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Commit 17e89501 authored by Wu Fengguang's avatar Wu Fengguang Committed by Linus Torvalds
Browse files

pagemap: document 9 more exported page flags 



Also add short descriptions for all of the 20 exported page flags.

Signed-off-by: default avatarWu Fengguang <fengguang.wu@intel.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c9ba78e2

Documentation/vm/pagemap.txt

+62 −0
Original line number Diff line number Diff line
@@ -49,6 +49,68 @@ There are three components to pagemap: 
     8. WRITEBACK

     9. RECLAIM

    10. BUDDY

    11. MMAP

    12. ANON

    13. SWAPCACHE

    14. SWAPBACKED

    15. COMPOUND_HEAD

    16. COMPOUND_TAIL

    16. HUGE

    18. UNEVICTABLE

    20. NOPAGE



Short descriptions to the page flags:



 0. LOCKED

    page is being locked for exclusive access, eg. by undergoing read/write IO



 7. SLAB

    page is managed by the SLAB/SLOB/SLUB/SLQB kernel memory allocator

    When compound page is used, SLUB/SLQB will only set this flag on the head

    page; SLOB will not flag it at all.



10. BUDDY

    a free memory block managed by the buddy system allocator

    The buddy system organizes free memory in blocks of various orders.

    An order N block has 2^N physically contiguous pages, with the BUDDY flag

    set for and _only_ for the first page.



15. COMPOUND_HEAD

16. COMPOUND_TAIL

    A compound page with order N consists of 2^N physically contiguous pages.

    A compound page with order 2 takes the form of "HTTT", where H donates its

    head page and T donates its tail page(s).  The major consumers of compound

    pages are hugeTLB pages (Documentation/vm/hugetlbpage.txt), the SLUB etc.

    memory allocators and various device drivers. However in this interface,

    only huge/giga pages are made visible to end users.

17. HUGE

    this is an integral part of a HugeTLB page



20. NOPAGE

    no page frame exists at the requested address



    [IO related page flags]

 1. ERROR     IO error occurred

 3. UPTODATE  page has up-to-date data

              ie. for file backed page: (in-memory data revision >= on-disk one)

 4. DIRTY     page has been written to, hence contains new data

              ie. for file backed page: (in-memory data revision >  on-disk one)

 8. WRITEBACK page is being synced to disk



    [LRU related page flags]

 5. LRU         page is in one of the LRU lists

 6. ACTIVE      page is in the active LRU list

18. UNEVICTABLE page is in the unevictable (non-)LRU list

                It is somehow pinned and not a candidate for LRU page reclaims,

		eg. ramfs pages, shmctl(SHM_LOCK) and mlock() memory segments

 2. REFERENCED  page has been referenced since last LRU list enqueue/requeue

 9. RECLAIM     page will be reclaimed soon after its pageout IO completed

11. MMAP        a memory mapped page

12. ANON        a memory mapped page that is not part of a file

13. SWAPCACHE   page is mapped to swap space, ie. has an associated swap entry

14. SWAPBACKED  page is backed by swap/RAM



The page-types tool in this directory can be used to query the above flags.



Using pagemap to do something useful: