On 3/12/25 11:19, Chunhai Guo wrote:
> 在 1/20/2025 7:45 PM, Chao Yu 写道:
>> On 1/19/25 22:08, 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.
>>>
>>> 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>
>>> ---
>>> v1:
>>> https://lore.kernel.org/linux-f2fs-devel/20250102101310.580277-1-guochun...@vivo.com/
>>> v1->v2: Find all the discard blocks based only on discard_map in
>>> add_discard_addrs().
>>> ---
>>> fs/f2fs/segment.c | 5 +----
>>> 1 file changed, 1 insertion(+), 4 deletions(-)
>>>
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index 13ee73a3c481..25ea892a42dd 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -2074,8 +2074,6 @@ 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;
>>> @@ -2100,8 +2098,7 @@ 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];
>>> + dmap[i] = ~discard_map[i];
>> discard is critical, we need more sanity check here, maybe:
>>
>> /* never issue discard to valid data's block address */
>> f2fs_bug_on(sbi, (cur_map[i] ^ discard_map[i]) & cur_map[i]);
>>
>> Can you please check this?
>
> Sure. I have added the BUG_ON check and performed the following tests
> without issue:
> 1. Ran xfstests and fsstress in the QEMU environment.
>
> 2. Ran monkey and reboot tests on ARM64 Android devices with the 6.6 kernel.
Thanks, so it looks fine now, can you please update the patch w/ above
f2fs_bug_on check?
Thanks,
>
> Thanks,
>
>
>>
>> Thanks,
>>
>>>
>>> while (force || SM_I(sbi)->dcc_info->nr_discards <=
>>> SM_I(sbi)->dcc_info->max_discards) {
>
>
_______________________________________________
Linux-f2fs-devel mailing list
Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
