on boot.
> >
> > Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> > ---
> >  .../admin-guide/kernel-parameters.txt         |  9 ++++++++
> >  Documentation/admin-guide/mm/hugetlbpage.rst  |  3 +++
> >  mm/hugetlb.c                                  | 23 +++++++++++++++++++
> >  3 files changed, 35 insertions(+)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 5debfe238027..69d18ef6f66b 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -1551,6 +1551,15 @@
> >                       Documentation/admin-guide/mm/hugetlbpage.rst.
> >                       Format: size[KMG]
> >
> > +     hugetlb_free_vmemmap=
> > +                     [KNL] When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set,
> > +                     this disables freeing unused vmemmap pages associated
>
>                         this controls
>
> > +                     each HugeTLB page.
>
>                         with each HugeTLB page.
>
> > +                     Format: { on (default) | off }
> > +
> > +                     on:  enable the feature
> > +                     off: dosable the feature
>
>                              disable
>
> > +
> >       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..7d6129ee97dd 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.
>
> insert blank line here.
>
> > +hugetlb_free_vmemmap
> > +     When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set, this disables freeing
> > +     unused vmemmap pages associated 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.
>

Thanks for your comments.

>
> --
> ~Randy
>


-- 
Yours,
Muchun


^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [RFC PATCH 21/24] mm/hugetlb: Merge pte to huge pmd only for gigantic page
  2020-09-15 12:59 ` [RFC PATCH 21/24] mm/hugetlb: Merge pte to huge pmd only for gigantic page Muchun Song
@ 2020-09-20  9:59   ` Muchun Song
  0 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-20  9:59 UTC (permalink / raw)
  To: 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
  Cc: linux-doc, LKML, Linux Memory Management List, linux-fsdevel

On Tue, Sep 15, 2020 at 9:03 PM Muchun Song <songmuchun@bytedance.com> wrote:
>
> Merge pte to huge pmd if it has ever been split. Now only support
> gigantic page which's vmemmap pages size is an integer multiple of
> PMD_SIZE. This is the simplest case to handle.
>
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  include/linux/hugetlb.h |   7 +++
>  mm/hugetlb.c            | 104 +++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 109 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index e3aa192f1c39..c56df0da7ae5 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -611,6 +611,13 @@ static inline bool vmemmap_pmd_huge(pmd_t *pmd)
>  }
>  #endif
>
> +#ifndef vmemmap_pmd_mkhuge
> +static inline pmd_t vmemmap_pmd_mkhuge(struct page *page)
> +{
> +       return pmd_mkhuge(mk_pmd(page, PAGE_KERNEL));
> +}
> +#endif
> +
>  #ifndef VMEMMAP_HPAGE_SHIFT
>  #define VMEMMAP_HPAGE_SHIFT            PMD_SHIFT
>  #endif
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 28c154679838..3ca36e259b4e 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1759,6 +1759,62 @@ static void __remap_huge_page_pte_vmemmap(struct page *reuse, pte_t *ptep,
>         }
>  }
>
> +static void __replace_huge_page_pte_vmemmap(pte_t *ptep, unsigned long start,
> +                                           unsigned int nr, struct page *huge,
> +                                           struct list_head *free_pages)
> +{
> +       unsigned long addr;
> +       unsigned long end = start + (nr  << PAGE_SHIFT);
> +
> +       for (addr = start; addr < end; addr += PAGE_SIZE, ptep++) {
> +               struct page *page;
> +               pte_t old = *ptep;
> +               pte_t entry;
> +
> +               prepare_vmemmap_page(huge);
> +
> +               entry = mk_pte(huge++, PAGE_KERNEL);
> +               VM_WARN_ON(!pte_present(old));
> +               page = pte_page(old);
> +               list_add(&page->lru, free_pages);
> +
> +               set_pte_at(&init_mm, addr, ptep, entry);
> +       }
> +}
> +
> +static void replace_huge_page_pmd_vmemmap(pmd_t *pmd, unsigned long start,
> +                                         struct page *huge,
> +                                         struct list_head *free_pages)
> +{
> +       unsigned long end = start + VMEMMAP_HPAGE_SIZE;
> +
> +       flush_cache_vunmap(start, end);
> +       __replace_huge_page_pte_vmemmap(pte_offset_kernel(pmd, start), start,
> +                                       VMEMMAP_HPAGE_NR, huge, free_pages);
> +       flush_tlb_kernel_range(start, end);
> +}
> +
> +static pte_t *merge_vmemmap_pte(pmd_t *pmdp, unsigned long addr)
> +{
> +       pte_t *pte;
> +       struct page *page;
> +
> +       pte = pte_offset_kernel(pmdp, addr);
> +       page = pte_page(*pte);
> +       set_pmd(pmdp, vmemmap_pmd_mkhuge(page));
> +
> +       return pte;
> +}
> +
> +static void merge_huge_page_pmd_vmemmap(pmd_t *pmd, unsigned long start,
> +                                       struct page *huge,
> +                                       struct list_head *free_pages)
> +{
> +       replace_huge_page_pmd_vmemmap(pmd, start, huge, free_pages);
> +       pte_free_kernel(&init_mm, merge_vmemmap_pte(pmd, start));
> +       flush_tlb_kernel_range(start, start + VMEMMAP_HPAGE_SIZE);
> +}
> +
>  static inline void alloc_vmemmap_pages(struct hstate *h, struct list_head *list)
>  {
>         int i;
> @@ -1772,6 +1828,15 @@ static inline void alloc_vmemmap_pages(struct hstate *h, struct list_head *list)
>         }
>  }
>
> +static inline void dissolve_compound_page(struct page *page, unsigned int order)
> +{
> +       int i;
> +       unsigned int nr_pages = 1 << order;
> +
> +       for (i = 1; i < nr_pages; i++)
> +               set_page_refcounted(page + i);
> +}
> +
>  static void alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
>  {
>         pmd_t *pmd;
> @@ -1791,10 +1856,45 @@ static void alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
>                                     __remap_huge_page_pte_vmemmap);
>         if (!freed_vmemmap_hpage_dec(pmd_page(*pmd)) && pmd_split(pmd)) {
>                 /*
> -                * Todo:
> -                * Merge pte to huge pmd if it has ever been split.
> +                * Merge pte to huge pmd if it has ever been split. Now only
> +                * support gigantic page which's vmemmap pages size is an
> +                * integer multiple of PMD_SIZE. This is the simplest case
> +                * to handle.
>                  */
>                 clear_pmd_split(pmd);
> +
> +               if (IS_ALIGNED(nr_vmemmap(h), VMEMMAP_HPAGE_NR)) {
> +                       unsigned long addr = (unsigned long)head;
> +                       unsigned long end = addr + nr_vmemmap_size(h);
> +
> +                       spin_unlock(ptl);
> +
> +                       for (; addr < end; addr += VMEMMAP_HPAGE_SIZE) {
> +                               void *to;
> +                               struct page *page;
> +
> +                               page = alloc_pages(GFP_VMEMMAP_PAGE & ~__GFP_NOFAIL,
> +                                                  VMEMMAP_HPAGE_ORDER);
> +                               if (!page)
> +                                       goto out;

