linux-kernel - Re: [PATCH 1/7] mm: memcontrol: charge swap to cgroup2

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Date:	Fri, 11 Dec 2015 10:39:37 +0300
From:	Vladimir Davydov <vdavydov@...tuozzo.com>
To:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/7] mm: memcontrol: charge swap to cgroup2

On Fri, Dec 11, 2015 at 11:48:57AM +0900, Kamezawa Hiroyuki wrote:
> On 2015/12/10 20:39, Vladimir Davydov wrote:
> > In the legacy hierarchy we charge memsw, which is dubious, because:
> > 
> >   - memsw.limit must be >= memory.limit, so it is impossible to limit
> >     swap usage less than memory usage. Taking into account the fact that
> >     the primary limiting mechanism in the unified hierarchy is
> >     memory.high while memory.limit is either left unset or set to a very
> >     large value, moving memsw.limit knob to the unified hierarchy would
> >     effectively make it impossible to limit swap usage according to the
> >     user preference.
> > 
> >   - memsw.usage != memory.usage + swap.usage, because a page occupying
> >     both swap entry and a swap cache page is charged only once to memsw
> >     counter. As a result, it is possible to effectively eat up to
> >     memory.limit of memory pages *and* memsw.limit of swap entries, which
> >     looks unexpected.
> > 
> > That said, we should provide a different swap limiting mechanism for
> > cgroup2.
> > 
> > This patch adds mem_cgroup->swap counter, which charges the actual
> > number of swap entries used by a cgroup. It is only charged in the
> > unified hierarchy, while the legacy hierarchy memsw logic is left
> > intact.
> > 
> > The swap usage can be monitored using new memory.swap.current file and
> > limited using memory.swap.max.
> > 
> > Signed-off-by: Vladimir Davydov <vdavydov@...tuozzo.com>
> 
> setting swap.max=0 will work like mlock ?

For anonymous memory - yes.

Thanks,
Vladimir
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