Commit 77bb499b authored by Konstantin Khlebnikov's avatar Konstantin Khlebnikov Committed by Linus Torvalds
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pagemap: add mmap-exclusive bit for marking pages mapped only here 

This patch sets bit 56 in pagemap if this page is mapped only once.  It
allows to detect exclusively used pages without exposing PFN:

present file exclusive state
0       0    0         non-present
1       1    0         file page mapped somewhere else
1       1    1         file page mapped only here
1       0    0         anon non-CoWed page (shared with parent/child)
1       0    1         anon CoWed page (or never forked)

CoWed pages in (MAP_FILE | MAP_PRIVATE) areas are anon in this context.

MMap-exclusive bit doesn't reflect potential page-sharing via swapcache:
page could be mapped once but has several swap-ptes which point to it.
Application could detect that by swap bit in pagemap entry and touch that
pte via /proc/pid/mem to get real information.

See http://lkml.kernel.org/r/CAEVpBa+_RyACkhODZrRvQLs80iy0sqpdrd0AaP_-tgnX3Y9yNQ@mail.gmail.com



Requested by Mark Williamson.

[akpm@linux-foundation.org: fix spello]
Signed-off-by: default avatarKonstantin Khlebnikov <khlebnikov@yandex-team.ru>
Reviewed-by: default avatarMark Williamson <mwilliamson@undo-software.com>
Tested-by: default avatarMark Williamson <mwilliamson@undo-software.com>
Reviewed-by: default avatarNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1c90308e

Documentation/vm/pagemap.txt

+2 −1
Original line number Diff line number Diff line
@@ -16,7 +16,8 @@ There are three components to pagemap: 
    * Bits 0-4   swap type if swapped

    * Bits 5-54  swap offset if swapped

    * Bit  55    pte is soft-dirty (see Documentation/vm/soft-dirty.txt)

    * Bits 56-60 zero

    * Bit  56    page exclusively mapped

    * Bits 57-60 zero

    * Bit  61    page is file-page or shared-anon

    * Bit  62    page swapped

    * Bit  63    page present

fs/proc/task_mmu.c

+13 −1
Original line number Diff line number Diff line
@@ -949,6 +949,7 @@ struct pagemapread { 
#define PM_PFRAME_BITS		55

#define PM_PFRAME_MASK		GENMASK_ULL(PM_PFRAME_BITS - 1, 0)

#define PM_SOFT_DIRTY		BIT_ULL(55)

#define PM_MMAP_EXCLUSIVE	BIT_ULL(56)

#define PM_FILE			BIT_ULL(61)

#define PM_SWAP			BIT_ULL(62)

#define PM_PRESENT		BIT_ULL(63)
@@ -1036,6 +1037,8 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm, 


	if (page && !PageAnon(page))

		flags |= PM_FILE;

	if (page && page_mapcount(page) == 1)

		flags |= PM_MMAP_EXCLUSIVE;

	if (vma->vm_flags & VM_SOFTDIRTY)

		flags |= PM_SOFT_DIRTY;
@@ -1066,6 +1069,11 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end, 
		 * This if-check is just to prepare for future implementation.

		 */

		if (pmd_present(pmd)) {

			struct page *page = pmd_page(pmd);



			if (page_mapcount(page) == 1)

				flags |= PM_MMAP_EXCLUSIVE;



			flags |= PM_PRESENT;

			if (pm->show_pfn)

				frame = pmd_pfn(pmd) +
@@ -1131,6 +1139,9 @@ static int pagemap_hugetlb_range(pte_t *ptep, unsigned long hmask, 
		if (!PageAnon(page))

			flags |= PM_FILE;



		if (page_mapcount(page) == 1)

			flags |= PM_MMAP_EXCLUSIVE;



		flags |= PM_PRESENT;

		if (pm->show_pfn)

			frame = pte_pfn(pte) +
@@ -1163,7 +1174,8 @@ static int pagemap_hugetlb_range(pte_t *ptep, unsigned long hmask, 
 * Bits 0-4   swap type if swapped

 * Bits 5-54  swap offset if swapped

 * Bit  55    pte is soft-dirty (see Documentation/vm/soft-dirty.txt)

 * Bits 56-60 zero

 * Bit  56    page exclusively mapped

 * Bits 57-60 zero

 * Bit  61    page is file-page or shared-anon

 * Bit  62    page swapped

 * Bit  63    page present

tools/vm/page-types.c

+10 −0
Original line number Diff line number Diff line
@@ -62,6 +62,7 @@ 
#define PM_PFRAME_MASK		((1LL << PM_PFRAME_BITS) - 1)

#define PM_PFRAME(x)		((x) & PM_PFRAME_MASK)

#define PM_SOFT_DIRTY		(1ULL << 55)

#define PM_MMAP_EXCLUSIVE	(1ULL << 56)

#define PM_FILE			(1ULL << 61)

#define PM_SWAP			(1ULL << 62)

#define PM_PRESENT		(1ULL << 63)
@@ -91,6 +92,8 @@ 
#define KPF_SLOB_FREE		49

#define KPF_SLUB_FROZEN		50

#define KPF_SLUB_DEBUG		51

#define KPF_FILE		62

#define KPF_MMAP_EXCLUSIVE	63



#define KPF_ALL_BITS		((uint64_t)~0ULL)

#define KPF_HACKERS_BITS	(0xffffULL << 32)
@@ -140,6 +143,9 @@ static const char * const page_flag_names[] = { 
	[KPF_SLOB_FREE]		= "P:slob_free",

	[KPF_SLUB_FROZEN]	= "A:slub_frozen",

	[KPF_SLUB_DEBUG]	= "E:slub_debug",



	[KPF_FILE]		= "F:file",

	[KPF_MMAP_EXCLUSIVE]	= "1:mmap_exclusive",

};
@@ -443,6 +449,10 @@ static uint64_t expand_overloaded_flags(uint64_t flags, uint64_t pme) 


	if (pme & PM_SOFT_DIRTY)

		flags |= BIT(SOFTDIRTY);

	if (pme & PM_FILE)

		flags |= BIT(FILE);

	if (pme & PM_MMAP_EXCLUSIVE)

		flags |= BIT(MMAP_EXCLUSIVE);



	return flags;

}

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