[PATCH v4 0/4] Record additional page allocation reasons

[PATCH v4 0/4] Record additional page allocation reasons

[Matthew Wilcox]

From: Matthew Wilcox <mawilcox@microsoft.com>

Rework how the _map_count field in struct page is used to record why
the page was allocated.  We now have about twenty bits available, and
I've taken two of them to mark pages allocated for page tables and
through vmalloc.  They are reported by the page-types tool as g and
V respectively.

Changes since v3:
 - Ack from Martin on s390 changes
 - Fix up some comments
 - Removed check for PageType from fs/proc/page.c; page_mapped() handles
   this just fine.
 - Added KPF_VMALLOC and KPF_PGTABLE (hence cc'ing linux-api)
 - Set KPF_VMALLOC and KPF_PGTABLE in fs/proc/page.c
 - Interpret KPF_VMALLOC and KPF_PGTABLE in tools/vm/page-flags.c
 - Set PageTable on tile's extra pages

Matthew Wilcox (4):
  s390: Use _refcount for pgtables
  mm: Split page_type out from _map_count
  mm: Mark pages allocated through vmalloc
  mm: Mark pages in use for page tables

 arch/s390/mm/pgalloc.c                 | 21 +++++++------
 arch/tile/mm/pgtable.c                 |  3 ++
 fs/proc/page.c                         |  4 +++
 include/linux/mm.h                     |  2 ++
 include/linux/mm_types.h               | 13 +++++---
 include/linux/page-flags.h             | 57 ++++++++++++++++++++++------------
 include/uapi/linux/kernel-page-flags.h |  3 +-
 kernel/crash_core.c                    |  1 +
 mm/page_alloc.c                        | 13 +++-----
 mm/vmalloc.c                           |  2 ++
 scripts/tags.sh                        |  6 ++--
 tools/vm/page-types.c                  |  2 ++
 12 files changed, 82 insertions(+), 45 deletions(-)

-- 
2.16.1

[PATCH v4 1/4] s390: Use _refcount for pgtables

[Matthew Wilcox]

From: Matthew Wilcox <mawilcox@microsoft.com>

s390 borrows the storage used for _mapcount in struct page in order to
account whether the bottom or top half is being used for 2kB page
tables.  I want to use that for something else, so use the top byte of
_refcount instead of the bottom byte of _mapcount.  _refcount may
temporarily be incremented by other CPUs that see a stale pointer to
this page in the page cache, but each CPU can only increment it by one,
and there are no systems with 2^24 CPUs today, so they will not change
the upper byte of _refcount.  We do have to be a little careful not to
lose any of their writes (as they will subsequently decrement the
counter).

