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Subject: Re: [PATCH] mm/memcg: remove useless check on page->mem_cgroup
From:   Alex Shi <alex.shi@linux.alibaba.com>
To:     Michal Hocko <mhocko@suse.com>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        cgroups@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
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Date:   Wed, 5 Aug 2020 21:02:30 +0800
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在 2020/8/5 下午8:28, Alex Shi 写道:
> The last patch has a problem on define. this version could fix it.
> 
> BTW, I see some !memcg happens when MEMCG compilered but disabled by cgroup_disable
> 
> 
> [   94.657666] ---[ end trace f1f34bfc3b32ed2f ]---
> [   95.138995] anon flags: 0x5005b48008000d(locked|uptodate|dirty|swapbacked)
> [   95.146220] raw: 005005b48008000d dead000000000100 dead000000000122 ffff8897c7c76ad1
> [   95.154549] raw: 0000000000000022 0000000000000000 0000000200000000 0000000000000000
> [   95.162876] page dumped because: VM_WARN_ON_ONCE_PAGE(!memcg)
> 
> 

The following patch may helpful.

From 8bfb26a2e37e08dc61d20212bcfa5812a367ba94 Mon Sep 17 00:00:00 2001
From: Alex Shi <alex.shi@linux.alibaba.com>
Date: Wed, 5 Aug 2020 20:32:12 +0800
Subject: [PATCH] mm/memcg: don't try charge swap if memcg disabled

If we disabled memcg by cgroup_disable=memory, the swap charges are
still called. Let's return from the funcs earlier and keep WARN_ON
monitor.

Signed-off-by: Alex Shi <alex.shi@linux.alibaba.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 cb07a48d53aa..65f2b42d25af 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -7163,6 +7163,9 @@ 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;
 
@@ -7228,6 +7231,9 @@ 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