linux-kernel - Re: [PATCH v2] f2fs: don't call f2fs_issue_discard_timeout() when discard_cmd_cnt is 0 in f2fs_put

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Date:   Mon, 12 Dec 2022 14:45:49 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <chao@...nel.org>
Cc:     Yangtao Li <frank.li@...o.com>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] f2fs: don't call f2fs_issue_discard_timeout() when
 discard_cmd_cnt is 0 in f2fs_put_super()

On 12/12, Chao Yu wrote:
> On 2022/12/12 22:14, Yangtao Li wrote:
> > Hi Chao,
> > 
> > > The difference here is, if we use f2fs_realtime_discard_enable() in
> > > f2fs_put_super(), we will only write checkpoint w/ CP_TRIMMED flag
> > > when discard option is enable and device supports discard.
> > 
> > > But actually, if discard option is disabled, we still needs to give
> > > put_super() a chance to write checkpoint w/ CP_TRIMMED flag.
> > 
> > Why do we still have to set the CP_TRIMMED flag when the discard opt is not set.
> > Did I miss something?
> 
> Hi Yangtao,
> 
> I guess it's up to scenario. e.g.
> 
> mount w/ nodiscard and use FITRIM to trigger in-batch discard,
> if we set CP_TRIMMED flag during umount, next time, after mount
> w/ discard, it doesn't to issue redundant discard.

If fitrim was called with a range, we can get a wrong FI_TRIMMED flag. Isn't it
better to get a full discard range after remount even though some are redundant?

> 
> Thanks,
> 
> > 
> > Thx,
> > Yangtao