linux/Documentation/mm/page_owner.rst
Linus Torvalds 3822a7c409 - Daniel Verkamp has contributed a memfd series ("mm/memfd: add
F_SEAL_EXEC") which permits the setting of the memfd execute bit at
   memfd creation time, with the option of sealing the state of the X bit.
 
 - Peter Xu adds a patch series ("mm/hugetlb: Make huge_pte_offset()
   thread-safe for pmd unshare") which addresses a rare race condition
   related to PMD unsharing.
 
 - Several folioification patch serieses from Matthew Wilcox, Vishal
   Moola, Sidhartha Kumar and Lorenzo Stoakes
 
 - Johannes Weiner has a series ("mm: push down lock_page_memcg()") which
   does perform some memcg maintenance and cleanup work.
 
 - SeongJae Park has added DAMOS filtering to DAMON, with the series
   "mm/damon/core: implement damos filter".  These filters provide users
   with finer-grained control over DAMOS's actions.  SeongJae has also done
   some DAMON cleanup work.
 
 - Kairui Song adds a series ("Clean up and fixes for swap").
 
 - Vernon Yang contributed the series "Clean up and refinement for maple
   tree".
 
 - Yu Zhao has contributed the "mm: multi-gen LRU: memcg LRU" series.  It
   adds to MGLRU an LRU of memcgs, to improve the scalability of global
   reclaim.
 
 - David Hildenbrand has added some userfaultfd cleanup work in the
   series "mm: uffd-wp + change_protection() cleanups".
 
 - Christoph Hellwig has removed the generic_writepages() library
   function in the series "remove generic_writepages".
 
 - Baolin Wang has performed some maintenance on the compaction code in
   his series "Some small improvements for compaction".
 
 - Sidhartha Kumar is doing some maintenance work on struct page in his
   series "Get rid of tail page fields".
 
 - David Hildenbrand contributed some cleanup, bugfixing and
   generalization of pte management and of pte debugging in his series "mm:
   support __HAVE_ARCH_PTE_SWP_EXCLUSIVE on all architectures with swap
   PTEs".
 
 - Mel Gorman and Neil Brown have removed the __GFP_ATOMIC allocation
   flag in the series "Discard __GFP_ATOMIC".
 
 - Sergey Senozhatsky has improved zsmalloc's memory utilization with his
   series "zsmalloc: make zspage chain size configurable".
 
 - Joey Gouly has added prctl() support for prohibiting the creation of
   writeable+executable mappings.  The previous BPF-based approach had
   shortcomings.  See "mm: In-kernel support for memory-deny-write-execute
   (MDWE)".
 
 - Waiman Long did some kmemleak cleanup and bugfixing in the series
   "mm/kmemleak: Simplify kmemleak_cond_resched() & fix UAF".
 
 - T.J.  Alumbaugh has contributed some MGLRU cleanup work in his series
   "mm: multi-gen LRU: improve".
 
 - Jiaqi Yan has provided some enhancements to our memory error
   statistics reporting, mainly by presenting the statistics on a per-node
   basis.  See the series "Introduce per NUMA node memory error
   statistics".
 
 - Mel Gorman has a second and hopefully final shot at fixing a CPU-hog
   regression in compaction via his series "Fix excessive CPU usage during
   compaction".
 
 - Christoph Hellwig does some vmalloc maintenance work in the series
   "cleanup vfree and vunmap".
 
 - Christoph Hellwig has removed block_device_operations.rw_page() in ths
   series "remove ->rw_page".
 
 - We get some maple_tree improvements and cleanups in Liam Howlett's
   series "VMA tree type safety and remove __vma_adjust()".
 
 - Suren Baghdasaryan has done some work on the maintainability of our
   vm_flags handling in the series "introduce vm_flags modifier functions".
 
 - Some pagemap cleanup and generalization work in Mike Rapoport's series
   "mm, arch: add generic implementation of pfn_valid() for FLATMEM" and
   "fixups for generic implementation of pfn_valid()"
 
 - Baoquan He has done some work to make /proc/vmallocinfo and
   /proc/kcore better represent the real state of things in his series
   "mm/vmalloc.c: allow vread() to read out vm_map_ram areas".
 
 - Jason Gunthorpe rationalized the GUP system's interface to the rest of
   the kernel in the series "Simplify the external interface for GUP".
 
