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From: Michal Hocko <mhocko@kernel.org>
To: David Rientjes <rientjes@google.com>
Cc: Minchan Kim <minchan@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [patch] mm, vmscan: avoid thrashing anon lru when free + file is low
Date: Wed, 19 Apr 2017 09:04:25 +0200	[thread overview]
Message-ID: <20170419070424.GA28263@dhcp22.suse.cz> (raw)
In-Reply-To: <alpine.DEB.2.10.1704181402510.112481@chino.kir.corp.google.com>

On Tue 18-04-17 14:32:56, David Rientjes wrote:
[...]
> If the suggestion is checking
> NR_ACTIVE_ANON + NR_INACTIVE_ANON > total_high_wmark pages, it would be a 
> separate heurstic to address a problem that I'm not having :)  My issue is 
> specifically when NR_ACTIVE_FILE + NR_INACTIVE_FILE < total_high_wmark, 
> NR_ACTIVE_ANON + NR_INACTIVE_ANON is very large, but all not on this 
> lruvec's evictable lrus.

Hmm, why are those pages not moved to the unevictable LRU lists?

> This is the reason why I chose lruvec_lru_size() rather than per-node 
> statistics.  The argument could also be made for the file lrus in the 
> get_scan_count() heuristic that forces SCAN_ANON, but I have not met such 
> an issue (yet).  I could follow-up with that change or incorporate it into 
> a v2 of this patch if you'd prefer.
> 
> In other words, I want get_scan_count() to not force SCAN_ANON and 
> fallback to SCAN_FRACT, absent other heuristics, if the amount of 
> evictable anon is below a certain threshold for this lruvec.  I 
> arbitrarily chose SWAP_CLUSTER_MAX to be conservative, but I could easily 
> compare to total_high_wmark as well, although I would consider that more 
> aggressive.
> 
> So we're in global reclaim, our file lrus are below thresholds, but we 
> don't want to force SCAN_ANON for all lruvecs if there's not enough to 
> reclaim from evictable anon.  Do you have a suggestion for how to 
> implement this logic other than this patch?

I agree that forcing SCAN_ANON without looking at the ANON lru size is
not optimal but I would rather see the same criterion for both anon and
file. get_scan_count is full of magic heuristics which tend to break for
different workloads. Let's not add another magic on top please.
-- 
Michal Hocko
SUSE Labs

  parent reply	other threads:[~2017-04-19  7:04 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-18  0:06 David Rientjes
2017-04-18  1:36 ` Minchan Kim
2017-04-18 21:32   ` David Rientjes
2017-04-19  0:14     ` Minchan Kim
2017-04-19 23:24       ` David Rientjes
2017-04-20  6:09         ` Minchan Kim
2017-05-01 21:34           ` [patch v2] " David Rientjes
2017-05-02  8:02             ` Michal Hocko
2017-05-02 20:41               ` David Rientjes
2017-05-03  6:15                 ` Michal Hocko
2017-05-03  7:06                   ` Michal Hocko
2017-05-03  8:49                     ` Michal Hocko
2017-05-03 22:52                       ` David Rientjes
2017-05-04 11:43                         ` Michal Hocko
2017-05-31 15:20             ` Michal Hocko
2017-06-02 20:36             ` Andrew Morton
2017-06-04 22:27               ` David Rientjes
2017-04-19  7:04     ` Michal Hocko [this message]
2017-04-18  7:11 ` [patch] " Michal Hocko

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