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Diffstat (limited to 'Documentation/vm/pagemap.txt')
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diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt deleted file mode 100644 index 7587493..0000000 --- a/Documentation/vm/pagemap.txt +++ /dev/null @@ -1,151 +0,0 @@ -pagemap, from the userspace perspective ---------------------------------------- - -pagemap is a new (as of 2.6.25) set of interfaces in the kernel that allow -userspace programs to examine the page tables and related information by -reading files in /proc. - -There are three components to pagemap: - - * /proc/pid/pagemap. This file lets a userspace process find out which - physical frame each virtual page is mapped to. It contains one 64-bit - value for each virtual page, containing the following data (from - fs/proc/task_mmu.c, above pagemap_read): - - * Bits 0-54 page frame number (PFN) if present - * Bits 0-4 swap type if swapped - * Bits 5-54 swap offset if swapped - * Bits 55-60 page shift (page size = 1<<page shift) - * Bit 61 page is file-page or shared-anon - * Bit 62 page swapped - * Bit 63 page present - - If the page is not present but in swap, then the PFN contains an - encoding of the swap file number and the page's offset into the - swap. Unmapped pages return a null PFN. This allows determining - precisely which pages are mapped (or in swap) and comparing mapped - pages between processes. - - Efficient users of this interface will use /proc/pid/maps to - determine which areas of memory are actually mapped and llseek to - skip over unmapped regions. - - * /proc/kpagecount. This file contains a 64-bit count of the number of - times each page is mapped, indexed by PFN. - - * /proc/kpageflags. This file contains a 64-bit set of flags for each - page, indexed by PFN. - - The flags are (from fs/proc/page.c, above kpageflags_read): - - 0. LOCKED - 1. ERROR - 2. REFERENCED - 3. UPTODATE - 4. DIRTY - 5. LRU - 6. ACTIVE - 7. SLAB - 8. WRITEBACK - 9. RECLAIM - 10. BUDDY - 11. MMAP - 12. ANON - 13. SWAPCACHE - 14. SWAPBACKED - 15. COMPOUND_HEAD - 16. COMPOUND_TAIL - 16. HUGE - 18. UNEVICTABLE - 19. HWPOISON - 20. NOPAGE - 21. KSM - 22. THP - -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 - -19. HWPOISON - hardware detected memory corruption on this page: don't touch the data! - -20. NOPAGE - no page frame exists at the requested address - -21. KSM - identical memory pages dynamically shared between one or more processes - -22. THP - contiguous pages which construct transparent hugepages - - [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: - -The general procedure for using pagemap to find out about a process' memory -usage goes like this: - - 1. Read /proc/pid/maps to determine which parts of the memory space are - mapped to what. - 2. Select the maps you are interested in -- all of them, or a particular - library, or the stack or the heap, etc. - 3. Open /proc/pid/pagemap and seek to the pages you would like to examine. - 4. Read a u64 for each page from pagemap. - 5. Open /proc/kpagecount and/or /proc/kpageflags. For each PFN you just - read, seek to that entry in the file, and read the data you want. - -For example, to find the "unique set size" (USS), which is the amount of -memory that a process is using that is not shared with any other process, -you can go through every map in the process, find the PFNs, look those up -in kpagecount, and tally up the number of pages that are only referenced -once. - -Other notes: - -Reading from any of the files will return -EINVAL if you are not starting -the read on an 8-byte boundary (e.g., if you seeked an odd number of bytes -into the file), or if the size of the read is not a multiple of 8 bytes. |