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Date:   Thu, 18 Mar 2021 10:17:40 -0700
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     Chao Yu <yuchao0@huawei.com>
Cc:     linux-f2fs-devel@lists.sourceforge.net,
        linux-kernel@vger.kernel.org, chao@kernel.org
Subject: Re: [PATCH RFC] f2fs: fix to avoid selecting full segment w/
 {AT,}SSR allocator
Message-ID: <YFOLNGo+/8sKQ7si@google.com>
References: <20210220094052.64905-1-yuchao0@huawei.com>
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On 02/20, Chao Yu wrote:
> In cp disabling mode, there could be a condition
> - target segment has 128 ckpt valid blocks
> - GC migrates 128 valid blocks to other segment (segment is still in
> dirty list)
> - GC migrates 384 blocks to target segment (segment has 128 cp_vblocks
> and 384 vblocks)
> - If GC selects target segment via {AT,}SSR allocator, however there is
> no free space in targe segment.
> 
> Fixes: 4354994f097d ("f2fs: checkpoint disabling")
> Fixes: 093749e296e2 ("f2fs: support age threshold based garbage collection")
> Signed-off-by: Chao Yu <yuchao0@huawei.com>
> ---
>  fs/f2fs/f2fs.h    |  1 +
>  fs/f2fs/gc.c      | 17 +++++++++++++----
>  fs/f2fs/segment.c | 20 ++++++++++++++++++++
>  3 files changed, 34 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index ed7807103c8e..9c753eff0814 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -3376,6 +3376,7 @@ block_t f2fs_get_unusable_blocks(struct f2fs_sb_info *sbi);
>  int f2fs_disable_cp_again(struct f2fs_sb_info *sbi, block_t unusable);
>  void f2fs_release_discard_addrs(struct f2fs_sb_info *sbi);
>  int f2fs_npages_for_summary_flush(struct f2fs_sb_info *sbi, bool for_ra);
> +bool segment_has_free_slot(struct f2fs_sb_info *sbi, int segno);
>  void f2fs_init_inmem_curseg(struct f2fs_sb_info *sbi);
>  void f2fs_save_inmem_curseg(struct f2fs_sb_info *sbi);
>  void f2fs_restore_inmem_curseg(struct f2fs_sb_info *sbi);
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index 86ba8ed0b8a7..a1d8062cdace 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -392,10 +392,6 @@ static void add_victim_entry(struct f2fs_sb_info *sbi,
>  		if (p->gc_mode == GC_AT &&
>  			get_valid_blocks(sbi, segno, true) == 0)
>  			return;
> -
> -		if (p->alloc_mode == AT_SSR &&
> -			get_seg_entry(sbi, segno)->ckpt_valid_blocks == 0)
> -			return;
>  	}
>  
>  	for (i = 0; i < sbi->segs_per_sec; i++)
> @@ -736,6 +732,19 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
>  		if (gc_type == BG_GC && test_bit(secno, dirty_i->victim_secmap))
>  			goto next;
>  
> +		if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED))) {
> +			/*
> +			 * to avoid selecting candidate which has below valid
> +			 * block distribution:
> +			 * partial blocks are valid and all left ones are valid
> +			 * in previous checkpoint.
> +			 */
> +			if (p.alloc_mode == SSR || p.alloc_mode == AT_SSR) {
> +				if (!segment_has_free_slot(sbi, segno))
> +					goto next;

Do we need to change this to check free_slot instead of get_ckpt_valid_blocks()?

 732                 if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED) &&
 733                                         get_ckpt_valid_blocks(sbi, segno) &&
 734                                         p.alloc_mode == LFS))


> +			}
> +		}
> +
>  		if (is_atgc) {
>  			add_victim_entry(sbi, &p, segno);
>  			goto next;
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 2d5a82c4ca15..deaf57e13125 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -2650,6 +2650,26 @@ static void __refresh_next_blkoff(struct f2fs_sb_info *sbi,
>  		seg->next_blkoff++;
>  }
>  
> +bool segment_has_free_slot(struct f2fs_sb_info *sbi, int segno)
> +{
> +	struct sit_info *sit = SIT_I(sbi);
> +	struct seg_entry *se = get_seg_entry(sbi, segno);
> +	int entries = SIT_VBLOCK_MAP_SIZE / sizeof(unsigned long);
> +	unsigned long *target_map = SIT_I(sbi)->tmp_map;
> +	unsigned long *ckpt_map = (unsigned long *)se->ckpt_valid_map;
> +	unsigned long *cur_map = (unsigned long *)se->cur_valid_map;
> +	int i, pos;
> +
> +	down_write(&sit->sentry_lock);
> +	for (i = 0; i < entries; i++)
> +		target_map[i] = ckpt_map[i] | cur_map[i];
> +
> +	pos = __find_rev_next_zero_bit(target_map, sbi->blocks_per_seg, 0);
> +	up_write(&sit->sentry_lock);
> +
> +	return pos < sbi->blocks_per_seg;
> +}
> +
>  /*
>   * This function always allocates a used segment(from dirty seglist) by SSR
>   * manner, so it should recover the existing segment information of valid blocks
> -- 
> 2.29.2