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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: 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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

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;
}