[PATCH v2 0/3] mm/page_owner: Extend page_owner to show memcg information

[Waiman Long <longman@redhat.com>]

 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 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 (3):
  lib/vsprintf: Avoid redundant work with 0 size
  mm/page_owner: Use scnprintf() to avoid excessive buffer overrun check
  mm/page_owner: Dump memcg information

 lib/vsprintf.c  |  8 +++++---
 mm/page_owner.c | 45 ++++++++++++++++++++++++++++++++++-----------
 2 files changed, 39 insertions(+), 14 deletions(-)

-- 
2.27.0