Changes v5 -> v6:
- Rebase on top of v6.7-rc1
- Move stack_record struct to the header
- Addressed feedback from Vlastimil
(some code tweaks and changelogs suggestions)
Changes v4 -> v5:
- Addressed feedback from Alexander Potapenko
Changes v3 -> v4:
- Rebase (long time has passed)
- Use boolean instead of enum for action by Alexander Potapenko
- (I left some feedback untouched because it's been long and
would like to discuss it here now instead of re-vamping
and old thread)
Changes v2 -> v3:
- Replace interface in favor of seq operations (suggested by Vlastimil)
- Use debugfs interface to store/read valued (suggested by Ammar)
Hi,
page_owner is a great debug functionality tool that lets us know
about all pages that have been allocated/freed and their stacktrace.
This comes very handy when one has to debug memory leaks, since with
some scripting we can see outstanding allocations, which might end up
pointing to a leak.
In my experience, that is one of the most useful cases, but it can get
really tedious to screen through all pages and try to reconstruct the
stack <-> allocated/freed relationship. There is a lot of noise
to cancel off.
This patchset aims to ease that by adding a new functionality into page_owner.
What this does is to create a new read-only file "page_owner_stacks",
which prints out only the stacktraces followed by their outstanding
number of allocations (being that the times the stacktrace has allocated
but not freed yet).
This lets us have a clear overview of stacks <-> allocated/freed relationship
without the need to fiddle with pages and trying to match free stacktraces
with allocated stacktraces.
This is achieved by adding a new refcount_t field in the stack_record struct,
incrementing that refcount_t everytime the same stacktrace allocates,
and decrementing it when it frees a page. Details can be seen in the
respective patches.
We also create another file called "page_owner_threshold", which let us
specify a threshold, so when reading from "page_owner_stacks",
we will only see those stacktraces which counting goes beyond the
threshold we specified.
A PoC can be found below:
# cat /sys/kernel/debug/page_owner_threshold
0
# cat /sys/kernel/debug/page_owner_stacks > stacks_full.txt
# head -32 stacks_full.txt
prep_new_page+0x10d/0x180
get_page_from_freelist+0x1bd6/0x1e10
__alloc_pages+0x194/0x360
alloc_page_interleave+0x13/0x90
new_slab+0x31d/0x530
___slab_alloc+0x5d7/0x720
__slab_alloc.isra.85+0x4a/0x90
kmem_cache_alloc+0x455/0x4a0
acpi_ps_alloc_op+0x57/0x8f
acpi_ps_create_scope_op+0x12/0x23
acpi_ps_execute_method+0x102/0x2c1
acpi_ns_evaluate+0x343/0x4da
acpi_evaluate_object+0x1cb/0x392
acpi_run_osc+0x135/0x260
acpi_init+0x165/0x4ed
do_one_initcall+0x3e/0x200
stack count: 2
free_pcp_prepare+0x287/0x5c0
free_unref_page+0x1c/0xd0
__mmdrop+0x50/0x160
finish_task_switch+0x249/0x2b0
__schedule+0x2c3/0x960
schedule+0x44/0xb0
futex_wait_queue+0x70/0xd0
futex_wait+0x160/0x250
do_futex+0x11c/0x1b0
__x64_sys_futex+0x5e/0x1d0
do_syscall_64+0x37/0x90
entry_SYSCALL_64_after_hwframe+0x63/0xcd
stack count: 1
# echo 10000 > /sys/kernel/debug/page_owner_threshold
# cat /sys/kernel/debug/page_owner_stacks > stacks_10000.txt
# cat stacks_10000.txt
prep_new_page+0x10d/0x180
get_page_from_freelist+0x1bd6/0x1e10
__alloc_pages+0x194/0x360
folio_alloc+0x17/0x40
page_cache_ra_unbounded+0x96/0x170
filemap_get_pages+0x23d/0x5e0
filemap_read+0xbf/0x3a0
__kernel_read+0x136/0x2f0
kernel_read_file+0x197/0x2d0
kernel_read_file_from_fd+0x54/0x90
__do_sys_finit_module+0x89/0x120
do_syscall_64+0x37/0x90
entry_SYSCALL_64_after_hwframe+0x63/0xcd
stack count: 36195
prep_new_page+0x10d/0x180
get_page_from_freelist+0x1bd6/0x1e10
__alloc_pages+0x194/0x360
folio_alloc+0x17/0x40
page_cache_ra_unbounded+0x96/0x170
filemap_get_pages+0x23d/0x5e0
filemap_read+0xbf/0x3a0
new_sync_read+0x106/0x180
vfs_read+0x16f/0x190
ksys_read+0xa5/0xe0
do_syscall_64+0x37/0x90
entry_SYSCALL_64_after_hwframe+0x63/0xcd
stack count: 44484
prep_new_page+0x10d/0x180
get_page_from_freelist+0x1bd6/0x1e10
__alloc_pages+0x194/0x360
folio_alloc+0x17/0x40
page_cache_ra_unbounded+0x96/0x170
filemap_get_pages+0xdd/0x5e0
filemap_read+0xbf/0x3a0
new_sync_read+0x106/0x180
vfs_read+0x16f/0x190
ksys_read+0xa5/0xe0
do_syscall_64+0x37/0x90
entry_SYSCALL_64_after_hwframe+0x63/0xcd
stack count: 17874
Oscar Salvador (4):
lib/stackdepot: Add a refcount field in stack_record
lib/stackdepot: Move stack_record struct definition into the header
mm,page_owner: Add page_owner_stacks file to print out only stacks and
their counter
mm,page_owner: Filter out stacks by a threshold counter
include/linux/stackdepot.h | 38 ++++++++++++
lib/stackdepot.c | 114 ++++++++++++++++++++++--------------
mm/page_owner.c | 115 +++++++++++++++++++++++++++++++++++++
3 files changed, 224 insertions(+), 43 deletions(-)
--
2.42.0
On 11/20/23 09:42, Oscar Salvador wrote:
> Changes v5 -> v6:
> - Rebase on top of v6.7-rc1
Hi,
I think at this point it would be better to rebase on top of
https://lore.kernel.org/all/[email protected]/
which already contains the refcount field in stack_record.
(and maybe help with the review of that series as well? Hopefully it can get
to mm/unstable and -next towards 6.8 soon :)
Vlastimil
On Mon, Nov 20, 2023 at 10:07 AM Vlastimil Babka <[email protected]> wrote:
>
> On 11/20/23 09:42, Oscar Salvador wrote:
> > Changes v5 -> v6:
> > - Rebase on top of v6.7-rc1
>
> Hi,
>
> I think at this point it would be better to rebase on top of
> https://lore.kernel.org/all/[email protected]/
> which already contains the refcount field in stack_record.
> (and maybe help with the review of that series as well? Hopefully it can get
> to mm/unstable and -next towards 6.8 soon :)
Yes, please; I just mailed a v4 that is based on v6.7-rc2:
https://lore.kernel.org/linux-mm/[email protected]/T/#t
You should also be able to use the new
stack_depot_save_flags(STACK_DEPOT_FLAG_GET)/stack_depot_put API to
keep only the relevant stack traces.
Thank you!