Here forget to call dissolve_compound_page().

+                               dissolve_compound_page(page,
+                                                      VMEMMAP_HPAGE_ORDER);

> +
> +                               to = page_to_virt(page);
> +                               memcpy(to, (void *)addr, VMEMMAP_HPAGE_SIZE);
> +
> +                               /*
> +                                * Make sure that any data that writes to the
> +                                * @to is made visible to the physical page.
> +                                */
> +                               flush_kernel_vmap_range(to, VMEMMAP_HPAGE_SIZE);
> +
> +                               merge_huge_page_pmd_vmemmap(pmd++, addr, page,
> +                                                           &remap_pages);
> +                       }
> +
> +out:
> +                       free_vmemmap_page_list(&remap_pages);
> +                       return;
> +               }
>         }
>         spin_unlock(ptl);
>  }
> --
> 2.20.1
>


-- 
Yours,
Muchun


^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page
  2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
                   ` (24 preceding siblings ...)
  2020-09-15 14:32 ` [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Matthew Wilcox
@ 2020-09-29 21:58 ` Mike Kravetz
  2020-09-30  3:13   ` Matthew Wilcox
  2020-10-07 21:12   ` Mike Kravetz
  25 siblings, 2 replies; 48+ messages in thread
From: Mike Kravetz @ 2020-09-29 21:58 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel

On 9/15/20 5:59 AM, Muchun Song wrote:
> Hi all,
> 
> This patch series will free some vmemmap pages(struct page structures)
> associated with each hugetlbpage when preallocated to save memory.
...
> The mapping of the first page(index 0) and the second page(index 1) is
> unchanged. The remaining 6 pages are all mapped to the same page(index
> 1). So we only need 2 pages for vmemmap area and free 6 pages to the
> buddy system to save memory. Why we can do this? Because the content
> of the remaining 7 pages are usually same except the first page.
> 
> When a hugetlbpage is freed to the buddy system, we should allocate 6
> pages for vmemmap pages and restore the previous mapping relationship.
> 
> If we uses the 1G hugetlbpage, we can save 4095 pages. This is a very
> substantial gain. On our server, run some SPDK applications which will
> use 300GB hugetlbpage. With this feature enabled, we can save 4797MB
> memory.

At a high level this seems like a reasonable optimization for hugetlb
pages.  It is possible because hugetlb pages are 'special' and mostly
handled differently than pages in normal mm paths.

