[PATCH v2] f2fs: fix to correct freed section number during gc

[PATCH v2] f2fs: fix to correct freed section number during gc

[Chao Yu]

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@samsung.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++;
+	}
+
+	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

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

[Jaegeuk Kim]

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@samsung.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

RE: [PATCH v2] f2fs: fix to correct freed section number during gc

[Chao Yu]

> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk@kernel.org]
> Sent: Saturday, September 26, 2015 2:04 AM
> To: Chao Yu
> Cc: linux-f2fs-devel@lists.sourceforge.net; linux-kernel@vger.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@samsung.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++;

I'll update it. See the following v3 patch.

Thanks,

> 
> > +
> > +	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