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---
 arch/s390/mm/pgalloc.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c
index cb364153c43c..412c5f48a8e7 100644
--- a/arch/s390/mm/pgalloc.c
+++ b/arch/s390/mm/pgalloc.c
@@ -189,14 +189,15 @@ unsigned long *page_table_alloc(struct mm_struct *mm)
 		if (!list_empty(&mm->context.pgtable_list)) {
 			page = list_first_entry(&mm->context.pgtable_list,
 						struct page, lru);
-			mask = atomic_read(&page->_mapcount);
+			mask = atomic_read(&page->_refcount) >> 24;
 			mask = (mask | (mask >> 4)) & 3;
 			if (mask != 3) {
 				table = (unsigned long *) page_to_phys(page);
 				bit = mask & 1;		/* =1 -> second 2K */
 				if (bit)
 					table += PTRS_PER_PTE;
-				atomic_xor_bits(&page->_mapcount, 1U << bit);
+				atomic_xor_bits(&page->_refcount,
+							1U << (bit + 24));
 				list_del(&page->lru);
 			}
 		}
@@ -217,12 +218,12 @@ unsigned long *page_table_alloc(struct mm_struct *mm)
 	table = (unsigned long *) page_to_phys(page);
 	if (mm_alloc_pgste(mm)) {
 		/* Return 4K page table with PGSTEs */
-		atomic_set(&page->_mapcount, 3);
+		atomic_xor_bits(&page->_refcount, 3 << 24);
 		memset64((u64 *)table, _PAGE_INVALID, PTRS_PER_PTE);
 		memset64((u64 *)table + PTRS_PER_PTE, 0, PTRS_PER_PTE);
 	} else {
 		/* Return the first 2K fragment of the page */
-		atomic_set(&page->_mapcount, 1);
+		atomic_xor_bits(&page->_refcount, 1 << 24);
 		memset64((u64 *)table, _PAGE_INVALID, 2 * PTRS_PER_PTE);
 		spin_lock_bh(&mm->context.lock);
 		list_add(&page->lru, &mm->context.pgtable_list);
@@ -241,7 +242,8 @@ void page_table_free(struct mm_struct *mm, unsigned long *table)
 		/* Free 2K page table fragment of a 4K page */
 		bit = (__pa(table) & ~PAGE_MASK)/(PTRS_PER_PTE*sizeof(pte_t));
 		spin_lock_bh(&mm->context.lock);
-		mask = atomic_xor_bits(&page->_mapcount, 1U << bit);
+		mask = atomic_xor_bits(&page->_refcount, 1U << (bit + 24));
+		mask >>= 24;
 		if (mask & 3)
 			list_add(&page->lru, &mm->context.pgtable_list);
 		else
@@ -252,7 +254,6 @@ void page_table_free(struct mm_struct *mm, unsigned long *table)
 	}
 
 	pgtable_page_dtor(page);
-	atomic_set(&page->_mapcount, -1);
 	__free_page(page);
 }
 
@@ -273,7 +274,8 @@ void page_table_free_rcu(struct mmu_gather *tlb, unsigned long *table,
 	}
 	bit = (__pa(table) & ~PAGE_MASK) / (PTRS_PER_PTE*sizeof(pte_t));
 	spin_lock_bh(&mm->context.lock);
-	mask = atomic_xor_bits(&page->_mapcount, 0x11U << bit);
+	mask = atomic_xor_bits(&page->_refcount, 0x11U << (bit + 24));
+	mask >>= 24;
 	if (mask & 3)
 		list_add_tail(&page->lru, &mm->context.pgtable_list);
 	else
@@ -295,12 +297,13 @@ static void __tlb_remove_table(void *_table)
 		break;
 	case 1:		/* lower 2K of a 4K page table */
 	case 2:		/* higher 2K of a 4K page table */
-		if (atomic_xor_bits(&page->_mapcount, mask << 4) != 0)
+		mask = atomic_xor_bits(&page->_refcount, mask << (4 + 24));
+		mask >>= 24;
+		if (mask != 0)
 			break;
 		/* fallthrough */
 	case 3:		/* 4K page table with pgstes */
 		pgtable_page_dtor(page);
-		atomic_set(&page->_mapcount, -1);
 		__free_page(page);
 		break;
 	}
-- 
2.16.1

[PATCH v4 2/4] mm: Split page_type out from _map_count

[Matthew Wilcox]

From: Matthew Wilcox <mawilcox@microsoft.com>

We're already using a union of many fields here, so stop abusing the
_map_count and make page_type its own field.  That implies renaming some
of the machinery that creates PageBuddy, PageBalloon and PageKmemcg;
bring back the PG_buddy, PG_balloon and PG_kmemcg names.

As suggested by Kirill, make page_type a bitmask.  Because it starts out
life as -1 (thanks to sharing the storage with _map_count), setting a
page flag means clearing the appropriate bit.  This gives us space for
probably twenty or so extra bits (depending how paranoid we want to be
about _mapcount underflow).

