Re: [f2fs-dev] [PATCH v2 2/2] f2fs: introduce get_section_mtime

[Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

On 2024/9/12 14:40, liuderong@oppo.com wrote:
> From: liuderong <liuderong@oppo.com>
> 
> When segs_per_sec is larger than 1, section may contain free segments,
> mtime should be the mean value of each valid segments,
> so introduce get_section_mtime to exclude free segments in a section.
> 
> Signed-off-by: liuderong <liuderong@oppo.com>
> ---
>   fs/f2fs/f2fs.h    |  2 ++
>   fs/f2fs/gc.c      | 15 ++-------------
>   fs/f2fs/segment.c | 41 ++++++++++++++++++++++++++++++++++++-----
>   3 files changed, 40 insertions(+), 18 deletions(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 4dcdcdd..d6adf0f 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -3762,6 +3762,8 @@ enum rw_hint f2fs_io_type_to_rw_hint(struct f2fs_sb_info *sbi,
>   unsigned int f2fs_usable_segs_in_sec(struct f2fs_sb_info *sbi);
>   unsigned int f2fs_usable_blks_in_seg(struct f2fs_sb_info *sbi,
>   			unsigned int segno);
> +unsigned long long get_section_mtime(struct f2fs_sb_info *sbi,
> +			unsigned int segno);

Hi Derong,

It needs to add "f2fs_" prefix for get_section_mtime() to avoid global
namespace pollution.

>   
>   #define DEF_FRAGMENT_SIZE	4
>   #define MIN_FRAGMENT_SIZE	1
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index 6299639..03c6117 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -332,20 +332,14 @@ static unsigned int check_bg_victims(struct f2fs_sb_info *sbi)
>   static unsigned int get_cb_cost(struct f2fs_sb_info *sbi, unsigned int segno)
>   {
>   	struct sit_info *sit_i = SIT_I(sbi);
> -	unsigned int secno = GET_SEC_FROM_SEG(sbi, segno);
> -	unsigned int start = GET_SEG_FROM_SEC(sbi, secno);
>   	unsigned long long mtime = 0;
>   	unsigned int vblocks;
>   	unsigned char age = 0;
>   	unsigned char u;
> -	unsigned int i;
>   	unsigned int usable_segs_per_sec = f2fs_usable_segs_in_sec(sbi);
>   
> -	for (i = 0; i < usable_segs_per_sec; i++)
> -		mtime += get_seg_entry(sbi, start + i)->mtime;
> +	mtime = get_section_mtime(sbi, segno);
>   	vblocks = get_valid_blocks(sbi, segno, true);
> -
> -	mtime = div_u64(mtime, usable_segs_per_sec);
>   	vblocks = div_u64(vblocks, usable_segs_per_sec);
>   
>   	u = BLKS_TO_SEGS(sbi, vblocks * 100);
> @@ -485,10 +479,7 @@ static void add_victim_entry(struct f2fs_sb_info *sbi,
>   				struct victim_sel_policy *p, unsigned int segno)
>   {
>   	struct sit_info *sit_i = SIT_I(sbi);
> -	unsigned int secno = GET_SEC_FROM_SEG(sbi, segno);
> -	unsigned int start = GET_SEG_FROM_SEC(sbi, secno);
>   	unsigned long long mtime = 0;
> -	unsigned int i;
>   
>   	if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED))) {
>   		if (p->gc_mode == GC_AT &&
> @@ -496,9 +487,7 @@ static void add_victim_entry(struct f2fs_sb_info *sbi,
>   			return;
>   	}
>   
> -	for (i = 0; i < SEGS_PER_SEC(sbi); i++)
> -		mtime += get_seg_entry(sbi, start + i)->mtime;
> -	mtime = div_u64(mtime, SEGS_PER_SEC(sbi));
> +	mtime = get_section_mtime(sbi, segno);
>   
>   	/* Handle if the system time has changed by the user */
>   	if (mtime < sit_i->min_mtime)
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 6627394..e62e722 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -5389,6 +5389,41 @@ unsigned int f2fs_usable_segs_in_sec(struct f2fs_sb_info *sbi)
>   	return SEGS_PER_SEC(sbi);
>   }
>   
> +unsigned long long get_section_mtime(struct f2fs_sb_info *sbi,
> +	unsigned int segno)
> +{
> +	unsigned int usable_segs_per_sec = f2fs_usable_segs_in_sec(sbi);
> +	unsigned int secno = 0, start = 0;
> +	struct free_segmap_info *free_i = FREE_I(sbi);
> +	unsigned int valid_seg_count = 0;
> +	unsigned long long mtime = 0;
> +	unsigned int i = 0;
> +
> +	if (segno == NULL_SEGNO)
> +		return 0;

No needed.

> +
> +	secno = GET_SEC_FROM_SEG(sbi, segno);
> +	start = GET_SEG_FROM_SEC(sbi, secno);
> +
> +	if (!__is_large_section(sbi))
> +		return get_seg_entry(sbi, start + i)->mtime;
> +
> +	for (i = 0; i < usable_segs_per_sec; i++) {
> +		/* for large section, only check the mtime of valid segments */
> +		spin_lock(&free_i->segmap_lock);
> +		if (test_bit(start + i, free_i->free_segmap)) {
> +			mtime += get_seg_entry(sbi, start + i)->mtime;
> +			valid_seg_count++;
> +		}
> +		spin_unlock(&free_i->segmap_lock);
> +	}

After commit 6f3a01ae9b72 ("f2fs: record average update time of segment"),
mtime of segment starts to indicate average update time of segment.

So it needs to change like this?

for (i = 0; i < usable_segs_per_sec; i++) {
	struct seg_entry *se = get_seg_entry(sbi, start + i);

	mtime += se->mtime * se->valid_blocks;
	total_valid_blocks += se->valid_blocks;
}

if (total_valid_blocks == 0)
	return 0;

return div_u64(mtime, total_valid_blocks);

Thanks,

> +
> +	if (valid_seg_count == 0)
> +		return 0;
> +
> +	return div_u64(mtime, valid_seg_count);
> +}
> +
>   /*
>    * Update min, max modified time for cost-benefit GC algorithm
>    */
> @@ -5402,13 +5437,9 @@ static void init_min_max_mtime(struct f2fs_sb_info *sbi)
>   	sit_i->min_mtime = ULLONG_MAX;
>   
>   	for (segno = 0; segno < MAIN_SEGS(sbi); segno += SEGS_PER_SEC(sbi)) {
> -		unsigned int i;
>   		unsigned long long mtime = 0;
>   
> -		for (i = 0; i < SEGS_PER_SEC(sbi); i++)
> -			mtime += get_seg_entry(sbi, segno + i)->mtime;
> -
> -		mtime = div_u64(mtime, SEGS_PER_SEC(sbi));
> +		mtime = get_section_mtime(sbi, segno);
>   
>   		if (sit_i->min_mtime > mtime)
>   			sit_i->min_mtime = mtime;



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