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

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Date:   Wed, 24 Aug 2022 23:24:43 +0200
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Jan Kara <jack@...e.cz>
Cc:     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 Jan,

Am 24.08.22 um 12:40 schrieb Jan Kara:
> Hi Stefan!
>
> On Wed 24-08-22 12:17:14, Stefan Wahren wrote:
>> Am 23.08.22 um 22:15 schrieb Jan Kara:
>>> Hello,
>>>
>>> So I have implemented mballoc improvements to avoid spreading allocations
>>> even with mb_optimize_scan=1. It fixes the performance regression I was able
>>> to reproduce with reaim on my test machine:
>>>
>>>                        mb_optimize_scan=0     mb_optimize_scan=1     patched
>>> Hmean     disk-1       2076.12 (   0.00%)     2099.37 (   1.12%)     2032.52 (  -2.10%)
>>> Hmean     disk-41     92481.20 (   0.00%)    83787.47 *  -9.40%*    90308.37 (  -2.35%)
>>> Hmean     disk-81    155073.39 (   0.00%)   135527.05 * -12.60%*   154285.71 (  -0.51%)
>>> Hmean     disk-121   185109.64 (   0.00%)   166284.93 * -10.17%*   185298.62 (   0.10%)
>>> Hmean     disk-161   229890.53 (   0.00%)   207563.39 *  -9.71%*   232883.32 *   1.30%*
>>> Hmean     disk-201   223333.33 (   0.00%)   203235.59 *  -9.00%*   221446.93 (  -0.84%)
>>> Hmean     disk-241   235735.25 (   0.00%)   217705.51 *  -7.65%*   239483.27 *   1.59%*
>>> Hmean     disk-281   266772.15 (   0.00%)   241132.72 *  -9.61%*   263108.62 (  -1.37%)
>>> Hmean     disk-321   265435.50 (   0.00%)   245412.84 *  -7.54%*   267277.27 (   0.69%)
>>>
>>> Stefan, can you please test whether these patches fix the problem for you as
>>> well? Comments & review welcome.
>> i tested the whole series against 5.19 and 6.0.0-rc2. In both cases the
>> update process succeed which is a improvement, but the download + unpack
>> duration ( ~ 7 minutes ) is not as good as with mb_optimize_scan=0 ( ~ 1
>> minute ).
> OK, thanks for testing! I'll try to check specifically untar whether I can
> still see some differences in the IO pattern on my test machine.

i made two iostat output logs during the complete download phase with 
5.19 and your series applied. iostat was running via ssh connection and 
rpi-update via serial console.

First with mb_optimize_scan=0

https://github.com/lategoodbye/mb_optimize_scan_regress/blob/main/5.19_SDCIT_patch_nooptimize_download_success.iostat.log

Second with mb_optimize_scan=1

https://github.com/lategoodbye/mb_optimize_scan_regress/blob/main/5.19_SDCIT_patch_optimize_download_success.iostat.log

Maybe this helps

>
>> Unfortuntately i don't have much time this week and next week i'm in
>> holidays.
> No problem.
>
>> Just a question, my tests always had MBCACHE=y . Is it possible that the
>> mb_optimize_scan is counterproductive for MBCACHE in this case?
> MBCACHE (despite similar name) is actually related to extended attributes
> so it likely has no impact on your workload.
>
>> I'm asking because before the download the update script removes the files
>> from the previous update process which already cause a high load.
> Do you mean already the removal step is noticeably slower with
> mb_optimize_scan=1? The removal will be modifying directory blocks, inode
> table blocks, block & inode bitmaps, and group descriptors. So if block
> allocations are more spread (due to mb_optimize_scan=1 used during the
> untar), the removal may also take somewhat longer.
Not sure about this, maybe we should concentrate on download / untar phase.
> 								Honza