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: