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Date:   Fri, 22 Jan 2021 08:55:31 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Daeho Jeong <daeho43@...il.com>, <linux-kernel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>, <kernel-team@...roid.com>
CC:     Sungjong Seo <sj1557.seo@...sung.com>,
        Daeho Jeong <daehojeong@...gle.com>
Subject: Re: [f2fs-dev] [PATCH v5 1/2] f2fs: introduce checkpoint=merge mount
 option

If there is no update in v5, it will be better to include my Reviewed-by
tag, please note that. :)

Thanks,

On 2021/1/21 21:45, Daeho Jeong wrote:
> From: Daeho Jeong<daehojeong@...gle.com>
> 
> We've added a new mount option "checkpoint=merge", which creates a
> kernel daemon and makes it to merge concurrent checkpoint requests as
> much as possible to eliminate redundant checkpoint issues. Plus, we
> can eliminate the sluggish issue caused by slow checkpoint operation
> when the checkpoint is done in a process context in a cgroup having
> low i/o budget and cpu shares. To make this do better, we set the
> default i/o priority of the kernel daemon to "3", to give one higher
> priority than other kernel threads. The below verification result
> explains this.
> The basic idea has come fromhttps://opensource.samsung.com.
> 
> [Verification]
> Android Pixel Device(ARM64, 7GB RAM, 256GB UFS)
> Create two I/O cgroups (fg w/ weight 100, bg w/ wight 20)
> Set "strict_guarantees" to "1" in BFQ tunables
> 
> In "fg" cgroup,
> - thread A => trigger 1000 checkpoint operations
>    "for i in `seq 1 1000`; do touch test_dir1/file; fsync test_dir1;
>     done"
> - thread B => gererating async. I/O
>    "fio --rw=write --numjobs=1 --bs=128k --runtime=3600 --time_based=1
>         --filename=test_img --name=test"
> 
> In "bg" cgroup,
> - thread C => trigger repeated checkpoint operations
>    "echo $$ > /dev/blkio/bg/tasks; while true; do touch test_dir2/file;
>     fsync test_dir2; done"
> 
> We've measured thread A's execution time.
> 
> [ w/o patch ]
> Elapsed Time: Avg. 68 seconds
> [ w/  patch ]
> Elapsed Time: Avg. 48 seconds
> 
> Signed-off-by: Daeho Jeong<daehojeong@...gle.com>
> Signed-off-by: Sungjong Seo<sj1557.seo@...sung.com>

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