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
---
 include/linux/mm_types.h   | 13 ++++++++-----
 include/linux/page-flags.h | 45 ++++++++++++++++++++++++++-------------------
 kernel/crash_core.c        |  1 +
 mm/page_alloc.c            | 13 +++++--------
 scripts/tags.sh            |  6 +++---
 5 files changed, 43 insertions(+), 35 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index fd1af6b9591d..1c5dea402501 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -94,6 +94,14 @@ struct page {
 	};
 
 	union {
+		/*
+		 * If the page is neither PageSlab nor PageAnon, the value
+		 * stored here may help distinguish it from page cache pages.
+		 * See page-flags.h for a list of page types which are
+		 * currently stored here.
+		 */
+		unsigned int page_type;
+
 		_slub_counter_t counters;
 		unsigned int active;		/* SLAB */
 		struct {			/* SLUB */
@@ -107,11 +115,6 @@ struct page {
 			/*
 			 * Count of ptes mapped in mms, to show when
 			 * page is mapped & limit reverse map searches.
-			 *
-			 * Extra information about page type may be
-			 * stored here for pages that are never mapped,
-			 * in which case the value MUST BE <= -2.
-			 * See page-flags.h for more details.
 			 */
 			atomic_t _mapcount;
 
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 50c2b8786831..d151f590bbc6 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -630,49 +630,56 @@ PAGEFLAG_FALSE(DoubleMap)
 #endif
 
 /*
- * For pages that are never mapped to userspace, page->mapcount may be
- * used for storing extra information about page type. Any value used
- * for this purpose must be <= -2, but it's better start not too close
- * to -2 so that an underflow of the page_mapcount() won't be mistaken
- * for a special page.
+ * For pages that are never mapped to userspace (and aren't PageSlab),
+ * page_type may be used.  Because it is initialised to -1, we invert the
+ * sense of the bit, so __SetPageFoo *clears* the bit used for PageFoo, and
+ * __ClearPageFoo *sets* the bit used for PageFoo.  We leave a gap in the bit
+ * assignments so that an underflow of page_mapcount() won't be mistaken for
+ * a special page.
  */
-#define PAGE_MAPCOUNT_OPS(uname, lname)					\
+
+#define PAGE_TYPE_BASE	0xff000000
+/* Reserve		0x0000007f to catch underflows of page_mapcount */
+#define PG_buddy	0x00000080
+#define PG_balloon	0x00000100
+#define PG_kmemcg	0x00000200
+
+#define PageType(page, flag)						\
+	((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE)
+
+#define PAGE_TYPE_OPS(uname, lname)					\
 static __always_inline int Page##uname(struct page *page)		\
 {									\
-	return atomic_read(&page->_mapcount) ==				\
-				PAGE_##lname##_MAPCOUNT_VALUE;		\
+	return PageType(page, PG_##lname);				\
 }									\
 static __always_inline void __SetPage##uname(struct page *page)		\
 {									\
-	VM_BUG_ON_PAGE(atomic_read(&page->_mapcount) != -1, page);	\
-	atomic_set(&page->_mapcount, PAGE_##lname##_MAPCOUNT_VALUE);	\
+	VM_BUG_ON_PAGE(!PageType(page, 0), page);			\
+	page->page_type &= ~PG_##lname;					\
 }									\
 static __always_inline void __ClearPage##uname(struct page *page)	\
 {									\
 	VM_BUG_ON_PAGE(!Page##uname(page), page);			\
-	atomic_set(&page->_mapcount, -1);				\
+	page->page_type |= PG_##lname;					\
 }
 
 /*
- * PageBuddy() indicate that the page is free and in the buddy system
+ * PageBuddy() indicates that the page is free and in the buddy system
  * (see mm/page_alloc.c).
  */
-#define PAGE_BUDDY_MAPCOUNT_VALUE		(-128)
-PAGE_MAPCOUNT_OPS(Buddy, BUDDY)
+PAGE_TYPE_OPS(Buddy, buddy)
 
 /*
- * PageBalloon() is set on pages that are on the balloon page list
+ * PageBalloon() is true for pages that are on the balloon page list
  * (see mm/balloon_compaction.c).
  */
-#define PAGE_BALLOON_MAPCOUNT_VALUE		(-256)
-PAGE_MAPCOUNT_OPS(Balloon, BALLOON)
+PAGE_TYPE_OPS(Balloon, balloon)
 