The majority of the new code is hugetlb specific, so it should not be
of too much concern for the general mm code paths.  I'll start looking
closer at the series.  However, if someone has high level concerns please
let us know.  The only 'potential' conflict I am aware of is discussion
about support of double mapping hugetlb pages.

https://lists.gnu.org/archive/html/qemu-devel/2017-03/msg02407.html

More care/coordination would be needed to support double mapping with
this new option.  However, this series provides a boot option to disable
freeing of unneeded page structs.
-- 
Mike Kravetz


^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [RFC PATCH 01/24] mm/memory_hotplug: Move bootmem info registration API to bootmem_info.c
  2020-09-15 12:59 ` [RFC PATCH 01/24] mm/memory_hotplug: Move bootmem info registration API to bootmem_info.c Muchun Song
@ 2020-09-29 22:46   ` Mike Kravetz
  0 siblings, 0 replies; 48+ messages in thread
From: Mike Kravetz @ 2020-09-29 22:46 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel

On 9/15/20 5:59 AM, Muchun Song wrote:
> Move bootmem info registration common API to individual bootmem_info.c
> for later patch use.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>

This is just code movement.

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

> ---
>  arch/x86/mm/init_64.c          |  1 +
>  include/linux/bootmem_info.h   | 27 ++++++++++
>  include/linux/memory_hotplug.h | 23 --------
>  mm/Makefile                    |  1 +
>  mm/bootmem_info.c              | 99 ++++++++++++++++++++++++++++++++++
>  mm/memory_hotplug.c            | 91 +------------------------------
>  6 files changed, 129 insertions(+), 113 deletions(-)
>  create mode 100644 include/linux/bootmem_info.h
>  create mode 100644 mm/bootmem_info.c


^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [RFC PATCH 02/24] mm/memory_hotplug: Move {get,put}_page_bootmem() to bootmem_info.c
  2020-09-15 12:59 ` [RFC PATCH 02/24] mm/memory_hotplug: Move {get,put}_page_bootmem() " Muchun Song
@ 2020-09-29 23:30   ` Mike Kravetz
  0 siblings, 0 replies; 48+ messages in thread
From: Mike Kravetz @ 2020-09-29 23:30 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel

On 9/15/20 5:59 AM, Muchun Song wrote:
> In the later patch, we will use {get,put}_page_bootmem() to initialize
> the page for vmemmap or free vmemmap page to buddy. So move them out of
> CONFIG_MEMORY_HOTPLUG_SPARSE.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>

More code movement.

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

> ---
>  arch/x86/mm/init_64.c          |  2 +-
>  include/linux/bootmem_info.h   | 13 +++++++++++++
>  include/linux/memory_hotplug.h |  4 ----
>  mm/bootmem_info.c              | 26 ++++++++++++++++++++++++++
>  mm/memory_hotplug.c            | 27 ---------------------------
>  mm/sparse.c                    |  1 +
>  6 files changed, 41 insertions(+), 32 deletions(-)


^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [RFC PATCH 03/24] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP
  2020-09-15 12:59 ` [RFC PATCH 03/24] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
  2020-09-16  2:13   ` Randy Dunlap
@ 2020-09-29 23:41   ` Mike Kravetz
  2020-09-30  2:56     ` [External] " Muchun Song
  1 sibling, 1 reply; 48+ messages in thread
From: Mike Kravetz @ 2020-09-29 23:41 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel

On 9/15/20 5:59 AM, Muchun Song wrote:
> The purpose of introducing HUGETLB_PAGE_FREE_VMEMMAP is to configure
> whether to enable the feature of freeing unused vmemmap associated
> with HugeTLB pages.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  fs/Kconfig | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/fs/Kconfig b/fs/Kconfig
> index 976e8b9033c4..61e9c08096ca 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -245,6 +245,21 @@ config HUGETLBFS
>  config HUGETLB_PAGE
>  	def_bool HUGETLBFS
>  
> +config HUGETLB_PAGE_FREE_VMEMMAP
> +	bool "Free unused vmemmap associated with HugeTLB pages"
> +	default n
> +	depends on HUGETLB_PAGE
> +	depends on SPARSEMEM_VMEMMAP
> +	depends on HAVE_BOOTMEM_INFO_NODE
> +	help
> +	  There are many struct page structure associated with each HugeTLB
> +	  page. But we only use a few struct page structure. In this case,
> +	  it waste some memory. It is better to free the unused struct page
> +	  structures to buddy system which can save some memory. For
> +	  architectures that support it, say Y here.
> +
> +	  If unsure, say N.
> +

I could be wrong, but I believe the convention is introduce the config
option at the same time code which depends on the option is introduced.
Therefore, it might be better to combine with the next patch.

Also, it looks like most of your development was done on x86.  Should
this option be limited to x86 only for now?
-- 
Mike Kravetz


^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [External] Re: [RFC PATCH 03/24] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP
  2020-09-29 23:41   ` Mike Kravetz
@ 2020-09-30  2:56     ` Muchun Song
  0 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-09-30  2:56 UTC (permalink / raw)
  To: Mike Kravetz
  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,
	linux-doc, LKML, Linux Memory Management List, linux-fsdevel

