| Message ID | 20240215215907.20121-1-osalvador@suse.de (mailing list archive) |
|---|---|
| Headers | show |
| Series | page_owner: print stacks and their outstanding allocations | expand |
On Thu, Feb 15, 2024 at 10:57 PM Oscar Salvador <osalvador@suse.de> 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@gmail.com>
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(-)