 /*
  * If kmemcg is enabled, the buddy allocator will set PageKmemcg() on
  * pages allocated with __GFP_ACCOUNT. It gets cleared on page free.
  */
-#define PAGE_KMEMCG_MAPCOUNT_VALUE		(-512)
-PAGE_MAPCOUNT_OPS(Kmemcg, KMEMCG)
+PAGE_TYPE_OPS(Kmemcg, kmemcg)
 
 extern bool is_free_buddy_page(struct page *page);
 
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 4f63597c824d..b02340fb99ff 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -458,6 +458,7 @@ static int __init crash_save_vmcoreinfo_init(void)
 	VMCOREINFO_NUMBER(PG_hwpoison);
 #endif
 	VMCOREINFO_NUMBER(PG_head_mask);
+#define PAGE_BUDDY_MAPCOUNT_VALUE	(~PG_buddy)
 	VMCOREINFO_NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE);
 #ifdef CONFIG_HUGETLB_PAGE
 	VMCOREINFO_NUMBER(HUGETLB_PAGE_DTOR);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cb416723538f..ac0b24603030 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -744,16 +744,14 @@ static inline void rmv_page_order(struct page *page)
 
 /*
  * This function checks whether a page is free && is the buddy
- * we can do coalesce a page and its buddy if
+ * we can coalesce a page and its buddy if
  * (a) the buddy is not in a hole (check before calling!) &&
  * (b) the buddy is in the buddy system &&
  * (c) a page and its buddy have the same order &&
  * (d) a page and its buddy are in the same zone.
  *
- * For recording whether a page is in the buddy system, we set ->_mapcount
- * PAGE_BUDDY_MAPCOUNT_VALUE.
- * Setting, clearing, and testing _mapcount PAGE_BUDDY_MAPCOUNT_VALUE is
- * serialized by zone->lock.
+ * For recording whether a page is in the buddy system, we set PageBuddy.
+ * Setting, clearing, and testing PageBuddy is serialized by zone->lock.
  *
  * For recording page's order, we use page_private(page).
  */
@@ -798,9 +796,8 @@ static inline int page_is_buddy(struct page *page, struct page *buddy,
  * as necessary, plus some accounting needed to play nicely with other
  * parts of the VM system.
  * At each level, we keep a list of pages, which are heads of continuous
- * free pages of length of (1 << order) and marked with _mapcount
- * PAGE_BUDDY_MAPCOUNT_VALUE. Page's order is recorded in page_private(page)
- * field.
+ * free pages of length of (1 << order) and marked with PageBuddy.
+ * Page's order is recorded in page_private(page) field.
  * So when we are allocating or freeing one, we can derive the state of the
  * other.  That is, if we allocate a small block, and both were
  * free, the remainder of the region must be split into blocks.
diff --git a/scripts/tags.sh b/scripts/tags.sh
index 78e546ff689c..8c3ae36d4ea8 100755
--- a/scripts/tags.sh
+++ b/scripts/tags.sh
@@ -188,9 +188,9 @@ regex_c=(
 	'/\<CLEARPAGEFLAG_NOOP(\([[:alnum:]_]*\).*/ClearPage\1/'
 	'/\<__CLEARPAGEFLAG_NOOP(\([[:alnum:]_]*\).*/__ClearPage\1/'
 	'/\<TESTCLEARFLAG_FALSE(\([[:alnum:]_]*\).*/TestClearPage\1/'
-	'/^PAGE_MAPCOUNT_OPS(\([[:alnum:]_]*\).*/Page\1/'
-	'/^PAGE_MAPCOUNT_OPS(\([[:alnum:]_]*\).*/__SetPage\1/'
-	'/^PAGE_MAPCOUNT_OPS(\([[:alnum:]_]*\).*/__ClearPage\1/'
+	'/^PAGE_TYPE_OPS(\([[:alnum:]_]*\).*/Page\1/'
+	'/^PAGE_TYPE_OPS(\([[:alnum:]_]*\).*/__SetPage\1/'
+	'/^PAGE_TYPE_OPS(\([[:alnum:]_]*\).*/__ClearPage\1/'
 	'/^TASK_PFA_TEST([^,]*, *\([[:alnum:]_]*\))/task_\1/'
 	'/^TASK_PFA_SET([^,]*, *\([[:alnum:]_]*\))/task_set_\1/'
 	'/^TASK_PFA_CLEAR([^,]*, *\([[:alnum:]_]*\))/task_clear_\1/'
-- 
2.16.1