On Wed, Sep 30, 2020 at 7:41 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 9/15/20 5:59 AM, Muchun Song wrote:
> > The purpose of introducing HUGETLB_PAGE_FREE_VMEMMAP is to configure
> > whether to enable the feature of freeing unused vmemmap associated
> > with HugeTLB pages.
> >
> > Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> > ---
> >  fs/Kconfig | 15 +++++++++++++++
> >  1 file changed, 15 insertions(+)
> >
> > diff --git a/fs/Kconfig b/fs/Kconfig
> > index 976e8b9033c4..61e9c08096ca 100644
> > --- a/fs/Kconfig
> > +++ b/fs/Kconfig
> > @@ -245,6 +245,21 @@ config HUGETLBFS
> >  config HUGETLB_PAGE
> >       def_bool HUGETLBFS
> >
> > +config HUGETLB_PAGE_FREE_VMEMMAP
> > +     bool "Free unused vmemmap associated with HugeTLB pages"
> > +     default n
> > +     depends on HUGETLB_PAGE
> > +     depends on SPARSEMEM_VMEMMAP
> > +     depends on HAVE_BOOTMEM_INFO_NODE
> > +     help
> > +       There are many struct page structure associated with each HugeTLB
> > +       page. But we only use a few struct page structure. In this case,
> > +       it waste some memory. It is better to free the unused struct page
> > +       structures to buddy system which can save some memory. For
> > +       architectures that support it, say Y here.
> > +
> > +       If unsure, say N.
> > +
>
> I could be wrong, but I believe the convention is introduce the config
> option at the same time code which depends on the option is introduced.
> Therefore, it might be better to combine with the next patch.

Yeah, great. Will do that. Thanks.

>
> Also, it looks like most of your development was done on x86.  Should
> this option be limited to x86 only for now?

Now only the x86 has the HAVE_BOOTMEM_INFO_NODE option. So
maybe this is enough :)

> --
> Mike Kravetz



-- 
Yours,
Muchun


^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page
  2020-09-29 21:58 ` Mike Kravetz
@ 2020-09-30  3:13   ` Matthew Wilcox
  2020-10-07 21:12   ` Mike Kravetz
  1 sibling, 0 replies; 48+ messages in thread
From: Matthew Wilcox @ 2020-09-30  3:13 UTC (permalink / raw)
  To: Mike Kravetz
  Cc: 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, linux-doc, linux-kernel, linux-mm,
	linux-fsdevel

On Tue, Sep 29, 2020 at 02:58:18PM -0700, Mike Kravetz wrote:
> On 9/15/20 5:59 AM, Muchun Song wrote:
> > Hi all,
> > 
> > This patch series will free some vmemmap pages(struct page structures)
> > associated with each hugetlbpage when preallocated to save memory.
> ...
> > The mapping of the first page(index 0) and the second page(index 1) is
> > unchanged. The remaining 6 pages are all mapped to the same page(index
> > 1). So we only need 2 pages for vmemmap area and free 6 pages to the
> > buddy system to save memory. Why we can do this? Because the content
> > of the remaining 7 pages are usually same except the first page.
> > 
> > When a hugetlbpage is freed to the buddy system, we should allocate 6
> > pages for vmemmap pages and restore the previous mapping relationship.
> > 
> > If we uses the 1G hugetlbpage, we can save 4095 pages. This is a very
> > substantial gain. On our server, run some SPDK applications which will
> > use 300GB hugetlbpage. With this feature enabled, we can save 4797MB
> > memory.
> 
> At a high level this seems like a reasonable optimization for hugetlb
> pages.  It is possible because hugetlb pages are 'special' and mostly
> handled differently than pages in normal mm paths.
> 
> The majority of the new code is hugetlb specific, so it should not be
> of too much concern for the general mm code paths.  I'll start looking
> closer at the series.  However, if someone has high level concerns please
> let us know.  The only 'potential' conflict I am aware of is discussion
> about support of double mapping hugetlb pages.

Not on x86, but architectures which have dcache coherency issues sometimes
use PG_arch_1 on the subpages.  I think it would be wise to map pages
1-7 read-only to catch this, as well as any future change which causes
subpage bits to get set.


^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [RFC PATCH 05/24] mm/hugetlb: Introduce nr_free_vmemmap_pages in the struct hstate
  2020-09-15 12:59 ` [RFC PATCH 05/24] mm/hugetlb: Introduce nr_free_vmemmap_pages in the struct hstate Muchun Song
@ 2020-09-30 22:41   ` Mike Kravetz
  2020-10-01  2:57     ` [External] " Muchun Song
  0 siblings, 1 reply; 48+ messages in thread
From: Mike Kravetz @ 2020-09-30 22:41 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel

On 9/15/20 5:59 AM, Muchun Song wrote:
> If the size of hugetlb page is 2MB, we need 512 struct page structures
> (8 pages) to be associated with it. As far as I know, we only use the
> first 3 struct page structures and only read the compound_dtor members

Actually, the first 4 pages can be used if 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.
 */
#define HUGETLB_CGROUP_MIN_ORDER        2

However, this still easily fits within the first page of struct page
structures.

> of the remaining struct page structures. For tail page, the value of
> compound_dtor is the same. So we can reuse first tail page. We map the
> virtual addresses of the remaining 6 tail pages to the first tail page,
> and then free these 6 pages. Therefore, we need to reserve at least 2
> pages as vmemmap areas.

