diff options
Diffstat (limited to 'Documentation/vm/pagemap.txt')
| -rw-r--r-- | Documentation/vm/pagemap.txt | 68 |
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: |