diff options
author | Wu Fengguang <fengguang.wu@intel.com> | 2009-06-16 18:32:26 -0400 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-06-16 22:47:38 -0400 |
commit | 17e895012f7fe9dc63144990da98c41bbc22d68f (patch) | |
tree | 430c333e2d23bf2fbf057ec9a5b3685eba217d99 | |
parent | c9ba78e226057a1c2f19671383c496df187c02b5 (diff) |
pagemap: document 9 more exported page flags
Also add short descriptions for all of the 20 exported page flags.
Signed-off-by: Wu 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r-- | Documentation/vm/pagemap.txt | 62 |
1 files changed, 62 insertions, 0 deletions
diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt index 1f1e69f72fcd..600a304a828c 100644 --- a/Documentation/vm/pagemap.txt +++ b/Documentation/vm/pagemap.txt | |||
@@ -49,6 +49,68 @@ There are three components to pagemap: | |||
49 | 8. WRITEBACK | 49 | 8. WRITEBACK |
50 | 9. RECLAIM | 50 | 9. RECLAIM |
51 | 10. BUDDY | 51 | 10. BUDDY |
52 | 11. MMAP | ||
53 | 12. ANON | ||
54 | 13. SWAPCACHE | ||
55 | 14. SWAPBACKED | ||
56 | 15. COMPOUND_HEAD | ||
57 | 16. COMPOUND_TAIL | ||
58 | 16. HUGE | ||
59 | 18. UNEVICTABLE | ||
60 | 20. NOPAGE | ||
61 | |||
62 | Short descriptions to the page flags: | ||
63 | |||
64 | 0. LOCKED | ||
65 | page is being locked for exclusive access, eg. by undergoing read/write IO | ||
66 | |||
67 | 7. SLAB | ||
68 | page is managed by the SLAB/SLOB/SLUB/SLQB kernel memory allocator | ||
69 | When compound page is used, SLUB/SLQB will only set this flag on the head | ||
70 | page; SLOB will not flag it at all. | ||
71 | |||
72 | 10. BUDDY | ||
73 | a free memory block managed by the buddy system allocator | ||
74 | The buddy system organizes free memory in blocks of various orders. | ||
75 | An order N block has 2^N physically contiguous pages, with the BUDDY flag | ||
76 | set for and _only_ for the first page. | ||
77 | |||
78 | 15. COMPOUND_HEAD | ||
79 | 16. COMPOUND_TAIL | ||
80 | A compound page with order N consists of 2^N physically contiguous pages. | ||
81 | A compound page with order 2 takes the form of "HTTT", where H donates its | ||
82 | head page and T donates its tail page(s). The major consumers of compound | ||
83 | pages are hugeTLB pages (Documentation/vm/hugetlbpage.txt), the SLUB etc. | ||
84 | memory allocators and various device drivers. However in this interface, | ||
85 | only huge/giga pages are made visible to end users. | ||
86 | 17. HUGE | ||
87 | this is an integral part of a HugeTLB page | ||
88 | |||
89 | 20. NOPAGE | ||
90 | no page frame exists at the requested address | ||
91 | |||
92 | [IO related page flags] | ||
93 | 1. ERROR IO error occurred | ||
94 | 3. UPTODATE page has up-to-date data | ||
95 | ie. for file backed page: (in-memory data revision >= on-disk one) | ||
96 | 4. DIRTY page has been written to, hence contains new data | ||
97 | ie. for file backed page: (in-memory data revision > on-disk one) | ||
98 | 8. WRITEBACK page is being synced to disk | ||
99 | |||
100 | [LRU related page flags] | ||
101 | 5. LRU page is in one of the LRU lists | ||
102 | 6. ACTIVE page is in the active LRU list | ||
103 | 18. UNEVICTABLE page is in the unevictable (non-)LRU list | ||
104 | It is somehow pinned and not a candidate for LRU page reclaims, | ||
105 | eg. ramfs pages, shmctl(SHM_LOCK) and mlock() memory segments | ||
106 | 2. REFERENCED page has been referenced since last LRU list enqueue/requeue | ||
107 | 9. RECLAIM page will be reclaimed soon after its pageout IO completed | ||
108 | 11. MMAP a memory mapped page | ||
109 | 12. ANON a memory mapped page that is not part of a file | ||
110 | 13. SWAPCACHE page is mapped to swap space, ie. has an associated swap entry | ||
111 | 14. SWAPBACKED page is backed by swap/RAM | ||
112 | |||
113 | The page-types tool in this directory can be used to query the above flags. | ||
52 | 114 | ||
53 | Using pagemap to do something useful: | 115 | Using pagemap to do something useful: |
54 | 116 | ||