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.s...@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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