linux/Documentation/vm
Konstantin Khlebnikov 77bb499bb6 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>
2015-09-08 15:35:28 -07:00
..
.gitignore
00-INDEX Documentation/: update 00-INDEX files 2014-02-10 16:01:40 -08:00
active_mm.txt
balance
cleancache.txt cleancache: forbid overriding cleancache_ops 2015-04-14 16:49:03 -07:00
frontswap.txt doc: fix quite a few typos within Documentation 2012-11-19 14:28:24 +01:00
highmem.txt
hugetlbpage.txt mm, doc: cleanup and clarify munmap behavior for hugetlb memory 2015-04-15 16:35:19 -07:00
hwpoison.txt mm/memory-failure.c: support use of a dedicated thread to handle SIGBUS(BUS_MCEERR_AO) 2014-06-04 16:54:13 -07:00
ksm.txt ksm: add some comments 2013-02-23 17:50:23 -08:00
numa
numa_memory_policy.txt Documentation/vm/numa_memory_policy.txt: fix wrong document in numa_memory_policy.txt 2014-04-18 16:40:08 -07:00
overcommit-accounting mm: add overcommit_kbytes sysctl variable 2014-01-21 16:19:44 -08:00
page_migration
page_owner.txt Documentation: add new page_owner document 2014-12-13 12:42:48 -08:00
pagemap.txt pagemap: add mmap-exclusive bit for marking pages mapped only here 2015-09-08 15:35:28 -07:00
remap_file_pages.txt mm: replace remap_file_pages() syscall with emulation 2015-02-10 14:30:30 -08:00
slub.txt Documentations: Fix slabinfo.c directory in vm/slub.txt 2012-05-10 11:45:23 +03:00
soft-dirty.txt mm: track vma changes with VM_SOFTDIRTY bit 2013-09-11 15:57:56 -07:00
split_page_table_lock x86, mm: do not leak page->ptl for pmd page tables 2013-11-21 16:42:28 -08:00
transhuge.txt doc: add information about max_ptes_none 2015-03-20 07:41:55 -06:00
unevictable-lru.txt Documentation/vm/unevictable-lru.txt: clarify MAP_LOCKED behavior 2015-06-24 17:49:44 -07:00
userfaultfd.txt userfaultfd: change the read API to return a uffd_msg 2015-09-04 16:54:41 -07:00
zsmalloc.txt zsmalloc: zsmalloc documentation 2015-04-15 16:35:21 -07:00
zswap.txt zswap: runtime enable/disable 2015-06-25 17:00:37 -07:00