On Wed, Feb 02, 2022 at 03:30:32PM -0500, Waiman Long wrote:
> v4:
> - Take rcu_read_lock() when memcg is being accessed as suggested by
> Michal.
> - Make print_page_owner_memcg() return the new offset into the buffer
> and put CONFIG_MEMCG block inside as suggested by Mike.
> - Directly use TASK_COMM_LEN as length of name buffer as suggested by
> Roman.
>
> v3:
> - Add unlikely() to patch 1 and clarify that -1 will not be returned.
> - Use a helper function to print out memcg information in patch 3.
> - Add a new patch 4 to store task command name in page_owner
> structure.
>
> v2:
> - Remove the SNPRINTF() macro as suggested by Ira and use scnprintf()
> instead to remove some buffer overrun checks.
> - Add a patch to optimize vscnprintf with a size parameter of 0.
>
> While debugging the constant increase in percpu memory consumption on
> a system that spawned large number of containers, it was found that a
> lot of offline mem_cgroup structures remained in place without being
> freed. Further investigation indicated that those mem_cgroup structures
> were pinned by some pages.
>
> In order to find out what those pages are, the existing page_owner
> debugging tool is extended to show memory cgroup information and whether
> those memcgs are offline or not. With the enhanced page_owner tool,
> the following is a typical page that pinned the mem_cgroup structure
> in my test case:
>
> Page allocated via order 0, mask 0x1100cca(GFP_HIGHUSER_MOVABLE), pid 162970 (podman), ts 1097761405537 ns, free_ts 1097760838089 ns
> PFN 1925700 type Movable Block 3761 type Movable Flags 0x17ffffc00c001c(uptodate|dirty|lru|reclaim|swapbacked|node=0|zone=2|lastcpupid=0x1fffff)
> prep_new_page+0xac/0xe0
> get_page_from_freelist+0x1327/0x14d0
> __alloc_pages+0x191/0x340
> alloc_pages_vma+0x84/0x250
> shmem_alloc_page+0x3f/0x90
> shmem_alloc_and_acct_page+0x76/0x1c0
> shmem_getpage_gfp+0x281/0x940
> shmem_write_begin+0x36/0xe0
> generic_perform_write+0xed/0x1d0
> __generic_file_write_iter+0xdc/0x1b0
> generic_file_write_iter+0x5d/0xb0
> new_sync_write+0x11f/0x1b0
> vfs_write+0x1ba/0x2a0
> ksys_write+0x59/0xd0
> do_syscall_64+0x37/0x80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
> Charged to offline memcg libpod-conmon-15e4f9c758422306b73b2dd99f9d50a5ea53cbb16b4a13a2c2308a4253cc0ec8.
>
> So the page was not freed because it was part of a shmem segment. That
> is useful information that can help users to diagnose similar problems.
>
> With cgroup v1, /proc/cgroups can be read to find out the total number
> of memory cgroups (online + offline). With cgroup v2, the cgroup.stat of
> the root cgroup can be read to find the number of dying cgroups (most
> likely pinned by dying memcgs).
>
> The page_owner feature is not supposed to be enabled for production
> system due to its memory overhead. However, if it is suspected that
> dying memcgs are increasing over time, a test environment with page_owner
> enabled can then be set up with appropriate workload for further analysis
> on what may be causing the increasing number of dying memcgs.
>
> Waiman Long (4):
> lib/vsprintf: Avoid redundant work with 0 size
> mm/page_owner: Use scnprintf() to avoid excessive buffer overrun check
> mm/page_owner: Print memcg information
> mm/page_owner: Record task command name
>
> lib/vsprintf.c | 8 +++---
> mm/page_owner.c | 70 ++++++++++++++++++++++++++++++++++++++-----------
> 2 files changed, 60 insertions(+), 18 deletions(-)
>
> --
> 2.27.0
>
Thank you, Waiman.
Acked-by: Rafael Aquini <[email protected]>