在 3/14/2025 6:38 PM, Chunhai Guo 写道: > 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, Could you please provide some advice on how to fix the above logic when you have a moment? Thanks, > > 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