 - SeongJae Park wishes to migrate people from DAMON's debugfs interface
   over to its sysfs interface.  To support this, we'll temporarily be
   printing warnings when people use the debugfs interface.  See the series
   "mm/damon: deprecate DAMON debugfs interface".
 
 - Andrey Konovalov provided the accurately named "lib/stackdepot: fixes
   and clean-ups" series.
 
 - Huang Ying has provided a dramatic reduction in migration's TLB flush
   IPI rates with the series "migrate_pages(): batch TLB flushing".
 
 - Arnd Bergmann has some objtool fixups in "objtool warning fixes".
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Merge tag 'mm-stable-2023-02-20-13-37' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Pull MM updates from Andrew Morton:

 - Daniel Verkamp has contributed a memfd series ("mm/memfd: add
   F_SEAL_EXEC") which permits the setting of the memfd execute bit at
   memfd creation time, with the option of sealing the state of the X
   bit.

 - Peter Xu adds a patch series ("mm/hugetlb: Make huge_pte_offset()
   thread-safe for pmd unshare") which addresses a rare race condition
   related to PMD unsharing.

 - Several folioification patch serieses from Matthew Wilcox, Vishal
   Moola, Sidhartha Kumar and Lorenzo Stoakes

 - Johannes Weiner has a series ("mm: push down lock_page_memcg()")
   which does perform some memcg maintenance and cleanup work.

 - SeongJae Park has added DAMOS filtering to DAMON, with the series
   "mm/damon/core: implement damos filter".

   These filters provide users with finer-grained control over DAMOS's
   actions. SeongJae has also done some DAMON cleanup work.

 - Kairui Song adds a series ("Clean up and fixes for swap").

 - Vernon Yang contributed the series "Clean up and refinement for maple
   tree".

 - Yu Zhao has contributed the "mm: multi-gen LRU: memcg LRU" series. It
   adds to MGLRU an LRU of memcgs, to improve the scalability of global
   reclaim.

 - David Hildenbrand has added some userfaultfd cleanup work in the
   series "mm: uffd-wp + change_protection() cleanups".

 - Christoph Hellwig has removed the generic_writepages() library
   function in the series "remove generic_writepages".

 - Baolin Wang has performed some maintenance on the compaction code in
   his series "Some small improvements for compaction".

 - Sidhartha Kumar is doing some maintenance work on struct page in his
   series "Get rid of tail page fields".

 - David Hildenbrand contributed some cleanup, bugfixing and
   generalization of pte management and of pte debugging in his series
   "mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE on all architectures with
   swap PTEs".

 - Mel Gorman and Neil Brown have removed the __GFP_ATOMIC allocation
   flag in the series "Discard __GFP_ATOMIC".

 - Sergey Senozhatsky has improved zsmalloc's memory utilization with
   his series "zsmalloc: make zspage chain size configurable".

 - Joey Gouly has added prctl() support for prohibiting the creation of
   writeable+executable mappings.

   The previous BPF-based approach had shortcomings. See "mm: In-kernel
   support for memory-deny-write-execute (MDWE)".

 - Waiman Long did some kmemleak cleanup and bugfixing in the series
   "mm/kmemleak: Simplify kmemleak_cond_resched() & fix UAF".

 - T.J. Alumbaugh has contributed some MGLRU cleanup work in his series
   "mm: multi-gen LRU: improve".

 - Jiaqi Yan has provided some enhancements to our memory error
   statistics reporting, mainly by presenting the statistics on a
   per-node basis. See the series "Introduce per NUMA node memory error
   statistics".

 - Mel Gorman has a second and hopefully final shot at fixing a CPU-hog
   regression in compaction via his series "Fix excessive CPU usage
   during compaction".

 - Christoph Hellwig does some vmalloc maintenance work in the series
   "cleanup vfree and vunmap".

 - Christoph Hellwig has removed block_device_operations.rw_page() in
   ths series "remove ->rw_page".

 - We get some maple_tree improvements and cleanups in Liam Howlett's
   series "VMA tree type safety and remove __vma_adjust()".

 - Suren Baghdasaryan has done some work on the maintainability of our
   vm_flags handling in the series "introduce vm_flags modifier
   functions".