[PATCH v4 3/4] mm: Mark pages allocated through vmalloc

[Matthew Wilcox]

From: Matthew Wilcox <mawilcox@microsoft.com>

Use a bit in page_type to mark pages which have been allocated through
vmalloc.  This can be helpful when debugging crashdumps or analysing
memory fragmentation.  Add a KPF flag to report these pages to userspace
and update page-types.c to interpret that flag.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
---
 fs/proc/page.c                         | 2 ++
 include/linux/page-flags.h             | 6 ++++++
 include/uapi/linux/kernel-page-flags.h | 2 +-
 mm/vmalloc.c                           | 2 ++
 tools/vm/page-types.c                  | 1 +
 5 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/fs/proc/page.c b/fs/proc/page.c
index 1491918a33c3..c9757af919a3 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -154,6 +154,8 @@ u64 stable_page_flags(struct page *page)
 
 	if (PageBalloon(page))
 		u |= 1 << KPF_BALLOON;
+	if (PageVmalloc(page))
+		u |= 1 << KPF_VMALLOC;
 
 	if (page_is_idle(page))
 		u |= 1 << KPF_IDLE;
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index d151f590bbc6..8142ab716e90 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -643,6 +643,7 @@ PAGEFLAG_FALSE(DoubleMap)
 #define PG_buddy	0x00000080
 #define PG_balloon	0x00000100
 #define PG_kmemcg	0x00000200
+#define PG_vmalloc	0x00000400
 
 #define PageType(page, flag)						\
 	((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE)
@@ -681,6 +682,11 @@ PAGE_TYPE_OPS(Balloon, balloon)
  */
 PAGE_TYPE_OPS(Kmemcg, kmemcg)
 
+/*
+ * Pages allocated through vmalloc are tagged with this bit.
+ */
+PAGE_TYPE_OPS(Vmalloc, vmalloc)
+
 extern bool is_free_buddy_page(struct page *page);
 
 __PAGEFLAG(Isolated, isolated, PF_ANY);
diff --git a/include/uapi/linux/kernel-page-flags.h b/include/uapi/linux/kernel-page-flags.h
index fa139841ec18..5f1735ff05b3 100644
--- a/include/uapi/linux/kernel-page-flags.h
+++ b/include/uapi/linux/kernel-page-flags.h
@@ -35,6 +35,6 @@
 #define KPF_BALLOON		23
 #define KPF_ZERO_PAGE		24
 #define KPF_IDLE		25
-
+#define KPF_VMALLOC		26
 
 #endif /* _UAPILINUX_KERNEL_PAGE_FLAGS_H */
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index ebff729cc956..3bc0538fc21b 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1536,6 +1536,7 @@ static void __vunmap(const void *addr, int deallocate_pages)
 			struct page *page = area->pages[i];
 
 			BUG_ON(!page);
+			__ClearPageVmalloc(page);
 			__free_pages(page, 0);
 		}
 
@@ -1705,6 +1706,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 			area->nr_pages = i;
 			goto fail;
 		}
+		__SetPageVmalloc(page);
 		area->pages[i] = page;
 		if (gfpflags_allow_blocking(gfp_mask|highmem_mask))
 			cond_resched();
diff --git a/tools/vm/page-types.c b/tools/vm/page-types.c
index a8783f48f77f..116f59eff5e2 100644
--- a/tools/vm/page-types.c
+++ b/tools/vm/page-types.c
@@ -131,6 +131,7 @@ static const char * const page_flag_names[] = {
 	[KPF_KSM]		= "x:ksm",
 	[KPF_THP]		= "t:thp",
 	[KPF_BALLOON]		= "o:balloon",
+	[KPF_VMALLOC]		= "V:vmalloc",
 	[KPF_ZERO_PAGE]		= "z:zero_page",
 	[KPF_IDLE]              = "i:idle_page",
 
