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SubjectRe: [PATCH RFC] f2fs: fix to avoid selecting full segment w/ {AT,}SSR allocator
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Ping,

On 2021/2/20 17:40, 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;
> + }
> + }
> +
> 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
>

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