On Thu, Feb 15, 2024 at 10:57 PM Oscar Salvador <osalvador@xxxxxxx> wrote:
>
> Changes v9 -> v10
> - Fix unwanted change in patch#2
> - Collect Acked-by and Reviewed-by from Marco and Vlastimil
> for the missing patches
> - Fix stack_record count by substracting 1 in stack_print by Vlastimil
>
> Changes v8 -> v9
> - Fix handle-0 for the very first stack_record entry
> - Collect Acked-by and Reviewed-by from Marco and Vlastimil
> - Adressed feedback from Marco and Vlastimil
> - stack_print() no longer allocates a memory buffer, prints directly
> using seq_printf: by Vlastimil
> - Added two static struct stack for dummy_handle and faiure_handle
> - add_stack_record_to_list() now filters out the gfp_mask the same way
> stackdepot does, for consistency
> - Rename set_threshold to count_threshold
>
> Changes v7 -> v8
> - Rebased on top of -next
> - page_owner maintains its own stack_records list now
> - Kill auxiliary stackdepot function to traverse buckets
> - page_owner_stacks is now a directory with 'show_stacks'
> and 'set_threshold'
> - Update Documentation/mm/page_owner.rst
> - Adressed feedback from Marco
>
> Changes v6 -> v7:
> - Rebased on top of Andrey Konovalov's libstackdepot patchset
> - Reformulated the changelogs
>
> 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)
>
>
> page_owner is a great debug functionality tool that lets us know
> about all pages that have been allocated/freed and their specific
> stacktrace.
> This comes very handy when debugging memory leaks, since with
> some scripting we can see the outstanding allocations, which might point
> to a memory 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, becoming most of the time a
> daunting and slow process when we have tons of allocation/free operations.
>
> This patchset aims to ease that by adding a new functionality into
> page_owner.
> This functionality creates a new directory called 'page_owner_stacks'
> under 'sys/kernel//debug' with a read-only file called 'show_stacks',
> which prints out all the stacks followed by their outstanding number
> of allocations (being that the times the stacktrace has allocated
> but not freed yet).
> This gives us a clear and a quick overview of stacks <-> allocated/free.
>
> We take advantage of the new refcount_f field that stack_record struct
> gained, and increment/decrement the stack refcount on every
> __set_page_owner() (alloc operation) and __reset_page_owner (free operation)
> call.
>
> Unfortunately, we cannot use the new stackdepot api
> STACK_DEPOT_FLAG_GET because it does not fulfill page_owner needs,
> meaning we would have to special case things, at which point
> makes more sense for page_owner to do its own {dec,inc}rementing
> of the stacks.
> E.g: Using STACK_DEPOT_FLAG_PUT, once the refcount reaches 0,
> such stack gets evicted, so page_owner would lose information.
>
> This patch also creates a new file called 'set_threshold' within
> 'page_owner_stacks' directory, and by writing a value to it, the stacks
> which refcount is below such value will be filtered out.
>
> A PoC can be found below:
>
> # cat /sys/kernel/debug/page_owner_stacks/show_stacks > page_owner_full_stacks.txt
> # head -40 page_owner_full_stacks.txt
> prep_new_page+0xa9/0x120
> get_page_from_freelist+0x801/0x2210
> __alloc_pages+0x18b/0x350
> alloc_pages_mpol+0x91/0x1f0
> folio_alloc+0x14/0x50
> filemap_alloc_folio+0xb2/0x100
> page_cache_ra_unbounded+0x96/0x180
> filemap_get_pages+0xfd/0x590
> filemap_read+0xcc/0x330
> blkdev_read_iter+0xb8/0x150
> vfs_read+0x285/0x320
> ksys_read+0xa5/0xe0
> do_syscall_64+0x80/0x160
> entry_SYSCALL_64_after_hwframe+0x6e/0x76
> stack_count: 521
>
>
>
> prep_new_page+0xa9/0x120
> get_page_from_freelist+0x801/0x2210
> __alloc_pages+0x18b/0x350
> alloc_pages_mpol+0x91/0x1f0
> folio_alloc+0x14/0x50
> filemap_alloc_folio+0xb2/0x100
> __filemap_get_folio+0x14a/0x490
> ext4_write_begin+0xbd/0x4b0 [ext4]
> generic_perform_write+0xc1/0x1e0
> ext4_buffered_write_iter+0x68/0xe0 [ext4]
> ext4_file_write_iter+0x70/0x740 [ext4]
> vfs_write+0x33d/0x420
> ksys_write+0xa5/0xe0
> do_syscall_64+0x80/0x160
> entry_SYSCALL_64_after_hwframe+0x6e/0x76
> stack_count: 4609
> ...
> ...
>
> # echo 5000 > /sys/kernel/debug/page_owner_stacks/set_threshold
> # cat /sys/kernel/debug/page_owner_stacks/show_stacks > page_owner_full_stacks_5000.txt
> # head -40 page_owner_full_stacks_5000.txt
> prep_new_page+0xa9/0x120
> get_page_from_freelist+0x801/0x2210
> __alloc_pages+0x18b/0x350
> alloc_pages_mpol+0x91/0x1f0
> folio_alloc+0x14/0x50
> filemap_alloc_folio+0xb2/0x100
> __filemap_get_folio+0x14a/0x490
> ext4_write_begin+0xbd/0x4b0 [ext4]
> generic_perform_write+0xc1/0x1e0
> ext4_buffered_write_iter+0x68/0xe0 [ext4]
> ext4_file_write_iter+0x70/0x740 [ext4]
> vfs_write+0x33d/0x420
> ksys_pwrite64+0x75/0x90
> do_syscall_64+0x80/0x160
> entry_SYSCALL_64_after_hwframe+0x6e/0x76
> stack_count: 6781
>
>
>
> prep_new_page+0xa9/0x120
> get_page_from_freelist+0x801/0x2210
> __alloc_pages+0x18b/0x350
> pcpu_populate_chunk+0xec/0x350
> pcpu_balance_workfn+0x2d1/0x4a0
> process_scheduled_works+0x84/0x380
> worker_thread+0x12a/0x2a0
> kthread+0xe3/0x110
> ret_from_fork+0x30/0x50
> ret_from_fork_asm+0x1b/0x30
> stack_count: 8641
>
> Oscar Salvador (7):
> lib/stackdepot: Fix first entry having a 0-handle
> lib/stackdepot: Move stack_record struct definition into the header
> mm,page_owner: Maintain own list of stack_records structs
> mm,page_owner: Implement the tracking of the stacks count
> mm,page_owner: Display all stacks and their count
> mm,page_owner: Filter out stacks by a threshold
> mm,page_owner: Update Documentation regarding page_owner_stacks
>
> Documentation/mm/page_owner.rst | 45 +++++++
> include/linux/stackdepot.h | 58 +++++++++
> lib/stackdepot.c | 65 +++--------
> mm/page_owner.c | 200 +++++++++++++++++++++++++++++++-
> 4 files changed, 318 insertions(+), 50 deletions(-)
>
> --
> 2.43.0
>
Acked-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>
