Messages in this thread Patch in this message | | | Subject | Re: [PATCH 2/5] f2fs: clear the remaining prefree_map of the section | From | Yunlong Song <> | Date | Fri, 13 Jul 2018 11:51:59 +0800 |
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Because in f2fs_clear_prefree_segments, the codes: ... while (1) { int i; start = find_next_bit(prefree_map, MAIN_SEGS(sbi), end + 1); if (start >= MAIN_SEGS(sbi)) break; end = find_next_zero_bit(prefree_map, MAIN_SEGS(sbi), start + 1);
for (i = start; i < end; i++) clear_bit(i, prefree_map); ... next: secno = GET_SEC_FROM_SEG(sbi, start); start_segno = GET_SEG_FROM_SEC(sbi, secno); if (!IS_CURSEC(sbi, secno) && !get_valid_blocks(sbi, start, true)) f2fs_issue_discard(sbi, START_BLOCK(sbi, start_segno), sbi->segs_per_sec << sbi->log_blocks_per_seg);
start = start_segno + sbi->segs_per_sec; if (start < end) goto next; else end = start - 1; ... In round 2, for prefree_map: 1 1 0 1 1, start = 0, end = 2, then
start = start_segno + sbi->segs_per_sec makes start = 5
if (start < end) --> start = 5, end = 2
so end = start -1 --> end = 4, then return to while again, this time skips prefree bit 3 and 4.
On 2018/7/13 11:42, Chao Yu wrote: > On 2018/7/13 11:28, Yunlong Song wrote: >> 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 >> >> round2: rm data block NO.0, NO.1, NO.3, NO.4 >> all invalid, but prefree bit of NO.2 is set and cleared in round1, 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 > Why prefree_map is not 0 0 0 0 0? > > Thanks, > >> valid blocks of this section, so discard issued >> but this time prefree bit of NO.3 and NO.4 is skipped... >> >> round3: >> 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... >> >> On 2018/7/13 11:13, Chao Yu wrote: >>> On 2018/7/12 23:09, Yunlong Song wrote: >>>> For the case when sbi->segs_per_sec > 1, 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, so fix it. >>> I didn't get it, if # 2 segment is not prefree state, so it still has valid >>> blocks there, so we won't issue discard due to below condition, right? >>> >>> if (!IS_CURSEC(sbi, secno) && >>> !get_valid_blocks(sbi, start, true)) >>> >>> Thanks, >>> >>>> Signed-off-by: Yunlong Song <yunlong.song@huawei.com> >>>> --- >>>> fs/f2fs/segment.c | 19 +++++++++++++++++-- >>>> 1 file changed, 17 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c >>>> index 47b6595..fd38b61 100644 >>>> --- a/fs/f2fs/segment.c >>>> +++ b/fs/f2fs/segment.c >>>> @@ -1684,8 +1684,23 @@ void f2fs_clear_prefree_segments(struct f2fs_sb_info *sbi, >>>> start = start_segno + sbi->segs_per_sec; >>>> if (start < end) >>>> goto next; >>>> - else >>>> - end = start - 1; >>>> + else { >>>> + start_segno = start; >>>> + >>>> + while (1) { >>>> + start = find_next_bit(prefree_map, start_segno, >>>> + end + 1); >>>> + if (start >= start_segno) >>>> + break; >>>> + end = find_next_zero_bit(prefree_map, start_segno, >>>> + start + 1); >>>> + for (i = start; i < end; i++) >>>> + clear_bit(i, prefree_map); >>>> + dirty_i->nr_dirty[PRE] -= end - start; >>>> + } >>>> + >>>> + end = start_segno - 1; >>>> + } >>>> } >>>> mutex_unlock(&dirty_i->seglist_lock); >>>> >>>> >>> . >>> > > . >
-- Thanks, Yunlong Song
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