Re: [PATCH v20 02/20] mm/memcg: bail early from swap accounting if memcg disabled

[Johannes Weiner]

On Thu, Oct 29, 2020 at 06:44:47PM +0800, Alex Shi wrote:
> If we disabled memcg by cgroup_disable=memory, page->memcg will be NULL
> and so the charge is skipped and that will trigger a warning like below.
> Let's return from the funcs earlier.
> 
>  anon flags:0x5005b48008000d(locked|uptodate|dirty|swapbacked)
>  raw: 005005b48008000d dead000000000100 dead000000000122 ffff8897c7c76ad1
>  raw: 0000000000000022 0000000000000000 0000000200000000 0000000000000000
>  page dumped because: VM_WARN_ON_ONCE_PAGE(!memcg)
> ...
>  RIP: 0010:vprintk_emit+0x1f7/0x260
>  Code: 00 84 d2 74 72 0f b6 15 27 58 64 01 48 c7 c0 00 d4 72 82 84 d2 74 09 f3 90 0f b6 10 84 d2 75 f7 e8 de 0d 00 00 4c 89 e7 57 9d <0f> 1f 44 00 00 e9 62 ff ff ff 80 3d 88 c9 3a 01 00 0f 85 54 fe ff
>  RSP: 0018:ffffc9000faab358 EFLAGS: 00000202
>  RAX: ffffffff8272d400 RBX: 000000000000005e RCX: ffff88afd80d0040
>  RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000202
>  RBP: ffffc9000faab3a8 R08: ffffffff8272d440 R09: 0000000000022480
>  R10: 00120c77be68bfac R11: 0000000000cd7568 R12: 0000000000000202
>  R13: 0057ffffc0080005 R14: ffffffff820a0130 R15: ffffc9000faab3e8
>  ? vprintk_emit+0x140/0x260
>  vprintk_default+0x1a/0x20
>  vprintk_func+0x4f/0xc4
>  ? vprintk_func+0x4f/0xc4
>  printk+0x53/0x6a
>  ? xas_load+0xc/0x80
>  __dump_page.cold.6+0xff/0x4ee
>  ? xas_init_marks+0x23/0x50
>  ? xas_store+0x30/0x40
>  ? free_swap_slot+0x43/0xd0
>  ? put_swap_page+0x119/0x320
>  ? update_load_avg+0x82/0x580
>  dump_page+0x9/0xb
>  mem_cgroup_try_charge_swap+0x16e/0x1d0
>  get_swap_page+0x130/0x210
>  add_to_swap+0x41/0xc0
>  shrink_page_list+0x99e/0xdf0
>  shrink_inactive_list+0x199/0x360
>  shrink_lruvec+0x40d/0x650
>  ? _cond_resched+0x14/0x30
>  ? _cond_resched+0x14/0x30
>  shrink_node+0x226/0x6e0
>  do_try_to_free_pages+0xd0/0x400
>  try_to_free_pages+0xef/0x130
>  __alloc_pages_slowpath.constprop.127+0x38d/0xbd0
>  ? ___slab_alloc+0x31d/0x6f0
>  __alloc_pages_nodemask+0x27f/0x2c0
>  alloc_pages_vma+0x75/0x220
>  shmem_alloc_page+0x46/0x90
>  ? release_pages+0x1ae/0x410
>  shmem_alloc_and_acct_page+0x77/0x1c0
>  shmem_getpage_gfp+0x162/0x910
>  shmem_fault+0x74/0x210
>  ? filemap_map_pages+0x29c/0x410
>  __do_fault+0x37/0x190
>  handle_mm_fault+0x120a/0x1770
>  exc_page_fault+0x251/0x450
>  ? asm_exc_page_fault+0x8/0x30
>  asm_exc_page_fault+0x1e/0x30
> 
> Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
> Reviewed-by: Roman Gushchin <guro@xxxxxx>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: cgroups@xxxxxxxxxxxxxxx
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx

Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>

This should go in before the previous patch that adds the WARN for it.