linux-kernel - Re: Folios give an 80% performance win

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Date:   Sat, 24 Jul 2021 11:09:02 -0700
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Matthew Wilcox <willy@...radead.org>, linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Andres Freund <andres@...razel.de>,
        Michael Larabel <Michael@...haellarabel.com>
Subject: Re: Folios give an 80% performance win

On Sat, 2021-07-24 at 18:27 +0100, Matthew Wilcox wrote:
> What blows me away is the 80% performance improvement for PostgreSQL.
> I know they use the page cache extensively, so it's plausibly real.
> I'm a bit surprised that it has such good locality, and the size of
> the win far exceeds my expectations.  We should probably dive into it
> and figure out exactly what's going on.

Since none of the other tested databases showed more than a 3%
improvement, this looks like an anomalous result specific to something
in postgres ... although the next biggest db: mariadb wasn't part of
the tests so I'm not sure that's definitive.  Perhaps the next step
should be to test mariadb?  Since they're fairly similar in domain
(both full SQL) if mariadb shows this type of improvement, you can
safely assume it's something in the way SQL databases handle paging and
if it doesn't, it's likely fixing a postgres inefficiency.

James