I got confused the first time I read the above sentences.  Perhaps it
should be more explicit with something like:

For tail pages, the value of compound_dtor is the same. So we can reuse
first page of tail page structs. We map the virtual addresses of the
remaining 6 pages of tail page structs to the first tail page struct,
and then free these 6 pages. Therefore, we need to reserve at least 2
pages as vmemmap areas.

It still does not sound great, but hopefully avoids some confusion.
-- 
Mike Kravetz

> So we introduce a new nr_free_vmemmap_pages field in the hstate to
> indicate how many vmemmap pages associated with a hugetlb page that we
> can free to buddy system.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  include/linux/hugetlb.h |  3 +++
>  mm/hugetlb.c            | 35 +++++++++++++++++++++++++++++++++++
>  2 files changed, 38 insertions(+)
> 
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index d5cc5f802dd4..eed3dd3bd626 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -492,6 +492,9 @@ 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 81a41aa080a5..f1b2b733b49b 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1292,6 +1292,39 @@ static inline void destroy_compound_gigantic_page(struct page *page,
>  						unsigned int order) { }
>  #endif
>  
> +#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
> +#define RESERVE_VMEMMAP_NR	2U
> +
> +static inline unsigned int nr_free_vmemmap(struct hstate *h)
> +{
> +	return h->nr_free_vmemmap_pages;
> +}
> +
> +static void __init hugetlb_vmemmap_init(struct hstate *h)
> +{
> +	unsigned int order = huge_page_order(h);
> +	unsigned int vmemmap_pages;
> +
> +	vmemmap_pages = ((1 << order) * sizeof(struct page)) >> PAGE_SHIFT;
> +	/*
> +	 * The head page and the first tail page not free to buddy system,
> +	 * the others page will map to the first tail page. So there are
> +	 * (@vmemmap_pages - RESERVE_VMEMMAP_NR) pages can be freed.
> +	 */
> +	if (vmemmap_pages > RESERVE_VMEMMAP_NR)
> +		h->nr_free_vmemmap_pages = vmemmap_pages - RESERVE_VMEMMAP_NR;
> +	else
> +		h->nr_free_vmemmap_pages = 0;
> +
> +	pr_info("HugeTLB: can free %d vmemmap pages for %s\n",
> +		h->nr_free_vmemmap_pages, h->name);
> +}
> +#else
> +static inline void hugetlb_vmemmap_init(struct hstate *h)
> +{
> +}
> +#endif
> +
>  static void update_and_free_page(struct hstate *h, struct page *page)
>  {
>  	int i;
> @@ -3285,6 +3318,8 @@ void __init hugetlb_add_hstate(unsigned int order)
>  	snprintf(h->name, HSTATE_NAME_LEN, "hugepages-%lukB",
>  					huge_page_size(h)/1024);
>  
> +	hugetlb_vmemmap_init(h);
> +
>  	parsed_hstate = h;
>  }
>  
> 


^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [External] Re: [RFC PATCH 05/24] mm/hugetlb: Introduce nr_free_vmemmap_pages in the struct hstate
  2020-09-30 22:41   ` Mike Kravetz
@ 2020-10-01  2:57     ` Muchun Song
  0 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-10-01  2:57 UTC (permalink / raw)
  To: Mike Kravetz
  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,
	linux-doc, LKML, Linux Memory Management List, linux-fsdevel

On Thu, Oct 1, 2020 at 6:41 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 9/15/20 5:59 AM, Muchun Song wrote:
> > If the size of hugetlb page is 2MB, we need 512 struct page structures
> > (8 pages) to be associated with it. As far as I know, we only use the
> > first 3 struct page structures and only read the compound_dtor members
>
> Actually, the first 4 pages can be used if CONFIG_CGROUP_HUGETLB.

Right, thanks.

> /*
>  * 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.
>  */
> #define HUGETLB_CGROUP_MIN_ORDER        2
>
> However, this still easily fits within the first page of struct page
> structures.
>
> > of the remaining struct page structures. For tail page, the value of
> > compound_dtor is the same. So we can reuse first tail page. We map the
> > virtual addresses of the remaining 6 tail pages to the first tail page,
> > and then free these 6 pages. Therefore, we need to reserve at least 2
> > pages as vmemmap areas.
>
> I got confused the first time I read the above sentences.  Perhaps it
> should be more explicit with something like:
>
> For tail pages, the value of compound_dtor is the same. So we can reuse
> first page of tail page structs. We map the virtual addresses of the
> remaining 6 pages of tail page structs to the first tail page struct,
> and then free these 6 pages. Therefore, we need to reserve at least 2
> pages as vmemmap areas.

Sorry for my poor English. Thanks for your suggestions. I can apply this.

