linux-kernel - Re: [PATCH 1/2] mm,vmscan: Kill global shrinker lock.

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Date:   Fri, 17 Nov 2017 10:36:49 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Minchan Kim <minchan@...nel.org>,
        Huang Ying <ying.huang@...el.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Thelen <gthelen@...gle.com>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH 1/2] mm,vmscan: Kill global shrinker lock.

On Fri, Nov 17, 2017 at 09:41:46AM -0800, Shakeel Butt wrote:
> On Fri, Nov 17, 2017 at 9:35 AM, Christoph Hellwig <hch@...radead.org> wrote:
> > On Tue, Nov 14, 2017 at 06:37:42AM +0900, Tetsuo Handa wrote:
> >> Since do_shrink_slab() can reschedule, we cannot protect shrinker_list
> >> using one RCU section. But using atomic_inc()/atomic_dec() for each
> >> do_shrink_slab() call will not impact so much.
> >
> > But you could use SRCU..
> 
> I looked into that but was advised to not go through that route due to
> SRCU behind the CONFIG_SRCU. However now I see the precedence of
> "#ifdef CONFIG_SRCU" in drivers/base/core.c and I think if we can take
> that route if even after Minchan's patch the issue persists.

To be honest, I'd rather always require RCU then have core kernel
code reinvent it.