Re: [f2fs-dev] [PATCH 1/3] f2fs-tools: give less overprovisioning space

[Jaegeuk Kim <jaegeuk@kernel.org>]

On 10/20, Shinichiro Kawasaki wrote:
> On Oct 10, 2022 / 15:15, Jaegeuk Kim wrote:
> > As f2fs becomes more resilient for GCs, let's give the marginal overprovision
> > space back to user.
> > 
> > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> 
> Hello Jaegeuk,
> 
> Using the dev branch of f2fs-tools repo, I observed mkfs.f2fs failure with zoned
> block devices:
> 
>         Error: Device size is not sufficient for F2FS volume
> 
> I found this patch in the branch triggers it. I also observed the same failure
> is observed with non- zoned regular block devices when I specify -s options to
> mkfs.f2fs command. With these conditions, number of segments in each section is
> not zero, and it increases the number of reserved segments. My understanding is
> that it makes reserved segments larger than overprovisioning segments all the
> time in the loop of get_best_overprovision(). Then get_best_overprovision()
> returns 0% overprovisioning ratio. Hence the error.
> 
> Could you take a look for fix?

Thanks, I think that fix looks good to me. I applied into the original patch.
https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs-tools.git/commit/?h=dev&id=281d3e72370f6c39c0d57acaf37a7f0e003ddd28

> 
> FYI, I tried to fix and created a patch which allows reserved segments larger
> than overprovisioning segments [1]. It compares those two, and take larger one
> to subtract from usable segments to get the segments for users. I confirmed it
> keeps small number of overprovisioning segments for no -s option case, and
> avoids the mkfs.f2fs failure for the -s option and zoned block device cases.
> However, it increases runtime of my test script which fills f2fs and do file
> overwrites to test f2fs GC on zoned block devices. It takes +60% longer runtime.
> Then GC performance looks worse than before, and this fix does not look good
> for me.

I think you can try to avoid that by tuning /sys/fs/f2fs/xx/reserved_blocks?

> 
> [1]
> 
> diff --git a/include/f2fs_fs.h b/include/f2fs_fs.h
> index 8ca574a..4902953 100644
> --- a/include/f2fs_fs.h
> +++ b/include/f2fs_fs.h
> @@ -1634,9 +1634,10 @@ static inline double get_best_overprovision(struct f2fs_super_block *sb)
>  		reserved = (100 / candidate + 1 + NR_CURSEG_TYPE) *
>  				round_up(usable_main_segs, get_sb(section_count));
>  		ovp = (usable_main_segs - reserved) * candidate / 100;
> -		if (reserved >= ovp)
> +		if (ovp < 0)
>  			continue;
> -		space = usable_main_segs - ovp;
> +
> +		space = usable_main_segs - max(reserved, ovp);
>  		if (max_space < space) {
>  			max_space = space;
>  			max_ovp = candidate;
> diff --git a/mkfs/f2fs_format.c b/mkfs/f2fs_format.c
> index c314d1c..08f4e66 100644
> --- a/mkfs/f2fs_format.c
> +++ b/mkfs/f2fs_format.c
> @@ -764,11 +764,8 @@ static int f2fs_write_check_point_pack(void)
>  	set_cp(overprov_segment_count, (f2fs_get_usable_segments(sb) -
>  			get_cp(rsvd_segment_count)) *
>  			c.overprovision / 100);
> -
> -	if (get_cp(rsvd_segment_count) > get_cp(overprov_segment_count)) {
> -		MSG(0, "\tError: Wrong overprovision ratio\n");
> -		goto free_cp_payload;
> -	}
> +	if (get_cp(overprov_segment_count) < get_cp(rsvd_segment_count))
> +		set_cp(overprov_segment_count, get_cp(rsvd_segment_count));
>  
>  	if (f2fs_get_usable_segments(sb) <= get_cp(overprov_segment_count)) {
>  		MSG(0, "\tError: Not enough segments to create F2FS Volume\n");
> 
> -- 
> Shin'ichiro Kawasaki


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