linux/Documentation/mm/slub.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".
 -----BEGIN PGP SIGNATURE-----
 
 iHUEABYIAB0WIQTTMBEPP41GrTpTJgfdBJ7gKXxAjgUCY/PoPQAKCRDdBJ7gKXxA
 jlvpAPsFECUBBl20qSue2zCYWnHC7Yk4q9ytTkPB/MMDrFEN9wD/SNKEm2UoK6/K
 DmxHkn0LAitGgJRS/W9w81yrgig9tAQ=
 =MlGs
 -----END PGP SIGNATURE-----

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

462 lines
17 KiB
ReStructuredText

==========================
Short users guide for SLUB
==========================
The basic philosophy of SLUB is very different from SLAB. SLAB
requires rebuilding the kernel to activate debug options for all
slab caches. SLUB always includes full debugging but it is off by default.
SLUB can enable debugging only for selected slabs in order to avoid
an impact on overall system performance which may make a bug more
difficult to find.
In order to switch debugging on one can add an option ``slub_debug``
to the kernel command line. That will enable full debugging for
all slabs.
Typically one would then use the ``slabinfo`` command to get statistical
data and perform operation on the slabs. By default ``slabinfo`` only lists
slabs that have data in them. See "slabinfo -h" for more options when
running the command. ``slabinfo`` can be compiled with
::
gcc -o slabinfo tools/mm/slabinfo.c
Some of the modes of operation of ``slabinfo`` require that slub debugging
be enabled on the command line. F.e. no tracking information will be
available without debugging on and validation can only partially
be performed if debugging was not switched on.
Some more sophisticated uses of slub_debug:
-------------------------------------------
Parameters may be given to ``slub_debug``. If none is specified then full
debugging is enabled. Format:
slub_debug=<Debug-Options>
Enable options for all slabs
slub_debug=<Debug-Options>,<slab name1>,<slab name2>,...
Enable options only for select slabs (no spaces
after a comma)
Multiple blocks of options for all slabs or selected slabs can be given, with
blocks of options delimited by ';'. The last of "all slabs" blocks is applied
to all slabs except those that match one of the "select slabs" block. Options
of the first "select slabs" blocks that matches the slab's name are applied.
Possible debug options are::
F Sanity checks on (enables SLAB_DEBUG_CONSISTENCY_CHECKS
Sorry SLAB legacy issues)
Z Red zoning
P Poisoning (object and padding)
U User tracking (free and alloc)
T Trace (please only use on single slabs)
A Enable failslab filter mark for the cache
O Switch debugging off for caches that would have
caused higher minimum slab orders
- Switch all debugging off (useful if the kernel is
configured with CONFIG_SLUB_DEBUG_ON)
F.e. in order to boot just with sanity checks and red zoning one would specify::
slub_debug=FZ
Trying to find an issue in the dentry cache? Try::
slub_debug=,dentry
to only enable debugging on the dentry cache. You may use an asterisk at the
end of the slab name, in order to cover all slabs with the same prefix. For
example, here's how you can poison the dentry cache as well as all kmalloc
slabs::
slub_debug=P,kmalloc-*,dentry
Red zoning and tracking may realign the slab. We can just apply sanity checks
to the dentry cache with::
slub_debug=F,dentry
Debugging options may require the minimum possible slab order to increase as
a result of storing the metadata (for example, caches with PAGE_SIZE object
sizes). This has a higher liklihood of resulting in slab allocation errors
in low memory situations or if there's high fragmentation of memory. To
switch off debugging for such caches by default, use::
slub_debug=O
You can apply different options to different list of slab names, using blocks
of options. This will enable red zoning for dentry and user tracking for
kmalloc. All other slabs will not get any debugging enabled::
slub_debug=Z,dentry;U,kmalloc-*
You can also enable options (e.g. sanity checks and poisoning) for all caches
except some that are deemed too performance critical and don't need to be
debugged by specifying global debug options followed by a list of slab names
with "-" as options::
slub_debug=FZ;-,zs_handle,zspage
The state of each debug option for a slab can be found in the respective files
under::
/sys/kernel/slab/<slab name>/
If the file contains 1, the option is enabled, 0 means disabled. The debug
options from the ``slub_debug`` parameter translate to the following files::
F sanity_checks
Z red_zone
P poison
U store_user
T trace
A failslab
failslab file is writable, so writing 1 or 0 will enable or disable
the option at runtime. Write returns -EINVAL if cache is an alias.
