Re: [f2fs-dev] [PATCH] f2fs: accurately adjust free_sections during free_segment_range

[Chao Yu <chao@kernel.org>]

On 8/19/26 01:14, Daeho Jeong wrote:
> From: Daeho Jeong <daehojeong@google.com>
> 
> In free_segment_range(), MAIN_SECS(sbi) is temporarily reduced by `secs`
> while valid blocks in the truncated range are evacuated by GC.
> 
> However, if any sections within the truncated range were already free,
> failing to deduct them from FREE_I(sbi)->free_sections leads to an
> over-estimation of available space in the reduced main area, causing
> inconsistent free section accounting.
> 
> Fix this by calculating the number of already-free sections in the
> truncated range under segmap_lock, deducting them from free_sections upon
> entering free_segment_range(), and restoring them under segmap_lock on exit.

I think we need to change commit message a bit to reflect real issues?

Fixes and Cc stable line here.

> 
> Signed-off-by: Daeho Jeong <daehojeong@google.com>
> Signed-off-by: Sunmin Jeong <s_min.jeong@samsung.com>
> ---
>   fs/f2fs/gc.c | 15 ++++++++++++++-
>   1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index 787133ee2eb2..f3a6fc6d08ae 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -2200,8 +2200,9 @@ int f2fs_gc_range(struct f2fs_sb_info *sbi,
>   static int free_segment_range(struct f2fs_sb_info *sbi,
>   				unsigned int secs, bool dry_run)
>   {
> -	unsigned int next_inuse, start, end;
> +	unsigned int secno, next_inuse, start, end, end_secno;
>   	struct cp_control cpc = { CP_RESIZE, 0, 0, 0 };
> +	unsigned int freed_secs = 0;
>   	int gc_mode, gc_type;
>   	int err = 0;
>   	int type;
> @@ -2210,6 +2211,7 @@ static int free_segment_range(struct f2fs_sb_info *sbi,
>   	MAIN_SECS(sbi) -= secs;
>   	start = MAIN_SECS(sbi) * SEGS_PER_SEC(sbi);
>   	end = MAIN_SEGS(sbi) - 1;
> +	end_secno = GET_SEC_FROM_SEG(sbi, end);
>   
>   	mutex_lock(&DIRTY_I(sbi)->seglist_lock);
>   	for (gc_mode = 0; gc_mode < MAX_GC_POLICY; gc_mode++)
> @@ -2221,6 +2223,14 @@ static int free_segment_range(struct f2fs_sb_info *sbi,
>   			sbi->next_victim_seg[gc_type] = NULL_SEGNO;
>   	mutex_unlock(&DIRTY_I(sbi)->seglist_lock);
>   
> +	spin_lock(&FREE_I(sbi)->segmap_lock);
> +	for (secno = MAIN_SECS(sbi); secno <= end_secno; secno++) {
> +		if (!test_bit(secno, FREE_I(sbi)->free_secmap))
> +			freed_secs++;
> +	}
> +	FREE_I(sbi)->free_sections -= freed_secs;
> +	spin_unlock(&FREE_I(sbi)->segmap_lock);
> +

Before f2fs_gc_range
0..89 have 10 dirty/full sections, 80 free sections.
90..99 have 5 dirty sections, 5 free sections.

FREE_I(sbi)->free_sections -= freed_secs;
free_sections = 85 - 5 = 80

After f2fs_gc_range
0..89 have 13 dirty/full sections, 77 free sections.
90..99 have 10 free sections.
free_sections = 77 (.free_sections) + 10 (secs) = 87

>   	/* Move out cursegs from the target range */
>   	for (type = CURSEG_HOT_DATA; type < NR_CURSEG_TYPE; type++) {
>   		err = f2fs_allocate_segment_for_resize(sbi, type, start, end);
> @@ -2245,6 +2255,9 @@ static int free_segment_range(struct f2fs_sb_info *sbi,
>   		f2fs_bug_on(sbi, 1);
>   	}
>   out:
> +	spin_lock(&FREE_I(sbi)->segmap_lock);
> +	FREE_I(sbi)->free_sections += freed_secs;

So, shouldn't be?
FREE_I(sbi)->free_sections += secs;

Thanks,

> +	spin_unlock(&FREE_I(sbi)->segmap_lock);
>   	MAIN_SECS(sbi) += secs;
>   	return err;
>   }