linux-kernel - Re: [PATCH v6] zswap: memcontrol: implement zswap writeback disabling

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Date:   Fri, 8 Dec 2023 11:58:21 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Nhat Pham <nphamcs@...il.com>
Cc:     tj@...nel.org, lizefan.x@...edance.com, hannes@...xchg.org,
        cerasuolodomenico@...il.com, yosryahmed@...gle.com,
        sjenning@...hat.com, ddstreet@...e.org, vitaly.wool@...sulko.com,
        mhocko@...nel.org, roman.gushchin@...ux.dev, shakeelb@...gle.com,
        muchun.song@...ux.dev, hughd@...gle.com, corbet@....net,
        konrad.wilk@...cle.com, senozhatsky@...omium.org, rppt@...nel.org,
        linux-mm@...ck.org, kernel-team@...a.com,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        david@...t.cz, chrisl@...nel.org
Subject: Re: [PATCH v6] zswap: memcontrol: implement zswap writeback
 disabling

On Thu, 7 Dec 2023 17:14:22 -0800 Nhat Pham <nphamcs@...il.com> wrote:

> > I don't have any concrete numbers though - any numbers I can pull out
> > are from highly artificial tasks that only serve to test the
> > correctness aspect of the implementation. zswap.writeback disablement
> > would of course be faster in these situations (up to 33%!!!!) - but
> > that's basically just saying HDD is slow. Which is not very
> > informative or surprising, so I did not include it in the changelog.
> 
> For instance, on a server with HDD, I allocate memories and populate
> them with random values (so that zswap store will always fail), and
> specify memory.high low enough to trigger reclaim. The time it takes
> to allocate the memories and just read through it a couple of times
> (doing silly things like computing the values' average etc.):
> 
> zswap.writeback disabled:
> real 0m30.537s
> user 0m23.687s
> sys 0m6.637s
> 0 pages swapped in
> 0 pages swapped out
> 
> zswap.writeback enabled:
> real 0m45.061s
> user 0m24.310s
> sys 0m8.892s
> 712686 pages swapped in
> 461093 pages swapped out
> 
> (the last two lines are from vmstat -s).

I pasted that also.