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-rw-r--r--Documentation/vm/pagemap.txt68
1 files changed, 65 insertions, 3 deletions
diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt
index ce72c0fe6177..600a304a828c 100644
--- a/Documentation/vm/pagemap.txt
+++ b/Documentation/vm/pagemap.txt
@@ -12,9 +12,9 @@ There are three components to pagemap:
value for each virtual page, containing the following data (from
fs/proc/task_mmu.c, above pagemap_read):
- * Bits 0-55 page frame number (PFN) if present
+ * Bits 0-54 page frame number (PFN) if present
* Bits 0-4 swap type if swapped
- * Bits 5-55 swap offset if swapped
+ * Bits 5-54 swap offset if swapped
* Bits 55-60 page shift (page size = 1<<page shift)
* Bit 61 reserved for future use
* Bit 62 page swapped
@@ -36,7 +36,7 @@ There are three components to pagemap:
* /proc/kpageflags. This file contains a 64-bit set of flags for each
page, indexed by PFN.
- The flags are (from fs/proc/proc_misc, above kpageflags_read):
+ The flags are (from fs/proc/page.c, above kpageflags_read):
0. LOCKED
1. ERROR
@@ -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: