linux-kernel - Re: [PATCH] zswap: Same-filled pages handling

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Date:   Tue, 28 Nov 2017 06:35:10 -0500
From:   Dan Streetman <ddstreet@...e.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Srividya Desireddy <srividya.dr@...sung.com>,
        "sjenning@...hat.com" <sjenning@...hat.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "penberg@...nel.org" <penberg@...nel.org>,
        Dinakar Reddy Pathireddy <dinakar.p@...sung.com>,
        SHARAN ALLUR <sharan.allur@...sung.com>,
        RAJIB BASU <rajib.basu@...sung.com>,
        JUHUN KIM <juhunkim@...sung.com>,
        "srividya.desireddy@...il.com" <srividya.desireddy@...il.com>
Subject: Re: [PATCH] zswap: Same-filled pages handling

On Mon, Nov 20, 2017 at 6:46 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
>
> On Wed, 18 Oct 2017 10:48:32 +0000 Srividya Desireddy <srividya.dr@...sung.com> wrote:
>
> > +/* Enable/disable handling same-value filled pages (enabled by default) */
> > +static bool zswap_same_filled_pages_enabled = true;
> > +module_param_named(same_filled_pages_enabled, zswap_same_filled_pages_enabled,
> > +                bool, 0644);
>
> Do we actually need this?  Being able to disable the new feature shows
> a certain lack of confidence ;) I guess we can remove it later as that
> confidence grows.

No, it's not absolutely needed to have the param to enable/disable the
feature, but my concern is around how many pages actually benefit from
this, since it adds some overhead to check every page - the usefulness
of the feature depends entirely on the system workload.  So having a
way to disable it is helpful, for use cases that know it won't benefit
them.

>
> Please send a patch to document this parameter in
> Documentation/vm/zswap.txt.  And if you have time, please check that
> the rest of that file is up-to-date?

Srividya, can you send a patch to doc this feature please.

I'll check the rest of the file is correct.

>
> Thanks.
>