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
