在 3/12/2025 10:27 PM, Jaegeuk Kim 写道: > On 03/12, Chunhai Guo wrote: >> fstrim may miss candidates that need to be discarded, as shown in the >> examples below. >> >> The root cause is that when cpc->reason is set with CP_DISCARD, >> add_discard_addrs() expects that ckpt_valid_map and cur_valid_map have >> been synced by seg_info_to_raw_sit() [1], and it tries to find the >> candidates based on ckpt_valid_map and discard_map. However, >> seg_info_to_raw_sit() does not actually run before >> f2fs_exist_trim_candidates(), resulting in the failure. > I think we need to fix the above logic.
Hi Jaegeuk, I initially attempted to address this issue by checking whether seg_info_to_raw_sit() runs before add_discard_addrs(). The implementation can be found in the V1 patch here: https://lore.kernel.org/linux-f2fs-devel/20250102101310.580277-1-guochun...@vivo.com/ However, after discussing with Chao, I realized that perhaps a better way is to find all the discard blocks based only on discard_map. This approach is much simpler and makes add_discard_addrs() independent of the pre-run of seg_info_to_raw_sit(). Could you please detail your opinion? Thanks, >> The code logic can be simplified for all cases by finding all the >> discard blocks based only on discard_map. This might result in more >> discard blocks being sent for the segment during the first checkpoint >> after mounting, which were originally expected to be sent only in >> fstrim. Regardless, these discard blocks should eventually be sent, and >> the simplified code makes sense in this context. >> >> root# cp testfile /f2fs_mountpoint >> >> root# f2fs_io fiemap 0 1 /f2fs_mountpoint/testfile >> Fiemap: offset = 0 len = 1 >> logical addr. physical addr. length flags >> 0 0000000000000000 0000000406a00000 000000003d800000 00001000 >> >> root# rm /f2fs_mountpoint/testfile >> >> root# fstrim -v -o 0x406a00000 -l 1024M /f2fs_mountpoint -- no candidate is >> found >> /f2fs_mountpoint: 0 B (0 bytes) trimmed >> >> Relevant code process of the root cause: >> f2fs_trim_fs() >> f2fs_write_checkpoint() >> ... >> if (cpc->reason & CP_DISCARD) { >> if (!f2fs_exist_trim_candidates(sbi, cpc)) { >> unblock_operations(sbi); >> goto out; // No candidates are found here, and it exits. >> } >> ... >> } >> >> [1] Please refer to commit d7bc2484b8d4 ("f2fs: fix small discards not >> to issue redundantly") for the relationship between >> seg_info_to_raw_sit() and add_discard_addrs(). >> >> Fixes: 25290fa5591d ("f2fs: return fs_trim if there is no candidate") >> Signed-off-by: Chunhai Guo <guochun...@vivo.com> >> --- >> v2->v3: Add f2fs_bug_on() to make sure it never issues discard to valid >> data's block address. >> v1->v2: Find all the discard blocks based only on discard_map in >> add_discard_addrs(). >> v1: >> https://lore.kernel.org/linux-f2fs-devel/20250102101310.580277-1-guochun...@vivo.com/ >> --- >> fs/f2fs/segment.c | 8 ++++---- >> 1 file changed, 4 insertions(+), 4 deletions(-) >> >> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c >> index 86e547f008f9..c8ad8e3bfebb 100644 >> --- a/fs/f2fs/segment.c >> +++ b/fs/f2fs/segment.c >> @@ -2075,7 +2075,6 @@ static bool add_discard_addrs(struct f2fs_sb_info >> *sbi, struct cp_control *cpc, >> int entries = SIT_VBLOCK_MAP_SIZE / sizeof(unsigned long); >> struct seg_entry *se = get_seg_entry(sbi, cpc->trim_start); >> unsigned long *cur_map = (unsigned long *)se->cur_valid_map; >> - unsigned long *ckpt_map = (unsigned long *)se->ckpt_valid_map; >> unsigned long *discard_map = (unsigned long *)se->discard_map; >> unsigned long *dmap = SIT_I(sbi)->tmp_map; >> unsigned int start = 0, end = -1; >> @@ -2097,9 +2096,10 @@ static bool add_discard_addrs(struct f2fs_sb_info >> *sbi, struct cp_control *cpc, >> } >> >> /* SIT_VBLOCK_MAP_SIZE should be multiple of sizeof(unsigned long) */ >> - for (i = 0; i < entries; i++) >> - dmap[i] = force ? ~ckpt_map[i] & ~discard_map[i] : >> - (cur_map[i] ^ ckpt_map[i]) & ckpt_map[i]; >> + for (i = 0; i < entries; i++) { >> + dmap[i] = ~discard_map[i]; >> + f2fs_bug_on(sbi, (cur_map[i] ^ discard_map[i]) & cur_map[i]); >> + } >> >> while (force || SM_I(sbi)->dcc_info->nr_discards <= >> SM_I(sbi)->dcc_info->max_discards) { >> -- >> 2.34.1 _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