>
> It still does not sound great, but hopefully avoids some confusion.
> --
> Mike Kravetz
>
> > So we introduce a new nr_free_vmemmap_pages field in the hstate to
> > indicate how many vmemmap pages associated with a hugetlb page that we
> > can free to buddy system.
> >
> > Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> > ---
> >  include/linux/hugetlb.h |  3 +++
> >  mm/hugetlb.c            | 35 +++++++++++++++++++++++++++++++++++
> >  2 files changed, 38 insertions(+)
> >
> > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> > index d5cc5f802dd4..eed3dd3bd626 100644
> > --- a/include/linux/hugetlb.h
> > +++ b/include/linux/hugetlb.h
> > @@ -492,6 +492,9 @@ 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 81a41aa080a5..f1b2b733b49b 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -1292,6 +1292,39 @@ static inline void destroy_compound_gigantic_page(struct page *page,
> >                                               unsigned int order) { }
> >  #endif
> >
> > +#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
> > +#define RESERVE_VMEMMAP_NR   2U
> > +
> > +static inline unsigned int nr_free_vmemmap(struct hstate *h)
> > +{
> > +     return h->nr_free_vmemmap_pages;
> > +}
> > +
> > +static void __init hugetlb_vmemmap_init(struct hstate *h)
> > +{
> > +     unsigned int order = huge_page_order(h);
> > +     unsigned int vmemmap_pages;
> > +
> > +     vmemmap_pages = ((1 << order) * sizeof(struct page)) >> PAGE_SHIFT;
> > +     /*
> > +      * The head page and the first tail page not free to buddy system,
> > +      * the others page will map to the first tail page. So there are
> > +      * (@vmemmap_pages - RESERVE_VMEMMAP_NR) pages can be freed.
> > +      */
> > +     if (vmemmap_pages > RESERVE_VMEMMAP_NR)
> > +             h->nr_free_vmemmap_pages = vmemmap_pages - RESERVE_VMEMMAP_NR;
> > +     else
> > +             h->nr_free_vmemmap_pages = 0;
> > +
> > +     pr_info("HugeTLB: can free %d vmemmap pages for %s\n",
> > +             h->nr_free_vmemmap_pages, h->name);
> > +}
> > +#else
> > +static inline void hugetlb_vmemmap_init(struct hstate *h)
> > +{
> > +}
> > +#endif
> > +
> >  static void update_and_free_page(struct hstate *h, struct page *page)
> >  {
> >       int i;
> > @@ -3285,6 +3318,8 @@ void __init hugetlb_add_hstate(unsigned int order)
> >       snprintf(h->name, HSTATE_NAME_LEN, "hugepages-%lukB",
> >                                       huge_page_size(h)/1024);
> >
> > +     hugetlb_vmemmap_init(h);
> > +
> >       parsed_hstate = h;
> >  }
> >
> >



-- 
Yours,
Muchun


^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page
  2020-09-29 21:58 ` Mike Kravetz
  2020-09-30  3:13   ` Matthew Wilcox
@ 2020-10-07 21:12   ` Mike Kravetz
  2020-10-09  4:13     ` [External] " Muchun Song
  1 sibling, 1 reply; 48+ messages in thread
From: Mike Kravetz @ 2020-10-07 21:12 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
  Cc: linux-doc, linux-kernel, linux-mm, linux-fsdevel

On 9/29/20 2:58 PM, Mike Kravetz wrote:
> On 9/15/20 5:59 AM, Muchun Song wrote:
>> Hi all,
>>
>> This patch series will free some vmemmap pages(struct page structures)
>> associated with each hugetlbpage when preallocated to save memory.
> ...
>> The mapping of the first page(index 0) and the second page(index 1) is
>> unchanged. The remaining 6 pages are all mapped to the same page(index
>> 1). So we only need 2 pages for vmemmap area and free 6 pages to the
>> buddy system to save memory. Why we can do this? Because the content
>> of the remaining 7 pages are usually same except the first page.
>>
>> When a hugetlbpage is freed to the buddy system, we should allocate 6
>> pages for vmemmap pages and restore the previous mapping relationship.
>>
>> If we uses the 1G hugetlbpage, we can save 4095 pages. This is a very
>> substantial gain. On our server, run some SPDK applications which will
>> use 300GB hugetlbpage. With this feature enabled, we can save 4797MB
>> memory.

I had a hard time going through the patch series as it is currently
structured, and instead examined all the code together.  Muchun put in
much effort and the code does reduce memory usage.
- For 2MB hugetlb pages, we save 5 pages of struct pages
- For 1GB hugetlb pages, we save 4086 pages of struct pages

Code is even in pace to handle poisoned pages, although I have not looked
at this closely.  The code survives the libhugetlbfs and ltp huge page tests.

To date, nobody has asked the important question "Is the added complexity
worth the memory savings?".  I suppose it all depends on one's use case.
Obviously, the savings are more significant when one uses 1G huge pages but
that may not be the common case today.

> At a high level this seems like a reasonable optimization for hugetlb
> pages.  It is possible because hugetlb pages are 'special' and mostly
> handled differently than pages in normal mm paths.