Careful with tracing: It may spew out lots of information and never stop if
used on the wrong slab.
Slab merging
============
If no debug options are specified then SLUB may merge similar slabs together
in order to reduce overhead and increase cache hotness of objects.
``slabinfo -a`` displays which slabs were merged together.
Slab validation
===============
SLUB can validate all object if the kernel was booted with slub_debug. In
order to do so you must have the ``slabinfo`` tool. Then you can do
::
slabinfo -v
which will test all objects. Output will be generated to the syslog.
This also works in a more limited way if boot was without slab debug.
In that case ``slabinfo -v`` simply tests all reachable objects. Usually
these are in the cpu slabs and the partial slabs. Full slabs are not
tracked by SLUB in a non debug situation.
Getting more performance
========================
To some degree SLUB's performance is limited by the need to take the
list_lock once in a while to deal with partial slabs. That overhead is
governed by the order of the allocation for each slab. The allocations
can be influenced by kernel parameters:
.. slub_min_objects=x (default 4)
.. slub_min_order=x (default 0)
.. slub_max_order=x (default 3 (PAGE_ALLOC_COSTLY_ORDER))
``slub_min_objects``
allows to specify how many objects must at least fit into one
slab in order for the allocation order to be acceptable. In
general slub will be able to perform this number of
allocations on a slab without consulting centralized resources
(list_lock) where contention may occur.
``slub_min_order``
specifies a minimum order of slabs. A similar effect like
``slub_min_objects``.
``slub_max_order``
specified the order at which ``slub_min_objects`` should no
longer be checked. This is useful to avoid SLUB trying to
generate super large order pages to fit ``slub_min_objects``
of a slab cache with large object sizes into one high order
page. Setting command line parameter
``debug_guardpage_minorder=N`` (N > 0), forces setting
``slub_max_order`` to 0, what cause minimum possible order of
slabs allocation.
SLUB Debug output
=================
Here is a sample of slub debug output::
====================================================================
BUG kmalloc-8: Right Redzone overwritten
--------------------------------------------------------------------
INFO: 0xc90f6d28-0xc90f6d2b. First byte 0x00 instead of 0xcc
INFO: Slab 0xc528c530 flags=0x400000c3 inuse=61 fp=0xc90f6d58
INFO: Object 0xc90f6d20 @offset=3360 fp=0xc90f6d58
INFO: Allocated in get_modalias+0x61/0xf5 age=53 cpu=1 pid=554
Bytes b4 (0xc90f6d10): 00 00 00 00 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ
Object (0xc90f6d20): 31 30 31 39 2e 30 30 35 1019.005
Redzone (0xc90f6d28): 00 cc cc cc .
Padding (0xc90f6d50): 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ
[<c010523d>] dump_trace+0x63/0x1eb
[<c01053df>] show_trace_log_lvl+0x1a/0x2f
[<c010601d>] show_trace+0x12/0x14
[<c0106035>] dump_stack+0x16/0x18
[<c017e0fa>] object_err+0x143/0x14b
[<c017e2cc>] check_object+0x66/0x234
[<c017eb43>] __slab_free+0x239/0x384
[<c017f446>] kfree+0xa6/0xc6
[<c02e2335>] get_modalias+0xb9/0xf5
[<c02e23b7>] dmi_dev_uevent+0x27/0x3c
[<c027866a>] dev_uevent+0x1ad/0x1da
[<c0205024>] kobject_uevent_env+0x20a/0x45b
[<c020527f>] kobject_uevent+0xa/0xf
[<c02779f1>] store_uevent+0x4f/0x58
[<c027758e>] dev_attr_store+0x29/0x2f
[<c01bec4f>] sysfs_write_file+0x16e/0x19c
[<c0183ba7>] vfs_write+0xd1/0x15a
[<c01841d7>] sys_write+0x3d/0x72
[<c0104112>] sysenter_past_esp+0x5f/0x99
[<b7f7b410>] 0xb7f7b410
=======================
FIX kmalloc-8: Restoring Redzone 0xc90f6d28-0xc90f6d2b=0xcc
If SLUB encounters a corrupted object (full detection requires the kernel
to be booted with slub_debug) then the following output will be dumped
into the syslog:
1. Description of the problem encountered
This will be a message in the system log starting with::
===============================================
BUG <slab cache affected>: <What went wrong>
-----------------------------------------------
INFO: <corruption start>-<corruption_end> <more info>
INFO: Slab <address> <slab information>
INFO: Object <address> <object information>
INFO: Allocated in <kernel function> age=<jiffies since alloc> cpu=<allocated by
cpu> pid=<pid of the process>
INFO: Freed in <kernel function> age=<jiffies since free> cpu=<freed by cpu>
pid=<pid of the process>
(Object allocation / free information is only available if SLAB_STORE_USER is
set for the slab. slub_debug sets that option)
