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 offlined 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 offlined 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 62760, ts 119274296592 ns, free_ts 118989764823 ns
PFN 1273412 type Movable Block 2487 type Movable Flags 0x17ffffc00c001c(uptodate|dirty|lru|reclaim|swapbacked|node=0|zone=2|lastcpupid=0x1fffff)
prep_new_page+0x8e/0xb0
get_page_from_freelist+0xc4d/0xe50
__alloc_pages+0x172/0x320
alloc_pages_vma+0x84/0x230
shmem_alloc_page+0x3f/0x90
shmem_alloc_and_acct_page+0x76/0x1c0
shmem_getpage_gfp+0x48d/0x890
shmem_write_begin+0x36/0xc0
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 offlined memcg libpod-conmon-e59cc83faf807bacc61223fec6a80c1540ebe8f83c802870c6af4708d58f77ea
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.
Waiman Long (2):
mm/page_owner: Introduce SNPRINTF() macro that includes length error
check
mm/page_owner: Dump memcg information
mm/page_owner.c | 76 ++++++++++++++++++++++++++++++++-----------------
1 file changed, 50 insertions(+), 26 deletions(-)
--
2.27.0