Such an optimization only makes sense for something like hugetlb pages.  One
reason is the 'special' nature of hugetlbfs as stated above.  The other is
that this optimization mostly makes sense for huge pages that are created
once and stick around for a long time.  hugetlb pool pages are a perfect
example.  This is because manipulation of struct page mappings is done when
a huge page is created or destroyed.

> The majority of the new code is hugetlb specific, so it should not be
> of too much concern for the general mm code paths.

It is true that much of the code in this series was put in hugetlb.c.  However,
I would argue that there is a bunch of code that only deals with remapping
the memmap which should more generic and added to sparse-vmemmap.c.  This
would at least allow for easier reuse.

Before Muchun and myself put more effort into this series, I would really
like to get feedback on the whether or not this should move forward.
Specifically, is the memory savings worth added complexity?  Is the removing
of struct pages going to come back and cause issues for future features?
-- 
Mike Kravetz


^ permalink raw reply	[flat|nested] 48+ messages in thread

* Re: [External] Re: [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page
  2020-10-07 21:12   ` Mike Kravetz
@ 2020-10-09  4:13     ` Muchun Song
  0 siblings, 0 replies; 48+ messages in thread
From: Muchun Song @ 2020-10-09  4:13 UTC (permalink / raw)
  To: Mike Kravetz
  Cc: Jonathan Corbet, Thomas Gleixner, mingo, bp, x86, hpa,
	dave.hansen, luto, Peter Zijlstra, viro, Andrew Morton, paulmck,
	mchehab+huawei, pawan.kumar.gupta, Matthew Wilcox, Randy Dunlap,
	oneukum, anshuman.khandual, jroedel, Mina Almasry,
	David Rientjes, linux-doc, LKML, Linux Memory Management List,
	linux-fsdevel, Xiongchun duan

On Thu, Oct 8, 2020 at 5:15 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 9/29/20 2:58 PM, Mike Kravetz wrote:
> > On 9/15/20 5:59 AM, Muchun Song wrote:
> >> Hi all,
> >>
> >> This patch series will free some vmemmap pages(struct page structures)
> >> associated with each hugetlbpage when preallocated to save memory.
> > ...
> >> The mapping of the first page(index 0) and the second page(index 1) is
> >> unchanged. The remaining 6 pages are all mapped to the same page(index
> >> 1). So we only need 2 pages for vmemmap area and free 6 pages to the
> >> buddy system to save memory. Why we can do this? Because the content
> >> of the remaining 7 pages are usually same except the first page.
> >>
> >> When a hugetlbpage is freed to the buddy system, we should allocate 6
> >> pages for vmemmap pages and restore the previous mapping relationship.
> >>
> >> If we uses the 1G hugetlbpage, we can save 4095 pages. This is a very
> >> substantial gain. On our server, run some SPDK applications which will
> >> use 300GB hugetlbpage. With this feature enabled, we can save 4797MB
> >> memory.
>
> I had a hard time going through the patch series as it is currently
> structured, and instead examined all the code together.  Muchun put in
> much effort and the code does reduce memory usage.
> - For 2MB hugetlb pages, we save 5 pages of struct pages
> - For 1GB hugetlb pages, we save 4086 pages of struct pages
>
> Code is even in pace to handle poisoned pages, although I have not looked
> at this closely.  The code survives the libhugetlbfs and ltp huge page tests.
>
> To date, nobody has asked the important question "Is the added complexity
> worth the memory savings?".  I suppose it all depends on one's use case.
> Obviously, the savings are more significant when one uses 1G huge pages but
> that may not be the common case today.
>
> > At a high level this seems like a reasonable optimization for hugetlb
> > pages.  It is possible because hugetlb pages are 'special' and mostly
> > handled differently than pages in normal mm paths.
>
> Such an optimization only makes sense for something like hugetlb pages.  One
> reason is the 'special' nature of hugetlbfs as stated above.  The other is
> that this optimization mostly makes sense for huge pages that are created
> once and stick around for a long time.  hugetlb pool pages are a perfect
> example.  This is because manipulation of struct page mappings is done when
> a huge page is created or destroyed.

Yeah, in our cloud server, we have some application scenarios(e.g. SPDK,
DPDK, QEMU and jemalloc). These applications may use a lot of hugetlb
pages.

>
> > The majority of the new code is hugetlb specific, so it should not be
> > of too much concern for the general mm code paths.
>
> It is true that much of the code in this series was put in hugetlb.c.  However,
> I would argue that there is a bunch of code that only deals with remapping
> the memmap which should more generic and added to sparse-vmemmap.c.  This
> would at least allow for easier reuse.

I agree with you.

>
> Before Muchun and myself put more effort into this series, I would really
> like to get feedback on the whether or not this should move forward.
> Specifically, is the memory savings worth added complexity?  Is the removing
> of struct pages going to come back and cause issues for future features?

Some users do need this optimization to save memory. But if some users
do not need this optimization, they also can disable it by using a kernel boot
parameter 'hugetlb_free_vmemmap=off' or not configuring
CONFIG_HUGETLB_PAGE_FREE_VMEMMAP.

I have no idea about "cause issues for future features". Is there any feature
ongoing or planned?

