| Message ID | 20250109122755.177926-1-guochunhai@vivo.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [f2fs-dev,v2] f2fs: fix missing discard for active segments | expand |
On 1/9/25 20:27, Chunhai Guo wrote: > During a checkpoint, the current active segment X may not be handled > properly. This occurs when segment X has 0 valid blocks and a non-zero How does this happen? Allocator selects a dirty segment w/ SSR? and the left valid data blocks were deleted later before following checkpoint? If so, pending discard count in that segment should be in range of (0, 512)? Thanks, > number of discard blocks, for the following reasons: > > locate_dirty_segment() does not mark any active segment as a prefree > segment. As a result, segment X is not included in dirty_segmap[PRE], and > f2fs_clear_prefree_segments() skips it when handling prefree segments. > > add_discard_addrs() skips any segment with 0 valid blocks, so segment X is > also skipped. > > Consequently, no `struct discard_cmd` is actually created for segment X. > However, the ckpt_valid_map and cur_valid_map of segment X are synced by > seg_info_to_raw_sit() during the current checkpoint process. As a result, > it cannot find the missing discard bits even in subsequent checkpoints. > Consequently, the value of sbi->discard_blks remains non-zero. Thus, when > f2fs is umounted, CP_TRIMMED_FLAG will not be set due to the non-zero > sbi->discard_blks. > > Relevant code process: > > f2fs_write_checkpoint() > f2fs_flush_sit_entries() > list_for_each_entry_safe(ses, tmp, head, set_list) { > for_each_set_bit_from(segno, bitmap, end) { > ... > add_discard_addrs(sbi, cpc, false); // skip segment X due to its 0 valid blocks > ... > seg_info_to_raw_sit(); // sync ckpt_valid_map with cur_valid_map for segment X > ... > } > } > f2fs_clear_prefree_segments(); // segment X is not included in dirty_segmap[PRE] and is skipped > > Since add_discard_addrs() can handle active segments with non-zero valid > blocks, it is reasonable to fix this issue by allowing it to also handle > active segments with 0 valid blocks. > > Fixes: b29555505d81 ("f2fs: add key functions for small discards") > Signed-off-by: Chunhai Guo <guochunhai@vivo.com> > --- > v1: https://lore.kernel.org/linux-f2fs-devel/20241203065108.2763436-1-guochunhai@vivo.com/ > v1->v2: > - Modify the commit message to make it easier to understand. > - Add fixes to the commit. > --- > fs/f2fs/segment.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c > index 86e547f008f9..13ee73a3c481 100644 > --- a/fs/f2fs/segment.c > +++ b/fs/f2fs/segment.c > @@ -2090,7 +2090,9 @@ static bool add_discard_addrs(struct f2fs_sb_info *sbi, struct cp_control *cpc, > return false; > > if (!force) { > - if (!f2fs_realtime_discard_enable(sbi) || !se->valid_blocks || > + if (!f2fs_realtime_discard_enable(sbi) || > + (!se->valid_blocks && > + !IS_CURSEG(sbi, cpc->trim_start)) || > SM_I(sbi)->dcc_info->nr_discards >= > SM_I(sbi)->dcc_info->max_discards) > return false;
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c index 86e547f008f9..13ee73a3c481 100644 --- a/fs/f2fs/segment.c +++ b/fs/f2fs/segment.c @@ -2090,7 +2090,9 @@ static bool add_discard_addrs(struct f2fs_sb_info *sbi, struct cp_control *cpc, return false; if (!force) { - if (!f2fs_realtime_discard_enable(sbi) || !se->valid_blocks || + if (!f2fs_realtime_discard_enable(sbi) || + (!se->valid_blocks && + !IS_CURSEG(sbi, cpc->trim_start)) || SM_I(sbi)->dcc_info->nr_discards >= SM_I(sbi)->dcc_info->max_discards) return false;
During a checkpoint, the current active segment X may not be handled properly. This occurs when segment X has 0 valid blocks and a non-zero number of discard blocks, for the following reasons: locate_dirty_segment() does not mark any active segment as a prefree segment. As a result, segment X is not included in dirty_segmap[PRE], and f2fs_clear_prefree_segments() skips it when handling prefree segments. add_discard_addrs() skips any segment with 0 valid blocks, so segment X is also skipped. Consequently, no `struct discard_cmd` is actually created for segment X. However, the ckpt_valid_map and cur_valid_map of segment X are synced by seg_info_to_raw_sit() during the current checkpoint process. As a result, it cannot find the missing discard bits even in subsequent checkpoints. Consequently, the value of sbi->discard_blks remains non-zero. Thus, when f2fs is umounted, CP_TRIMMED_FLAG will not be set due to the non-zero sbi->discard_blks. Relevant code process: f2fs_write_checkpoint() f2fs_flush_sit_entries() list_for_each_entry_safe(ses, tmp, head, set_list) { for_each_set_bit_from(segno, bitmap, end) { ... add_discard_addrs(sbi, cpc, false); // skip segment X due to its 0 valid blocks ... seg_info_to_raw_sit(); // sync ckpt_valid_map with cur_valid_map for segment X ... } } f2fs_clear_prefree_segments(); // segment X is not included in dirty_segmap[PRE] and is skipped Since add_discard_addrs() can handle active segments with non-zero valid blocks, it is reasonable to fix this issue by allowing it to also handle active segments with 0 valid blocks. Fixes: b29555505d81 ("f2fs: add key functions for small discards") Signed-off-by: Chunhai Guo <guochunhai@vivo.com> --- v1: https://lore.kernel.org/linux-f2fs-devel/20241203065108.2763436-1-guochunhai@vivo.com/ v1->v2: - Modify the commit message to make it easier to understand. - Add fixes to the commit. --- fs/f2fs/segment.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)