Re: [PATCH 2/2] f2fs: fix missing small discard in fstrim

[Chao Yu]

On 2025/1/2 18:13, Chunhai Guo wrote:
> If userspace issues an fstrim with a range that does not include all
> segments with small discards, these segments will be reused without being

I didn't get it, if fstrim didn't cover those segments, why do we need to
issue small discard for out-of-range segments?

Thanks,

> discarded. This patch fixes this issue.
> This patch is somewhat similar to commit 650d3c4e56e1 ("f2fs: fix a missing
> discard prefree segments").
>
> Fixes: d7bc2484b8d4 ("f2fs: fix small discards not to issue redundantly")
> Signed-off-by: Chunhai Guo <guochunhai@xxxxxxxx>
> ---
>   fs/f2fs/segment.c | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 8fe9f794b581..af9a62591c49 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -4552,6 +4552,8 @@ void f2fs_flush_sit_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc)
>   	struct list_head *head = &SM_I(sbi)->sit_entry_set;
>   	bool to_journal = !is_sbi_flag_set(sbi, SBI_IS_RESIZEFS);
>   	struct seg_entry *se;
> +	bool force = (cpc->reason & CP_DISCARD);
> +	__u64 trim_start = cpc->trim_start;
>   
>   	down_write(&sit_i->sentry_lock);
>   
> @@ -4609,7 +4611,9 @@ void f2fs_flush_sit_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc)
>   #endif
>   
>   			/* add discard candidates */
> -			if (!(cpc->reason & CP_DISCARD)) {
> +			if (!force || (force &&
> +					(segno < trim_start ||
> +					 segno > cpc->trim_end))) {
>   				cpc->trim_start = segno;
>   				add_discard_addrs(sbi, cpc, false, false);
>   			}
> @@ -4649,8 +4653,8 @@ void f2fs_flush_sit_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc)
>   	f2fs_bug_on(sbi, !list_empty(head));
>   	f2fs_bug_on(sbi, sit_i->dirty_sentries);
>   out:
> -	if (cpc->reason & CP_DISCARD) {
> -		__u64 trim_start = cpc->trim_start;
> +	if (force) {
> +		cpc->trim_start = trim_start;
>   
>   		for (; cpc->trim_start <= cpc->trim_end; cpc->trim_start++)
>   			add_discard_addrs(sbi, cpc, true, false);