Re: [RFC] add ovp valid_blocks check for bg gc victim to fg_gc

[Hou Pengyang <houpengyang@huawei.com>]

On 2017/2/17 7:48, Jaegeuk Kim wrote:
> Hi Pengyang,
>
> Nice
Hi Jaegeuk,
catch!
>
> I think fggc_threshold needs to be revised, and we need to consider about
> general victim selection as well.
>
> Could you take a look at this?
>
>>From 23b265f5ca6405032d092e240c94a827f743e42b Mon Sep 17 00:00:00 2001
> From: Hou Pengyang <houpengyang@huawei.com>
> Date: Thu, 16 Feb 2017 12:34:31 +0000
> Subject: [PATCH] f2fs: add ovp valid_blocks check for bg gc victim to fg_gc
>
> For foreground gc, greedy algorithm should be adapted, which makes
> this formula work well:
>
> 	(2 * (100 / config.overprovision + 1) + 6)
>
> But currently, we fg_gc have a prior to select bg_gc victim segments to gc first,
> these victims are selected by cost-benefit algorithm, we can't guarantee such segments
> have the small valid blocks, which may destroy the f2fs rule, on the worstest case, would
> consume all the free segments.
>
> This patch fix this by add a filter in check_bg_victims, if segment's has # of valid blocks
> over overprovision ratio, skip such segments.
>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Hou Pengyang <houpengyang@huawei.com>
> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> ---
>   fs/f2fs/f2fs.h    |  3 +++
>   fs/f2fs/gc.c      | 22 ++++++++++++++++++++--
>   fs/f2fs/segment.h |  9 +++++++++
>   3 files changed, 32 insertions(+), 2 deletions(-)
>
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index cc22dc458896..1c9f0cc8f027 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -888,6 +888,9 @@ struct f2fs_sb_info {
>   	struct f2fs_gc_kthread	*gc_thread;	/* GC thread */
>   	unsigned int cur_victim_sec;		/* current victim section num */
>
> +	/* threshold for converting bg victims for fg */
> +	u64 fggc_threshold;
> +
>   	/* maximum # of trials to find a victim segment for SSR and GC */
>   	unsigned int max_victim_search;
>
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index 88e5e7b10ab6..fd4e479820e6 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -166,7 +166,8 @@ static void select_policy(struct f2fs_sb_info *sbi, int gc_type,
>   		p->ofs_unit = sbi->segs_per_sec;
>   	}
>
> -	if (p->max_search > sbi->max_victim_search)
> +	/* we need to check every dirty segments in the FG_GC case */
> +	if (gc_type != FG_GC && p->max_search > sbi->max_victim_search)
>   		p->max_search = sbi->max_victim_search;
>
>   	p->offset = sbi->last_victim[p->gc_mode];
> @@ -199,6 +200,10 @@ static unsigned int check_bg_victims(struct f2fs_sb_info *sbi)
>   	for_each_set_bit(secno, dirty_i->victim_secmap, MAIN_SECS(sbi)) {
>   		if (sec_usage_check(sbi, secno))
>   			continue;
> +
> +		if (no_fggc_candidate(sbi, secno))
> +			continue;
> +
>   		clear_bit(secno, dirty_i->victim_secmap);
>   		return secno * sbi->segs_per_sec;
>   	}
> @@ -322,13 +327,15 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
>   			nsearched++;
>   		}
>
> -
>   		secno = GET_SECNO(sbi, segno);
>
>   		if (sec_usage_check(sbi, secno))
>   			goto next;
>   		if (gc_type == BG_GC && test_bit(secno, dirty_i->victim_secmap))
>   			goto next;
> +		if (gc_type == FG_GC && p.alloc_mode == LFS &&
> +					no_fggc_candidate(sbi, secno))
> +			goto next;
>
>   		cost = get_gc_cost(sbi, segno, &p);
>
> @@ -989,5 +996,16 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync, bool background)
>
>   void build_gc_manager(struct f2fs_sb_info *sbi)
>   {
> +	u64 user_block_count, ovp_count, blocks_per_sec, th;
> +
>   	DIRTY_I(sbi)->v_ops = &default_v_ops;
> +
> +	/* threshold of # of valid blocks in a section for victims of FG_GC */
> +	user_block_count = sbi->user_block_count;
> +	ovp_count = SM_I(sbi)->ovp_segments << sbi->log_blocks_per_seg;

About the ovp_count calculation,

in mkfs.f2fs, we get ovp_segment by

     set_cp(overprov_segment_count, (get_sb(segment_count_main) -
            get_cp(rsvd_segment_count)) *
             config.overprovision / 100);

     set_cp(overprov_segment_count, get_cp(overprov_segment_count) +
             get_cp(rsvd_segment_count));

where the overprov calculation is based on the space excluding the
rsvd segment, and the final overprov_segment is sum of the REAL
overprov segments and the rsvd ones.

So, when to calculate the overprov ratio, the rsvd segments should
be subtracted from the ckpt->overprov_semgents?

Thanks,

> +	blocks_per_sec = sbi->blocks_per_seg * sbi->segs_per_sec;
> +
> +	th = user_block_count * 100 * blocks_per_sec /
> +			((user_block_count + ovp_count) * 100);
> +	sbi->fggc_threshold = th;
>   }
> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> index 5cb5755c75d9..f4020f141d83 100644
> --- a/fs/f2fs/segment.h
> +++ b/fs/f2fs/segment.h
> @@ -716,6 +716,15 @@ static inline block_t sum_blk_addr(struct f2fs_sb_info *sbi, int base, int type)
>   				- (base + 1) + type;
>   }
>
> +static inline bool no_fggc_candidate(struct f2fs_sb_info *sbi,
> +						unsigned int secno)
> +{
> +	if (get_valid_blocks(sbi, secno, sbi->segs_per_sec) >=
> +						sbi->fggc_threshold)
> +		return true;
> +	return false;
> +}
> +
>   static inline bool sec_usage_check(struct f2fs_sb_info *sbi, unsigned int secno)
>   {
>   	if (IS_CURSEC(sbi, secno) || (sbi->cur_victim_sec == secno))
>



------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, SlashDot.org! http://sdm.link/slashdot