linux-kernel - Re: [PATCH 3/8] mm/vmscan: Throttle reclaim when no progress is being made

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Date:   Wed, 24 Nov 2021 10:53:11 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     "Darrick J. Wong" <djwong@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        NeilBrown <neilb@...e.de>, Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        Dave Chinner <david@...morbit.com>,
        Rik van Riel <riel@...riel.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Linux-MM <linux-mm@...ck.org>,
        Linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/8] mm/vmscan: Throttle reclaim when no progress is
 being made

On Wed, Nov 24, 2021 at 11:43:05AM +0100, Vlastimil Babka wrote:
> >> Any thoughts?  For now I can just hack around this by skipping
> >> reclaim_throttle if cgroup_reclaim() == true, but that's probably not
> >> the correct fix. :)
> >> 
> > 
> > No, it wouldn't be but a possibility is throttling for only 1 jiffy if
> > reclaiming within a memcg and the zone is balanced overall.
> > 
> > The interruptible part should just be the patch below. I need to poke at
> > the cgroup limit part a bit
> 
> As the throttle timeout is short anyway, will the TASK_UNINTERRUPTIBLE vs
> TASK_INTERRUPTIBLE make a difference for the (ability to kill? AFAIU
> typically this inability to kill is because of a loop that doesn't check for
> fatal_signal_pending().
> 

Yep, and the fatal_signal_pending() is lacking within reclaim in general
but I'm undecided on how much that should change in the context of reclaim
throttling but at minimum, I don't want the signal delivery to be masked
or delayed.

-- 
Mel Gorman
SUSE Labs