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From: Michal Hocko <mhocko@kernel.org>
To: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Minchan Kim <minchan@kernel.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [patch v2] mm, vmscan: avoid thrashing anon lru when free + file is low
Date: Tue, 2 May 2017 10:02:47 +0200	[thread overview]
Message-ID: <20170502080246.GD14593@dhcp22.suse.cz> (raw)
In-Reply-To: <alpine.DEB.2.10.1705011432220.137835@chino.kir.corp.google.com>

On Mon 01-05-17 14:34:21, David Rientjes wrote:
[...]
> @@ -2204,8 +2204,17 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
>  		}
>  
>  		if (unlikely(pgdatfile + pgdatfree <= total_high_wmark)) {
> -			scan_balance = SCAN_ANON;
> -			goto out;
> +			/*
> +			 * Force SCAN_ANON if there are enough inactive
> +			 * anonymous pages on the LRU in eligible zones.
> +			 * Otherwise, the small LRU gets thrashed.
> +			 */
> +			if (!inactive_list_is_low(lruvec, false, sc, false) &&
> +			    lruvec_lru_size(lruvec, LRU_INACTIVE_ANON, sc->reclaim_idx)
> +					>> sc->priority) {
> +				scan_balance = SCAN_ANON;
> +				goto out;
> +			}

I have already asked and my questions were ignored. So let me ask again
and hopefuly not get ignored this time. So Why do we need a different
criterion on anon pages than file pages? I do agree that blindly
scanning anon pages when file pages are low is very suboptimal but this
adds yet another heuristic without _any_ numbers. Why cannot we simply
treat anon and file pages equally? Something like the following

	if (pgdatfile + pgdatanon + pgdatfree > 2*total_high_wmark) {
		scan_balance = SCAN_FILE;
		if (pgdatfile < pgdatanon)
			scan_balance = SCAN_ANON;
		goto out;
	}

Also it would help to describe the workload which can trigger this
behavior so that we can compare numbers before and after this patch.
-- 
Michal Hocko
SUSE Labs

  reply	other threads:[~2017-05-02  8:03 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-18  0:06 [patch] " 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 [this message]
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     ` [patch] " Michal Hocko
2017-04-18  7:11 ` Michal Hocko

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