linux-kernel - Re: [PATCH v2] f2fs: fix to correct freed section number during gc

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Date:	Fri, 25 Sep 2015 11:04:17 -0700
From:	Jaegeuk Kim <jaegeuk@...nel.org>
To:	Chao Yu <chao2.yu@...sung.com>
Cc:	linux-f2fs-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] f2fs: fix to correct freed section number during gc

On Fri, Sep 25, 2015 at 05:50:55PM +0800, Chao Yu wrote:
> This patch fixes to maintain the right section count freed in garbage
> collecting when triggering a foreground gc.
> 
> Besides, when a foreground gc is running on current selected section, once
> we fail to gc one segment, it's better to abandon gcing the left segments
> in current section, because anyway we will select next victim for
> foreground gc, so gc on the left segments in previous section will become
> overhead and also cause the long latency for caller.
> 
> Signed-off-by: Chao Yu <chao2.yu@...sung.com>
> ---
> v2:
>  o avoid calc the wrong value when freed segments across sections.
>  fs/f2fs/gc.c | 22 +++++++++++++++++-----
>  1 file changed, 17 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index e932740..256ebd4 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -802,7 +802,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi)
>  	unsigned int segno = NULL_SEGNO;
>  	unsigned int i;
>  	int gc_type = BG_GC;
> -	int nfree = 0;
> +	int sec_freed = 0, seg_freed;
>  	int ret = -1;
>  	struct cp_control cpc;
>  	struct gc_inode_list gc_list = {
> @@ -817,7 +817,7 @@ gc_more:
>  	if (unlikely(f2fs_cp_error(sbi)))
>  		goto stop;
>  
> -	if (gc_type == BG_GC && has_not_enough_free_secs(sbi, nfree)) {
> +	if (gc_type == BG_GC && has_not_enough_free_secs(sbi, sec_freed)) {
>  		gc_type = FG_GC;
>  		if (__get_victim(sbi, &segno, gc_type) || prefree_segments(sbi))
>  			write_checkpoint(sbi, &cpc);
> @@ -833,13 +833,25 @@ gc_more:
>  		ra_meta_pages(sbi, GET_SUM_BLOCK(sbi, segno), sbi->segs_per_sec,
>  								META_SSA);
>  
> -	for (i = 0; i < sbi->segs_per_sec; i++)
> -		nfree += do_garbage_collect(sbi, segno + i, &gc_list, gc_type);
> +	for (i = 0, seg_freed = 0; i < sbi->segs_per_sec; i++) {
> +		/*
> +		 * for FG_GC case, halt gcing left segments once failed one
> +		 * of segments in selected section to avoid long latency.
> +		 */
> +		if (!do_garbage_collect(sbi, segno + i, &gc_list, gc_type) &&
> +				gc_type == FG_GC)
> +			break;
> +		if (gc_type == FG_GC)
> +			seg_freed++;
> +	}

How about?

	if (i == sbi->segs_per_sec && gc_type == FG_GC)
		sec_free++;

> +
> +	if (seg_freed == sbi->segs_per_sec)
> +		sec_freed++;
>  
>  	if (gc_type == FG_GC)
>  		sbi->cur_victim_sec = NULL_SEGNO;
>  
> -	if (has_not_enough_free_secs(sbi, nfree))
> +	if (has_not_enough_free_secs(sbi, sec_freed))
>  		goto gc_more;
>  
>  	if (gc_type == FG_GC)
> -- 
> 2.5.2
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