2. The object contents if an object was involved.
Various types of lines can follow the BUG SLUB line:
Bytes b4 <address> : <bytes>
Shows a few bytes before the object where the problem was detected.
Can be useful if the corruption does not stop with the start of the
object.
Object <address> : <bytes>
The bytes of the object. If the object is inactive then the bytes
typically contain poison values. Any non-poison value shows a
corruption by a write after free.
Redzone <address> : <bytes>
The Redzone following the object. The Redzone is used to detect
writes after the object. All bytes should always have the same
value. If there is any deviation then it is due to a write after
the object boundary.
(Redzone information is only available if SLAB_RED_ZONE is set.
slub_debug sets that option)
Padding <address> : <bytes>
Unused data to fill up the space in order to get the next object
properly aligned. In the debug case we make sure that there are
at least 4 bytes of padding. This allows the detection of writes
before the object.
3. A stackdump
The stackdump describes the location where the error was detected. The cause
of the corruption is may be more likely found by looking at the function that
allocated or freed the object.
4. Report on how the problem was dealt with in order to ensure the continued
operation of the system.
These are messages in the system log beginning with::
FIX <slab cache affected>: <corrective action taken>
In the above sample SLUB found that the Redzone of an active object has
been overwritten. Here a string of 8 characters was written into a slab that
has the length of 8 characters. However, a 8 character string needs a
terminating 0. That zero has overwritten the first byte of the Redzone field.
After reporting the details of the issue encountered the FIX SLUB message
tells us that SLUB has restored the Redzone to its proper value and then
system operations continue.
Emergency operations
====================
Minimal debugging (sanity checks alone) can be enabled by booting with::
slub_debug=F
This will be generally be enough to enable the resiliency features of slub
which will keep the system running even if a bad kernel component will
keep corrupting objects. This may be important for production systems.
Performance will be impacted by the sanity checks and there will be a
continual stream of error messages to the syslog but no additional memory
will be used (unlike full debugging).
No guarantees. The kernel component still needs to be fixed. Performance
may be optimized further by locating the slab that experiences corruption
and enabling debugging only for that cache
I.e.::
slub_debug=F,dentry
If the corruption occurs by writing after the end of the object then it
may be advisable to enable a Redzone to avoid corrupting the beginning
of other objects::
slub_debug=FZ,dentry
Extended slabinfo mode and plotting
===================================
The ``slabinfo`` tool has a special 'extended' ('-X') mode that includes:
- Slabcache Totals
- Slabs sorted by size (up to -N <num> slabs, default 1)
- Slabs sorted by loss (up to -N <num> slabs, default 1)
Additionally, in this mode ``slabinfo`` does not dynamically scale
sizes (G/M/K) and reports everything in bytes (this functionality is
also available to other slabinfo modes via '-B' option) which makes
reporting more precise and accurate. Moreover, in some sense the `-X'
mode also simplifies the analysis of slabs' behaviour, because its
output can be plotted using the ``slabinfo-gnuplot.sh`` script. So it
pushes the analysis from looking through the numbers (tons of numbers)
to something easier -- visual analysis.
To generate plots:
a) collect slabinfo extended records, for example::
while [ 1 ]; do slabinfo -X >> FOO_STATS; sleep 1; done
b) pass stats file(-s) to ``slabinfo-gnuplot.sh`` script::
slabinfo-gnuplot.sh FOO_STATS [FOO_STATS2 .. FOO_STATSN]
The ``slabinfo-gnuplot.sh`` script will pre-processes the collected records
and generates 3 png files (and 3 pre-processing cache files) per STATS
file:
- Slabcache Totals: FOO_STATS-totals.png
- Slabs sorted by size: FOO_STATS-slabs-by-size.png
- Slabs sorted by loss: FOO_STATS-slabs-by-loss.png
Another use case, when ``slabinfo-gnuplot.sh`` can be useful, is when you
need to compare slabs' behaviour "prior to" and "after" some code
modification. To help you out there, ``slabinfo-gnuplot.sh`` script
can 'merge' the `Slabcache Totals` sections from different
measurements. To visually compare N plots:
a) Collect as many STATS1, STATS2, .. STATSN files as you need::
while [ 1 ]; do slabinfo -X >> STATS<X>; sleep 1; done
b) Pre-process those STATS files::
slabinfo-gnuplot.sh STATS1 STATS2 .. STATSN
c) Execute ``slabinfo-gnuplot.sh`` in '-t' mode, passing all of the
generated pre-processed \*-totals::
slabinfo-gnuplot.sh -t STATS1-totals STATS2-totals .. STATSN-totals
This will produce a single plot (png file).
