Re: [PATCH] mm/memcg: remove useless check on page->mem_cgroup

From: Roman Gushchin <guro@fb.com>
To: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Michal Hocko <mhocko@suse.com>,
	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>
Subject: Re: [PATCH] mm/memcg: remove useless check on page->mem_cgroup
Date: Sat, 8 Aug 2020 14:43:06 -0700	[thread overview]
Message-ID: <20200808214306.GA1409287@carbon.dhcp.thefacebook.com> (raw)
In-Reply-To: <4740bac1-72f6-a640-ab6a-a8801e68c27a@linux.alibaba.com>

On Sat, Aug 08, 2020 at 09:22:29PM +0800, Alex Shi wrote:
> 
> 
> 在 2020/8/5 下午9:02, Alex Shi 写道:
> > 
> > 
> > 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.
> 
> Any comments for the 2 patches?
> 
> Thanks
> Alex
> 
> > 
> > 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;
> >  
> > 

Hi Alex,

this patch looks good to me. Please, feel free to add
Reviewed-by: Roman Gushchin <guro@fb.com>

What's the second patch?

Thanks!