-- 
2.16.1

[PATCH v4 4/4] mm: Mark pages in use for page tables

[Matthew Wilcox]

From: Matthew Wilcox <mawilcox@microsoft.com>

Define a new PageTable bit in the page_type and use it to mark pages in
use as page tables.  This can be helpful when debugging crashdumps or
analysing memory fragmentation.  Add a KPF flag to report these pages
to userspace and update page-types.c to interpret that flag.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
---
 arch/tile/mm/pgtable.c                 | 3 +++
 fs/proc/page.c                         | 2 ++
 include/linux/mm.h                     | 2 ++
 include/linux/page-flags.h             | 6 ++++++
 include/uapi/linux/kernel-page-flags.h | 1 +
 tools/vm/page-types.c                  | 1 +
 6 files changed, 15 insertions(+)

diff --git a/arch/tile/mm/pgtable.c b/arch/tile/mm/pgtable.c
index ec5576fd3a86..6dff12db335d 100644
--- a/arch/tile/mm/pgtable.c
+++ b/arch/tile/mm/pgtable.c
@@ -206,6 +206,7 @@ struct page *pgtable_alloc_one(struct mm_struct *mm, unsigned long address,
 	 */
 	for (i = 1; i < order; ++i) {
 		init_page_count(p+i);
+		__SetPageTable(p+i);
 		inc_zone_page_state(p+i, NR_PAGETABLE);
 	}
 
@@ -226,6 +227,7 @@ void pgtable_free(struct mm_struct *mm, struct page *p, int order)
 
 	for (i = 1; i < order; ++i) {
 		__free_page(p+i);
+		__ClearPageTable(p+i);
 		dec_zone_page_state(p+i, NR_PAGETABLE);
 	}
 }
@@ -240,6 +242,7 @@ void __pgtable_free_tlb(struct mmu_gather *tlb, struct page *pte,
 
 	for (i = 1; i < order; ++i) {
 		tlb_remove_page(tlb, pte + i);
+		__ClearPageTable(pte + i);
 		dec_zone_page_state(pte + i, NR_PAGETABLE);
 	}
 }
diff --git a/fs/proc/page.c b/fs/proc/page.c
index c9757af919a3..80275e7a963b 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -156,6 +156,8 @@ u64 stable_page_flags(struct page *page)
 		u |= 1 << KPF_BALLOON;
 	if (PageVmalloc(page))
 		u |= 1 << KPF_VMALLOC;
+	if (PageTable(page))
+		u |= 1 << KPF_PGTABLE;
 
 	if (page_is_idle(page))
 		u |= 1 << KPF_IDLE;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index ad06d42adb1a..7a15042d6828 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1829,6 +1829,7 @@ static inline bool pgtable_page_ctor(struct page *page)
 {
 	if (!ptlock_init(page))
 		return false;
+	__SetPageTable(page);
 	inc_zone_page_state(page, NR_PAGETABLE);
 	return true;
 }
@@ -1836,6 +1837,7 @@ static inline bool pgtable_page_ctor(struct page *page)
 static inline void pgtable_page_dtor(struct page *page)
 {
 	pte_lock_deinit(page);
+	__ClearPageTable(page);
 	dec_zone_page_state(page, NR_PAGETABLE);
 }
 
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 8142ab716e90..ac6bab90849c 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -644,6 +644,7 @@ PAGEFLAG_FALSE(DoubleMap)
 #define PG_balloon	0x00000100
 #define PG_kmemcg	0x00000200
 #define PG_vmalloc	0x00000400
+#define PG_table	0x00000800
 
 #define PageType(page, flag)						\
 	((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE)
@@ -687,6 +688,11 @@ PAGE_TYPE_OPS(Kmemcg, kmemcg)
  */
 PAGE_TYPE_OPS(Vmalloc, vmalloc)
 
+/*
+ * Marks pages in use as page tables.
+ */
+PAGE_TYPE_OPS(Table, table)
+
 extern bool is_free_buddy_page(struct page *page);
 
 __PAGEFLAG(Isolated, isolated, PF_ANY);
diff --git a/include/uapi/linux/kernel-page-flags.h b/include/uapi/linux/kernel-page-flags.h
index 5f1735ff05b3..3c51d8bf8b7b 100644
--- a/include/uapi/linux/kernel-page-flags.h
+++ b/include/uapi/linux/kernel-page-flags.h
@@ -36,5 +36,6 @@
 #define KPF_ZERO_PAGE		24
 #define KPF_IDLE		25
 #define KPF_VMALLOC		26
+#define KPF_PGTABLE		27
 
 #endif /* _UAPILINUX_KERNEL_PAGE_FLAGS_H */
diff --git a/tools/vm/page-types.c b/tools/vm/page-types.c
index 116f59eff5e2..bbb992694f05 100644
--- a/tools/vm/page-types.c
+++ b/tools/vm/page-types.c
@@ -132,6 +132,7 @@ static const char * const page_flag_names[] = {
 	[KPF_THP]		= "t:thp",
 	[KPF_BALLOON]		= "o:balloon",
 	[KPF_VMALLOC]		= "V:vmalloc",
+	[KPF_PGTABLE]		= "g:pgtable",
 	[KPF_ZERO_PAGE]		= "z:zero_page",
 	[KPF_IDLE]              = "i:idle_page",
 
-- 
2.16.1

Re: [PATCH v4 2/4] mm: Split page_type out from _map_count

[Kirill A. Shutemov]

On Thu, Mar 01, 2018 at 01:15:21PM -0800, Matthew Wilcox wrote:
> From: Matthew Wilcox <mawilcox@microsoft.com>
> 
> We're already using a union of many fields here, so stop abusing the
> _map_count and make page_type its own field.  That implies renaming some

s/_map_count/_mapcount/

and in subject.

> of the machinery that creates PageBuddy, PageBalloon and PageKmemcg;
> bring back the PG_buddy, PG_balloon and PG_kmemcg names.
> 
> As suggested by Kirill, make page_type a bitmask.  Because it starts out
> life as -1 (thanks to sharing the storage with _map_count), setting a
> page flag means clearing the appropriate bit.  This gives us space for
> probably twenty or so extra bits (depending how paranoid we want to be
> about _mapcount underflow).
> 
> Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
 Kirill A. Shutemov

Re: [PATCH v4 3/4] mm: Mark pages allocated through vmalloc

[Kirill A. Shutemov]

On Thu, Mar 01, 2018 at 01:15:22PM -0800, Matthew Wilcox wrote:
> From: Matthew Wilcox <mawilcox@microsoft.com>
> 
> Use a bit in page_type to mark pages which have been allocated through
> vmalloc.  This can be helpful when debugging crashdumps or analysing
> memory fragmentation.  Add a KPF flag to report these pages to userspace
> and update page-types.c to interpret that flag.
> 
> Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
 Kirill A. Shutemov

Re: [PATCH v4 4/4] mm: Mark pages in use for page tables

[Kirill A. Shutemov]

On Thu, Mar 01, 2018 at 01:15:23PM -0800, Matthew Wilcox wrote:
> From: Matthew Wilcox <mawilcox@microsoft.com>
> 
> Define a new PageTable bit in the page_type and use it to mark pages in
> use as page tables.  This can be helpful when debugging crashdumps or
> analysing memory fragmentation.  Add a KPF flag to report these pages
> to userspace and update page-types.c to interpret that flag.

I guess it's worth noting in the commit message that PGD and P4D page
tables are not acoounted to NR_PAGETABLE and not marked with PageTable().
> 
> Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
 Kirill A. Shutemov