linux-ext4 - Re: [PATCH 0/2] ext4: Fix performance regression with mballoc

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Message-ID: <20220826101522.b552tn646qobrjdx@quack3>
Date:   Fri, 26 Aug 2022 12:15:22 +0200
From:   Jan Kara <jack@...e.cz>
To:     Stefan Wahren <stefan.wahren@...e.com>
Cc:     Jan Kara <jack@...e.cz>, Ted Tso <tytso@....edu>,
        linux-ext4@...r.kernel.org,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        Ojaswin Mujoo <ojaswin@...ux.ibm.com>,
        Harshad Shirwadkar <harshadshirwadkar@...il.com>
Subject: Re: [PATCH 0/2] ext4: Fix performance regression with mballoc

Hi Stefan,

On Thu 25-08-22 18:57:08, Stefan Wahren wrote:
> > Perhaps if you just download the archive manually, call sync(1), and measure
> > how long it takes to (untar the archive + sync) in mb_optimize_scan=0/1 we
> > can see whether plain untar is indeed making the difference or there's
> > something else influencing the result as well (I have checked and
> > rpi-update does a lot of other deleting & copying as the part of the
> > update)? Thanks.
> 
> mb_optimize_scan=0 -> almost 5 minutes
> 
> mb_optimize_scan=1 -> almost 18 minutes
> 
> https://github.com/lategoodbye/mb_optimize_scan_regress/commit/3f3fe8f87881687bb654051942923a6b78f16dec

Thanks! So now the iostat data indeed looks substantially different.

			nooptimize	optimize
Total written		183.6 MB	190.5 MB
Time (recorded)		283 s		1040 s
Avg write request size	79 KB		41 KB

So indeed with mb_optimize_scan=1 we do submit substantially smaller
requests on average. So far I'm not sure why that is. Since Ojaswin can
reproduce as well, let's see what he can see from block location info.
Thanks again for help with debugging this and enjoy your vacation!

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR