Re: [PATCH v2] f2fs: get victim segment again after new cp

[Jaegeuk Kim <jaegeuk@kernel.org>]

On Sun, Jul 24, 2016 at 06:38:46AM +0800, Chao Yu wrote:
...

> >> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> >> index de6c41c..ec17096 100644
> >> --- a/fs/f2fs/gc.c
> >> +++ b/fs/f2fs/gc.c
> >> @@ -908,10 +908,14 @@ gc_more:
> >>  		 * enough free sections, we should flush dent/node blocks and do
> >>  		 * garbage collections.
> >>  		 */
> >> -		if (__get_victim(sbi, &segno, gc_type) || prefree_segments(sbi))
> >> +		if (__get_victim(sbi, &segno, gc_type) || prefree_segments(sbi)) {
> >>  			write_checkpoint(sbi, &cpc);
> >> -		else if (has_not_enough_free_secs(sbi, 0))
> > 
> > If segno is NULL_SEGNO, we get a panic when checking the below conditions.
> > Anyway, I don't think we need this condition at all.
> 
> I thinks the condition which trigger our f2fs_bug_on is really a corner case,
> we'd better not waste the victim we found everytime, especially for these
> victims from last background gc's victims.
> 
> What about checking segno first?
> 
> if(segno != NULL_SEGNO && (!get_valid_blocks(sbi, segno, sbi->segs_per_sec) ||
> 	IS_CURSEC(sbi, GET_SECNO(sbi, segno)))
> 	segno = NULL_SEGNO;

My viewpoint is write_checkpoint() flushes node and dentry pages, which provides
another better victims. Another concern is get_valid_blocks and IS_CURSEG are
not covered by any lock.

Thanks,

> 
> Thanks,
> 
> > Let me remove them and just set NULL_SEGNO only after checkpoint.
> > Please check the dev-test repo.
> > 
> > Thanks,
> > 
> >> +			if(!get_valid_blocks(sbi, segno, sbi->segs_per_sec)
> >> +					|| IS_CURSEC(sbi, segno / sbi->segs_per_sec))
> >> +				segno = NULL_SEGNO;
> >> +		} else if (has_not_enough_free_secs(sbi, 0)) {
> >>  			write_checkpoint(sbi, &cpc);
> >> +		}
> >>  	}
> >>  
> >>  	if (segno == NULL_SEGNO && !__get_victim(sbi, &segno, gc_type))
> >> -- 
> >> 1.9.1
> > 
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patterns at an interface-level. Reveals which users, apps, and protocols are 
consuming the most bandwidth. Provides multi-vendor support for NetFlow, 
J-Flow, sFlow and other flows. Make informed decisions using capacity planning
reports.http://sdm.link/zohodev2dev