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docs/vm: pagemap.txt: convert to ReST format

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Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Mike Rapoport 2018-03-21 21:22:33 +02:00 committed by Jonathan Corbet
parent 137b45527e
commit 25c3bf8aaf
1 changed files with 85 additions and 71 deletions
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156
Documentation/vm/pagemap.txt
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@ -1,13 +1,16 @@
pagemap, from the userspace perspective .. _pagemap:
---------------------------------------
======================================
pagemap from the Userspace Perspective
======================================
pagemap is a new (as of 2.6.25) set of interfaces in the kernel that allow 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 userspace programs to examine the page tables and related information by
reading files in /proc. reading files in ``/proc``.
There are four components to pagemap: There are four components to pagemap:
* /proc/pid/pagemap. This file lets a userspace process find out which * ``/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 physical frame each virtual page is mapped to. It contains one 64-bit
value for each virtual page, containing the following data (from value for each virtual page, containing the following data (from
fs/proc/task_mmu.c, above pagemap_read): fs/proc/task_mmu.c, above pagemap_read):
@ -37,24 +40,24 @@ There are four components to pagemap:
determine which areas of memory are actually mapped and llseek to determine which areas of memory are actually mapped and llseek to
skip over unmapped regions. skip over unmapped regions.
* /proc/kpagecount. This file contains a 64-bit count of the number of * ``/proc/kpagecount``. This file contains a 64-bit count of the number of
times each page is mapped, indexed by PFN. times each page is mapped, indexed by PFN.
* /proc/kpageflags. This file contains a 64-bit set of flags for each * ``/proc/kpageflags``. This file contains a 64-bit set of flags for each
page, indexed by PFN. page, indexed by PFN.
The flags are (from fs/proc/page.c, above kpageflags_read): The flags are (from ``fs/proc/page.c``, above kpageflags_read):
0. LOCKED 0. LOCKED
1. ERROR 1. ERROR
2. REFERENCED 2. REFERENCED
3. UPTODATE 3. UPTODATE
4. DIRTY 4. DIRTY
5. LRU 5. LRU
6. ACTIVE 6. ACTIVE
7. SLAB 7. SLAB
8. WRITEBACK 8. WRITEBACK
9. RECLAIM 9. RECLAIM
10. BUDDY 10. BUDDY
11. MMAP 11. MMAP
12. ANON 12. ANON
@ -72,98 +75,108 @@ There are four components to pagemap:
24. ZERO_PAGE 24. ZERO_PAGE
25. IDLE 25. IDLE
* /proc/kpagecgroup. This file contains a 64-bit inode number of the * ``/proc/kpagecgroup``. This file contains a 64-bit inode number of the
memory cgroup each page is charged to, indexed by PFN. Only available when memory cgroup each page is charged to, indexed by PFN. Only available when
CONFIG_MEMCG is set. CONFIG_MEMCG is set.
Short descriptions to the page flags: Short descriptions to the page flags:
=====================================
0. LOCKED 0 - LOCKED
page is being locked for exclusive access, eg. by undergoing read/write IO page is being locked for exclusive access, eg. by undergoing read/write IO
7 - SLAB
7. SLAB page is managed by the SLAB/SLOB/SLUB/SLQB kernel memory allocator
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
When compound page is used, SLUB/SLQB will only set this flag on the head page; SLOB will not flag it at all.
page; SLOB will not flag it at all. 10 - BUDDY
10. BUDDY
a free memory block managed by the buddy system allocator a free memory block managed by the buddy system allocator
The buddy system organizes free memory in blocks of various orders. 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 An order N block has 2^N physically contiguous pages, with the BUDDY flag
set for and _only_ for the first page. set for and _only_ for the first page.
15 - COMPOUND_HEAD
15. COMPOUND_HEAD
16. COMPOUND_TAIL
A compound page with order N consists of 2^N physically contiguous pages. 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 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 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. pages are hugeTLB pages (Documentation/vm/hugetlbpage.txt), the SLUB etc.
memory allocators and various device drivers. However in this interface, memory allocators and various device drivers. However in this interface,
only huge/giga pages are made visible to end users. only huge/giga pages are made visible to end users.
