Messages in this thread | | | Subject | Re: [PATCH v3] f2fs: issue discard align to section in LFS mode | From | Chao Yu <> | Date | Tue, 24 Jul 2018 10:40:27 +0800 |
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On 2018/7/19 20:58, Yunlong Song wrote: > For the case when sbi->segs_per_sec > 1 with lfs mode, take > section:segment = 5 for example, if the section prefree_map is > ...previous section | current section (1 1 0 1 1) | next section..., > then the start = x, end = x + 1, after start = start_segno + > sbi->segs_per_sec, start = x + 5, then it will skip x + 3 and x + 4, but > their bitmap is still set, which will cause duplicated > f2fs_issue_discard of this same section in the next write_checkpoint: > > round 1: section bitmap : 1 1 1 1 1, all valid, prefree_map: 0 0 0 0 0 > then rm data block NO.2, block NO.2 becomes invalid, prefree_map: 0 0 1 0 0 > write_checkpoint: section bitmap: 1 1 0 1 1, prefree_map: 0 0 0 0 0, > prefree of NO.2 is cleared, and no discard issued > > round 2: rm data block NO.0, NO.1, NO.3, NO.4 > all invalid, but prefree bit of NO.2 is set and cleared in round 1, then > prefree_map: 1 1 0 1 1 > write_checkpoint: section bitmap: 0 0 0 0 0, prefree_map: 0 0 0 1 1, no > valid blocks of this section, so discard issued, but this time prefree > bit of NO.3 and NO.4 is skipped due to start = start_segno + sbi->segs_per_sec; > > round 3: > write_checkpoint: section bitmap: 0 0 0 0 0, prefree_map: 0 0 0 1 1 -> > 0 0 0 0 0, no valid blocks of this section, so discard issued, > this time prefree bit of NO.3 and NO.4 is cleared, but the discard of > this section is sent again... > > To fix this problem, we can align the start and end value to section > boundary for fstrim and real-time discard operation, and decide to issue > discard only when the whole section is invalid, which can issue discard > aligned to section size as much as possible and avoid redundant discard. > > Signed-off-by: Yunlong Song <yunlong.song@huawei.com> > Signed-off-by: Chao Yu <yuchao0@huawei.com> Reviewed-by: Chao Yu <yuchao0@huawei.com>
Thanks,
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