linux-kernel - Re: [f2fs-dev] [PATCH 08/10] f2fs: relax async discard commands more

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Date:   Thu, 5 Jan 2017 11:46:04 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 08/10] f2fs: relax async discard commands more

On 01/05, Chao Yu wrote:
> On 2017/1/4 17:29, Chao Yu wrote:
> > On 2016/12/31 2:51, Jaegeuk Kim wrote:
> >> This patch relaxes async discard commands to avoid waiting its end_io during
> >> checkpoint.
> >> Instead of waiting them during checkpoint, it will be done when actually reusing
> >> them.
> >>
> >> Test on initial partition of nvme drive.
> >>
> >>  # time fstrim /mnt/test
> >>
> >> Before : 6.158s
> >> After : 4.822s
> >>
> >> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> > 
> > Reviewed-by: Chao Yu <yuchao0@...wei.com>
> > 
> > One comment below,
> 
> I still have a comment on this patch.
> 
> >> -void f2fs_wait_all_discard_bio(struct f2fs_sb_info *sbi)
> >> +/* This should be covered by global mutex, &sit_i->sentry_lock */
> >> +void f2fs_wait_discard_bio(struct f2fs_sb_info *sbi, unsigned int segno)
> >>  {
> >>  	struct list_head *wait_list = &(SM_I(sbi)->wait_list);
> >>  	struct bio_entry *be, *tmp;
> >> @@ -646,7 +650,15 @@ void f2fs_wait_all_discard_bio(struct f2fs_sb_info *sbi)
> >>  		struct bio *bio = be->bio;
> >>  		int err;
> >>  
> >> -		wait_for_completion_io(&be->event);
> >> +		if (!completion_done(&be->event)) {
> >> +			if ((be->start_segno >= segno &&
> >> +					be->end_segno <= segno) ||
> > 
> > segno >= be->start_segno && segno < be->end_segno ?
> 
> Can you check this?

The be->start_segno and be->end_segno are assigned by:

unsigned int start_segno = GET_SEGNO(sbi, blkstart);
unsigned int end_segno = GET_SEGNO(sbi, blkstart + blklen);

in __f2fs_issue_discard_async().

So, the problem comes when, for example, blkstart = 0 and blklen = 512.

I should have got the end_segno by:

unsigned int end_segno = GET_SEGNO(sbi, blkstart + blklen - 1);

Thanks,