Re: [PATCH RFC 2/5] f2fs: record average update time of segment

Jaegeuk Kim
2020-07-01T16:19:31Z

On 06/30, Chao Yu wrote:
> Previously, once we update one block in segment, we will update mtime of
> segment to last time, making aged segment becoming freshest, result in
> that GC with cost benefit algorithm missing such segment, So this patch
> changes to record mtime as average block updating time instead of last
> updating time.
>
> It's not needed to reset mtime for prefree segment, as se->valid_blocks
> is zero, then old se->mtime won't take any weight with below calculation:
>
> se->mtime = (se->mtime * se->valid_blocks + mtime) /
> (se->valid_blocks + 1);
>
> Signed-off-by: Chao Yu <yuchao0@huawei.com>
> ---
> fs/f2fs/segment.c | 21 ++++++++++++++++++---
> 1 file changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 863ec6f1fb87..906c313835ad 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -2150,6 +2150,22 @@ static void __set_sit_entry_type(struct f2fs_sb_info *sbi, int type,
> __mark_sit_entry_dirty(sbi, segno);
> }
>
> +static void update_segment_mtime(struct f2fs_sb_info *sbi, block_t blkaddr)
> +{
> + unsigned int segno = GET_SEGNO(sbi, blkaddr);
> + struct seg_entry *se = get_seg_entry(sbi, segno);
> + unsigned long long mtime = get_mtime(sbi, false);
> +
> + if (!se->mtime) {

Don't need {}.

> + se->mtime = mtime;
> + } else {
> + se->mtime = (se->mtime * se->valid_blocks + mtime) /
> + (se->valid_blocks + 1);
> + }
> + if (mtime > SIT_I(sbi)->max_mtime)
> + SIT_I(sbi)->max_mtime = mtime;
> +}
> +
> static void update_sit_entry(struct f2fs_sb_info *sbi, block_t blkaddr, int del)
> {
> struct seg_entry *se;
> @@ -2169,10 +2185,9 @@ static void update_sit_entry(struct f2fs_sb_info *sbi, block_t blkaddr, int del)
> f2fs_bug_on(sbi, (new_vblocks >> (sizeof(unsigned short) << 3) ||
> (new_vblocks > sbi->blocks_per_seg)));
>
> + update_segment_mtime(sbi, blkaddr);
> +
> se->valid_blocks = new_vblocks;
> - se->mtime = get_mtime(sbi, false);
> - if (se->mtime > SIT_I(sbi)->max_mtime)
> - SIT_I(sbi)->max_mtime = se->mtime;
>
> /* Update valid block bitmap */
> if (del > 0) {
> --
> 2.26.2