Plots, expectedly, can be large so some fluctuations or small spikes
can go unnoticed. To deal with that, ``slabinfo-gnuplot.sh`` has two
options to 'zoom-in'/'zoom-out':
a) ``-s %d,%d`` -- overwrites the default image width and height
b) ``-r %d,%d`` -- specifies a range of samples to use (for example,
in ``slabinfo -X >> FOO_STATS; sleep 1;`` case, using a ``-r
40,60`` range will plot only samples collected between 40th and
60th seconds).
DebugFS files for SLUB
======================
For more information about current state of SLUB caches with the user tracking
debug option enabled, debugfs files are available, typically under
/sys/kernel/debug/slab/<cache>/ (created only for caches with enabled user
tracking). There are 2 types of these files with the following debug
information:
1. alloc_traces::
Prints information about unique allocation traces of the currently
allocated objects. The output is sorted by frequency of each trace.
Information in the output:
Number of objects, allocating function, possible memory wastage of
kmalloc objects(total/per-object), minimal/average/maximal jiffies
since alloc, pid range of the allocating processes, cpu mask of
allocating cpus, numa node mask of origins of memory, and stack trace.
Example:::
338 pci_alloc_dev+0x2c/0xa0 waste=521872/1544 age=290837/291891/293509 pid=1 cpus=106 nodes=0-1
__kmem_cache_alloc_node+0x11f/0x4e0
kmalloc_trace+0x26/0xa0
pci_alloc_dev+0x2c/0xa0
pci_scan_single_device+0xd2/0x150
pci_scan_slot+0xf7/0x2d0
pci_scan_child_bus_extend+0x4e/0x360
acpi_pci_root_create+0x32e/0x3b0
pci_acpi_scan_root+0x2b9/0x2d0
acpi_pci_root_add.cold.11+0x110/0xb0a
acpi_bus_attach+0x262/0x3f0
device_for_each_child+0xb7/0x110
acpi_dev_for_each_child+0x77/0xa0
acpi_bus_attach+0x108/0x3f0
device_for_each_child+0xb7/0x110
acpi_dev_for_each_child+0x77/0xa0
acpi_bus_attach+0x108/0x3f0
2. free_traces::
Prints information about unique freeing traces of the currently allocated
objects. The freeing traces thus come from the previous life-cycle of the
objects and are reported as not available for objects allocated for the first
time. The output is sorted by frequency of each trace.
Information in the output:
Number of objects, freeing function, minimal/average/maximal jiffies since free,
pid range of the freeing processes, cpu mask of freeing cpus, and stack trace.
Example:::
1980 <not-available> age=4294912290 pid=0 cpus=0
51 acpi_ut_update_ref_count+0x6a6/0x782 age=236886/237027/237772 pid=1 cpus=1
kfree+0x2db/0x420
acpi_ut_update_ref_count+0x6a6/0x782
acpi_ut_update_object_reference+0x1ad/0x234
acpi_ut_remove_reference+0x7d/0x84
acpi_rs_get_prt_method_data+0x97/0xd6
acpi_get_irq_routing_table+0x82/0xc4
acpi_pci_irq_find_prt_entry+0x8e/0x2e0
acpi_pci_irq_lookup+0x3a/0x1e0
acpi_pci_irq_enable+0x77/0x240
pcibios_enable_device+0x39/0x40
do_pci_enable_device.part.0+0x5d/0xe0
pci_enable_device_flags+0xfc/0x120
pci_enable_device+0x13/0x20
virtio_pci_probe+0x9e/0x170
local_pci_probe+0x48/0x80
pci_device_probe+0x105/0x1c0
Christoph Lameter, May 30, 2007
Sergey Senozhatsky, October 23, 2015