17. HUGE 16 - COMPOUND_TAIL
A compound page tail (see description above).
17 - HUGE
this is an integral part of a HugeTLB page this is an integral part of a HugeTLB page
19 - HWPOISON
19. HWPOISON
hardware detected memory corruption on this page: don't touch the data! hardware detected memory corruption on this page: don't touch the data!
20 - NOPAGE
20. NOPAGE
no page frame exists at the requested address no page frame exists at the requested address
21 - KSM
21. KSM
identical memory pages dynamically shared between one or more processes identical memory pages dynamically shared between one or more processes
22 - THP
22. THP
contiguous pages which construct transparent hugepages contiguous pages which construct transparent hugepages
23 - BALLOON
23. BALLOON
balloon compaction page balloon compaction page
24 - ZERO_PAGE
24. ZERO_PAGE
zero page for pfn_zero or huge_zero page zero page for pfn_zero or huge_zero page
25 - IDLE
25. IDLE
page has not been accessed since it was marked idle (see page has not been accessed since it was marked idle (see
Documentation/vm/idle_page_tracking.txt). Note that this flag may be Documentation/vm/idle_page_tracking.txt). Note that this flag may be
stale in case the page was accessed via a PTE. To make sure the flag stale in case the page was accessed via a PTE. To make sure the flag
is up-to-date one has to read /sys/kernel/mm/page_idle/bitmap first. is up-to-date one has to read ``/sys/kernel/mm/page_idle/bitmap`` first.
[IO related page flags] 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] 1 - ERROR
5. LRU page is in one of the LRU lists IO error occurred
6. ACTIVE page is in the active LRU list 3 - UPTODATE
18. UNEVICTABLE page is in the unevictable (non-)LRU list page has up-to-date data
It is somehow pinned and not a candidate for LRU page reclaims, ie. for file backed page: (in-memory data revision >= on-disk one)
eg. ramfs pages, shmctl(SHM_LOCK) and mlock() memory segments 4 - DIRTY
2. REFERENCED page has been referenced since last LRU list enqueue/requeue page has been written to, hence contains new data
9. RECLAIM page will be reclaimed soon after its pageout IO completed ie. for file backed page: (in-memory data revision > on-disk one)
11. MMAP a memory mapped page 8 - WRITEBACK
12. ANON a memory mapped page that is not part of a file page is being synced to disk
13. SWAPCACHE page is mapped to swap space, ie. has an associated swap entry
14. SWAPBACKED page is backed by swap/RAM 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 the tools/vm directory can be used to query the The page-types tool in the tools/vm directory can be used to query the
above flags. above flags.
Using pagemap to do something useful: Using pagemap to do something useful
====================================
The general procedure for using pagemap to find out about a process' memory The general procedure for using pagemap to find out about a process' memory
usage goes like this: usage goes like this:
1. Read /proc/pid/maps to determine which parts of the memory space are 1. Read ``/proc/pid/maps`` to determine which parts of the memory space are
mapped to what. mapped to what.
2. Select the maps you are interested in -- all of them, or a particular 2. Select the maps you are interested in -- all of them, or a particular
library, or the stack or the heap, etc. library, or the stack or the heap, etc.
3. Open /proc/pid/pagemap and seek to the pages you would like to examine. 3. Open ``/proc/pid/pagemap`` and seek to the pages you would like to examine.
4. Read a u64 for each page from pagemap. 4. Read a u64 for each page from pagemap.
5. Open /proc/kpagecount and/or /proc/kpageflags. For each PFN you just 5. Open ``/proc/kpagecount`` and/or ``/proc/kpageflags``. For each PFN you
read, seek to that entry in the file, and read the data you want. 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 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, memory that a process is using that is not shared with any other process,
@ -171,7 +184,8 @@ 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 in kpagecount, and tally up the number of pages that are only referenced
once. once.
Other notes: Other notes
===========
Reading from any of the files will return -EINVAL if you are not starting 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 sought an odd number of bytes the read on an 8-byte boundary (e.g., if you sought an odd number of bytes