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 <guochun...@vivo.com> --- v1: https://lore.kernel.org/linux-f2fs-devel/20241203065108.2763436-1-guochun...@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;
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