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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20211014130312.GA3959@techsingularity.net>
Date:   Thu, 14 Oct 2021 14:03:12 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Linux-MM <linux-mm@...ck.org>, NeilBrown <neilb@...e.de>,
        Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        "Darrick J . Wong" <djwong@...nel.org>,
        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-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 Thu, Oct 14, 2021 at 02:31:17PM +0200, Vlastimil Babka wrote:
> On 10/8/21 15:53, Mel Gorman wrote:
> > Memcg reclaim throttles on congestion if no reclaim progress is made.
> > This makes little sense, it might be due to writeback or a host of
> > other factors.
> > 
> > For !memcg reclaim, it's messy. Direct reclaim primarily is throttled
> > in the page allocator if it is failing to make progress. Kswapd
> > throttles if too many pages are under writeback and marked for
> > immediate reclaim.
> > 
> > This patch explicitly throttles if reclaim is failing to make progress.
> > 
> > Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
> ...
> > @@ -3769,6 +3797,16 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
> >  	trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
> >  	set_task_reclaim_state(current, NULL);
> >  
> > +	if (!nr_reclaimed) {
> > +		struct zoneref *z;
> > +		pg_data_t *pgdat;
> > +
> > +		z = first_zones_zonelist(zonelist, sc.reclaim_idx, sc.nodemask);
> > +		pgdat = zonelist_zone(z)->zone_pgdat;
> > +
> > +		reclaim_throttle(pgdat, VMSCAN_THROTTLE_NOPROGRESS, HZ/10);
> > +	}
> 
> Is this necessary? AFAICS here we just returned from:
> 
> do_try_to_free_pages()
>   shrink_zones()
>    for_each_zone()...
>      consider_reclaim_throttle()
> 
> Which already throttles when needed and using the appropriate pgdat, while
> here we have to somewhat awkwardly assume the preferred one.
> 

Yes, you're right, consider_reclaim_throttle not only throttles on the
appropriate pgdat but takes priority into account.

Well spotted!

-- 
Mel Gorman
SUSE Labs