-- 
Yours,
Muchun


^ permalink raw reply	[flat|nested] 48+ messages in thread

end of thread, other threads:[~2020-10-09  4:14 UTC | newest]

Thread overview: 48+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
2020-09-15 12:59 ` [RFC PATCH 01/24] mm/memory_hotplug: Move bootmem info registration API to bootmem_info.c Muchun Song
2020-09-29 22:46   ` Mike Kravetz
2020-09-15 12:59 ` [RFC PATCH 02/24] mm/memory_hotplug: Move {get,put}_page_bootmem() " Muchun Song
2020-09-29 23:30   ` Mike Kravetz
2020-09-15 12:59 ` [RFC PATCH 03/24] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
2020-09-16  2:13   ` Randy Dunlap
2020-09-29 23:41   ` Mike Kravetz
2020-09-30  2:56     ` [External] " Muchun Song
2020-09-15 12:59 ` [RFC PATCH 04/24] mm/hugetlb: Register bootmem info when CONFIG_HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
2020-09-15 12:59 ` [RFC PATCH 05/24] mm/hugetlb: Introduce nr_free_vmemmap_pages in the struct hstate Muchun Song
2020-09-30 22:41   ` Mike Kravetz
2020-10-01  2:57     ` [External] " Muchun Song
2020-09-15 12:59 ` [RFC PATCH 06/24] mm/hugetlb: Introduce pgtable allocation/freeing helpers Muchun Song
2020-09-15 12:59 ` [RFC PATCH 07/24] mm/hugetlb: Add freeing unused vmemmap pages support for x86 Muchun Song
2020-09-15 12:59 ` [RFC PATCH 08/24] mm/bootmem_info: Introduce {free,prepare}_vmemmap_page() Muchun Song
2020-09-15 12:59 ` [RFC PATCH 09/24] x86/mm: Introduce VMEMMAP_SIZE/VMEMMAP_END macro Muchun Song
2020-09-15 12:59 ` [RFC PATCH 10/24] mm/hugetlb: Free the vmemmap pages associated with each hugetlb page Muchun Song
2020-09-15 12:59 ` [RFC PATCH 11/24] mm/hugetlb: Add vmemmap_pmd_huge macro for x86 Muchun Song
2020-09-15 12:59 ` [RFC PATCH 12/24] mm/hugetlb: Defer freeing of hugetlb pages Muchun Song
2020-09-15 12:59 ` [RFC PATCH 13/24] mm/hugetlb: Allocate the vmemmap pages associated with each hugetlb page Muchun Song
2020-09-15 12:59 ` [RFC PATCH 14/24] mm/hugetlb: Introduce remap_huge_page_pmd_vmemmap helper Muchun Song
2020-09-15 12:59 ` [RFC PATCH 15/24] mm/hugetlb: Use PG_slab to indicate split pmd Muchun Song
2020-09-15 12:59 ` [RFC PATCH 16/24] mm/hugetlb: Support freeing vmemmap pages of gigantic page Muchun Song
2020-09-15 12:59 ` [RFC PATCH 17/24] mm/hugetlb: Add a BUILD_BUG_ON to check if struct page size is a power of two Muchun Song
2020-09-15 12:59 ` [RFC PATCH 18/24] mm/hugetlb: Clear PageHWPoison on the non-error memory page Muchun Song
2020-09-15 12:59 ` [RFC PATCH 19/24] mm/hugetlb: Flush work when dissolving hugetlb page Muchun Song
2020-09-15 12:59 ` [RFC PATCH 20/24] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap Muchun Song
2020-09-16  2:10   ` Randy Dunlap
2020-09-16  2:50     ` [External] " Muchun Song
2020-09-15 12:59 ` [RFC PATCH 21/24] mm/hugetlb: Merge pte to huge pmd only for gigantic page Muchun Song
2020-09-20  9:59   ` Muchun Song
2020-09-15 12:59 ` [RFC PATCH 22/24] mm/hugetlb: Implement vmemmap_pmd_mkhuge macro Muchun Song
2020-09-15 12:59 ` [RFC PATCH 23/24] mm/hugetlb: Gather discrete indexes of tail page Muchun Song
2020-09-15 12:59 ` [RFC PATCH 24/24] mm/hugetlb: Add BUILD_BUG_ON to catch invalid usage of tail struct page Muchun Song
2020-09-15 14:32 ` [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Matthew Wilcox
2020-09-15 14:53   ` Dave Hansen
2020-09-15 15:28   ` [External] " Muchun Song
2020-09-15 15:42     ` Matthew Wilcox
2020-09-15 17:32       ` Muchun Song
2020-09-15 17:39         ` Matthew Wilcox
2020-09-15 18:03           ` Muchun Song
2020-09-15 18:15             ` Matthew Wilcox
2020-09-16  2:45               ` Muchun Song
2020-09-29 21:58 ` Mike Kravetz
2020-09-30  3:13   ` Matthew Wilcox
2020-10-07 21:12   ` Mike Kravetz
2020-10-09  4:13     ` [External] " Muchun Song

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