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pagemap: add mmap-exclusive bit for marking pages mapped only here

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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: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Reviewed-by: Mark Williamson <mwilliamson@undo-software.com>
Tested-by:  Mark Williamson <mwilliamson@undo-software.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Konstantin Khlebnikov 2015-09-08 15:00:10 -07:00 committed by Linus Torvalds
parent 1c90308e7a
commit 77bb499bb6
3 changed files with 25 additions and 2 deletions
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3
Documentation/vm/pagemap.txt
View file

@ -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

14
fs/proc/task_mmu.c
View file

@ -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

10
tools/vm/page-types.c
View file

@ -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;
}