linux-ext4 - Re: [PATCH v2] ext4: improve discard efficiency

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Date:   Mon, 24 Jul 2023 11:16:20 +0800
From:   Guoqing Jiang <guoqing.jiang@...ux.dev>
To:     Fengnan Chang <changfengnan@...edance.com>,
        adilger.kernel@...ger.ca, tytso@....edu
Cc:     linux-ext4@...r.kernel.org,
        kernel test robot <oliver.sang@...el.com>
Subject: Re: [PATCH v2] ext4: improve discard efficiency

Hi,

On 7/19/23 17:36, Fengnan Chang wrote:
> In commit a015434480dc("ext4: send parallel discards on commit
> completions"), issue all discard commands in parallel make all
> bios could merged into one request, so lowlevel drive can issue
> multi segments in one time which is more efficiency, but commit
> 55cdd0af2bc5 ("ext4: get discard out of jbd2 commit kthread contex")
> seems broke this way, let's fix it.
> In my test, the time of fstrim fs with multi big sparse file
> reduce from 6.7s to 1.3s.

I tried with a 20T sparse file with latest kernel (6.5-rc2+ commit 
f7e3a1baf).

truncate -s 20T sparse1.img
mkfs.ext4 sparse1.img
mount -o discard sparse1.img /mnt/
time fstrim /mnt

1. without the patch

[root@...alhost ~]# time fstrim /mnt

real    0m13.496s
user    0m0.002s
sys     0m5.202s

2. with the patch

[root@...alhost ~]# time fstrim /mnt

real    0m15.956s
user    0m0.000s
sys     0m7.251s

The result is different from your side, could you share your test?

Thanks,
Guoqing