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Subject[PATCH v18 02/32] mm/memcg: bail out early from swap accounting when memcg is disabled
Date
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@linux.alibaba.com>
Reviewed-by: Roman Gushchin <guro@fb.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: cgroups@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
---
mm/memcontrol.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ffdc622e5828..5974b449d783 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -7098,6 +7098,9 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
VM_BUG_ON_PAGE(PageLRU(page), page);
VM_BUG_ON_PAGE(page_count(page), page);

+ if (mem_cgroup_disabled())
+ return;
+
if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
return;

@@ -7163,6 +7166,9 @@ int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
struct mem_cgroup *memcg;
unsigned short oldid;

+ if (mem_cgroup_disabled())
+ return 0;
+
if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
return 0;

--
1.8.3.1
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