linux-kernel - Re: [RFC PATCH] mm/workingset : judge file page activity via timestamp

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Date:   Wed, 17 Apr 2019 06:37:25 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Zhaoyang Huang <huangzhaoyang@...il.com>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        David Rientjes <rientjes@...gle.com>,
        Zhaoyang Huang <zhaoyang.huang@...soc.com>,
        Roman Gushchin <guro@...com>, Jeff Layton <jlayton@...hat.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [RFC PATCH] mm/workingset : judge file page activity via
 timestamp

On Wed, Apr 17, 2019 at 08:26:22PM +0800, Zhaoyang Huang wrote:
[quoting Johannes here]
> As Matthew says, you are fairly randomly making refault activations
> more aggressive (especially with that timestamp unpacking bug), and
> while that expectedly boosts workload transition / startup, it comes
> at the cost of disrupting stable states because you can flood a very
> active in-ram workingset with completely cold cache pages simply
> because they refault uniformly wrt each other.
> [HZY]: I analysis the log got from trace_printk, what we activate have
> proven record of long refault distance but very short refault time.

You haven't addressed my point, which is that you were only testing
workloads for which your changed algorithm would improve the results.
What you haven't done is shown how other workloads would be negatively
affected.

Once you do that, we can make a decision about whether to improve your
workload by X% and penalise that other workload by Y%.