 - Some pagemap cleanup and generalization work in Mike Rapoport's
   series "mm, arch: add generic implementation of pfn_valid() for
   FLATMEM" and "fixups for generic implementation of pfn_valid()"

 - Baoquan He has done some work to make /proc/vmallocinfo and
   /proc/kcore better represent the real state of things in his series
   "mm/vmalloc.c: allow vread() to read out vm_map_ram areas".

 - Jason Gunthorpe rationalized the GUP system's interface to the rest
   of the kernel in the series "Simplify the external interface for
   GUP".

 - SeongJae Park wishes to migrate people from DAMON's debugfs interface
   over to its sysfs interface. To support this, we'll temporarily be
   printing warnings when people use the debugfs interface. See the
   series "mm/damon: deprecate DAMON debugfs interface".

 - Andrey Konovalov provided the accurately named "lib/stackdepot: fixes
   and clean-ups" series.

 - Huang Ying has provided a dramatic reduction in migration's TLB flush
   IPI rates with the series "migrate_pages(): batch TLB flushing".

 - Arnd Bergmann has some objtool fixups in "objtool warning fixes".

* tag 'mm-stable-2023-02-20-13-37' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (505 commits)
  include/linux/migrate.h: remove unneeded externs
  mm/memory_hotplug: cleanup return value handing in do_migrate_range()
  mm/uffd: fix comment in handling pte markers
  mm: change to return bool for isolate_movable_page()
  mm: hugetlb: change to return bool for isolate_hugetlb()
  mm: change to return bool for isolate_lru_page()
  mm: change to return bool for folio_isolate_lru()
  objtool: add UACCESS exceptions for __tsan_volatile_read/write
  kmsan: disable ftrace in kmsan core code
  kasan: mark addr_has_metadata __always_inline
  mm: memcontrol: rename memcg_kmem_enabled()
  sh: initialize max_mapnr
  m68k/nommu: add missing definition of ARCH_PFN_OFFSET
  mm: percpu: fix incorrect size in pcpu_obj_full_size()
  maple_tree: reduce stack usage with gcc-9 and earlier
  mm: page_alloc: call panic() when memoryless node allocation fails
  mm: multi-gen LRU: avoid futile retries
  migrate_pages: move THP/hugetlb migration support check to simplify code
  migrate_pages: batch flushing TLB
  migrate_pages: share more code between _unmap and _move
  ...
2023-02-23 17:09:35 -08:00

