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 17:41:51 -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 12/13, Chao Yu wrote:
> On 2022/12/13 6:45, Jaegeuk Kim wrote:
> > 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
> 
> We can set CP_TRIMMED flag only if fitrim was called on full range w/ 4k granularity,
> due to it will check sbi->discard_blks variable to make sure there is no range we
> haven't trimmed.
> 
> > better to get a full discard range after remount even though some are redundant?
> 
> If nodiscard is set, and sbi->discard_blks becomes zero, it says a full range fitrim
> was been triggered.

That gives another assumption, and I prefer to make it simple.

> 
> So, previous check condition has no problem, right?
> 
> 	if ((f2fs_hw_support_discard(sbi) || f2fs_hw_should_discard(sbi)) &&
> 					!sbi->discard_blks && !dropped) {
> 
> Thanks,
> 
> > 
> > > 
> > > Thanks,
> > > 
> > > > 
> > > > Thx,
> > > > Yangtao