188 lines
7.1 KiB
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==================================================
page owner: Tracking about who allocated each page
==================================================
Introduction
============
page owner is for the tracking about who allocated each page.
It can be used to debug memory leak or to find a memory hogger.
When allocation happens, information about allocation such as call stack
and order of pages is stored into certain storage for each page.
When we need to know about status of all pages, we can get and analyze
this information.
Although we already have tracepoint for tracing page allocation/free,
using it for analyzing who allocate each page is rather complex. We need
to enlarge the trace buffer for preventing overlapping until userspace
program launched. And, launched program continually dump out the trace
buffer for later analysis and it would change system behaviour with more
possibility rather than just keeping it in memory, so bad for debugging.
page owner can also be used for various purposes. For example, accurate
fragmentation statistics can be obtained through gfp flag information of
each page. It is already implemented and activated if page owner is
enabled. Other usages are more than welcome.
page owner is disabled by default. So, if you'd like to use it, you need
to add "page_owner=on" to your boot cmdline. If the kernel is built
with page owner and page owner is disabled in runtime due to not enabling
boot option, runtime overhead is marginal. If disabled in runtime, it
doesn't require memory to store owner information, so there is no runtime
memory overhead. And, page owner inserts just two unlikely branches into
the page allocator hotpath and if not enabled, then allocation is done
like as the kernel without page owner. These two unlikely branches should
not affect to allocation performance, especially if the static keys jump
label patching functionality is available. Following is the kernel's code
size change due to this facility.
Although enabling page owner increases kernel size by several kilobytes,
most of this code is outside page allocator and its hot path. Building
the kernel with page owner and turning it on if needed would be great
option to debug kernel memory problem.
There is one notice that is caused by implementation detail. page owner
stores information into the memory from struct page extension. This memory
is initialized some time later than that page allocator starts in sparse
memory system, so, until initialization, many pages can be allocated and
they would have no owner information. To fix it up, these early allocated
pages are investigated and marked as allocated in initialization phase.
Although it doesn't mean that they have the right owner information,
at least, we can tell whether the page is allocated or not,
more accurately. On 2GB memory x86-64 VM box, 13343 early allocated pages
are caught and marked, although they are mostly allocated from struct
page extension feature. Anyway, after that, no page is left in
un-tracking state.
Usage
=====
1) Build user-space helper::
cd tools/mm
make page_owner_sort
2) Enable page owner: add "page_owner=on" to boot cmdline.
3) Do the job that you want to debug.
4) Analyze information from page owner::
cat /sys/kernel/debug/page_owner > page_owner_full.txt
./page_owner_sort page_owner_full.txt sorted_page_owner.txt
The general output of ``page_owner_full.txt`` is as follows::
Page allocated via order XXX, ...
PFN XXX ...
// Detailed stack
Page allocated via order XXX, ...
PFN XXX ...
// Detailed stack
By default, it will do full pfn dump, to start with a given pfn,
page_owner supports fseek.
FILE *fp = fopen("/sys/kernel/debug/page_owner", "r");
fseek(fp, pfn_start, SEEK_SET);
The ``page_owner_sort`` tool ignores ``PFN`` rows, puts the remaining rows
in buf, uses regexp to extract the page order value, counts the times
and pages of buf, and finally sorts them according to the parameter(s).
See the result about who allocated each page
in the ``sorted_page_owner.txt``. General output::
XXX times, XXX pages:
Page allocated via order XXX, ...
// Detailed stack
By default, ``page_owner_sort`` is sorted according to the times of buf.
If you want to sort by the page nums of buf, use the ``-m`` parameter.
The detailed parameters are:
fundamental function::
Sort:
-a Sort by memory allocation time.
-m Sort by total memory.
-p Sort by pid.
-P Sort by tgid.
-n Sort by task command name.
-r Sort by memory release time.
-s Sort by stack trace.
-t Sort by times (default).
--sort <order> Specify sorting order. Sorting syntax is [+|-]key[,[+|-]key[,...]].
Choose a key from the **STANDARD FORMAT SPECIFIERS** section. The "+" is
optional since default direction is increasing numerical or lexicographic
order. Mixed use of abbreviated and complete-form of keys is allowed.
Examples:
./page_owner_sort <input> <output> --sort=n,+pid,-tgid
./page_owner_sort <input> <output> --sort=at
additional function::
Cull:
--cull <rules>
Specify culling rules.Culling syntax is key[,key[,...]].Choose a
multi-letter key from the **STANDARD FORMAT SPECIFIERS** section.
<rules> is a single argument in the form of a comma-separated list,
which offers a way to specify individual culling rules. The recognized
keywords are described in the **STANDARD FORMAT SPECIFIERS** section below.
<rules> can be specified by the sequence of keys k1,k2, ..., as described in
the STANDARD SORT KEYS section below. Mixed use of abbreviated and
complete-form of keys is allowed.
Examples:
./page_owner_sort <input> <output> --cull=stacktrace
./page_owner_sort <input> <output> --cull=st,pid,name
./page_owner_sort <input> <output> --cull=n,f
Filter:
-f Filter out the information of blocks whose memory has been released.
Select:
--pid <pidlist> Select by pid. This selects the blocks whose process ID
numbers appear in <pidlist>.
--tgid <tgidlist> Select by tgid. This selects the blocks whose thread
group ID numbers appear in <tgidlist>.
--name <cmdlist> Select by task command name. This selects the blocks whose
task command name appear in <cmdlist>.
<pidlist>, <tgidlist>, <cmdlist> are single arguments in the form of a comma-separated list,
which offers a way to specify individual selecting rules.
Examples:
./page_owner_sort <input> <output> --pid=1
./page_owner_sort <input> <output> --tgid=1,2,3
./page_owner_sort <input> <output> --name name1,name2
STANDARD FORMAT SPECIFIERS
==========================
::
For --sort option:
KEY LONG DESCRIPTION
p pid process ID
tg tgid thread group ID
n name task command name
st stacktrace stack trace of the page allocation
T txt full text of block
ft free_ts timestamp of the page when it was released
at alloc_ts timestamp of the page when it was allocated
ator allocator memory allocator for pages
For --cull option:
KEY LONG DESCRIPTION
p pid process ID
tg tgid thread group ID
n name task command name
f free whether the page has been released or not
st stacktrace stack trace of the page allocation
ator allocator memory allocator for pages