RE: [PATCH v2 2/2] exfat: hint the empty entry which at the end of cluster chain

[Sungjong Seo]

> After traversing all directory entries, hint the empty directory
> entry no matter whether or not there are enough empty directory
> entries.
> 
> After this commit, hint the empty directory entries like this:
> 
> 1. Hint the deleted directory entries if enough;
> 2. Hint the deleted and unused directory entries which at the
>    end of the cluster chain no matter whether enough or not(Add
>    by this commit);
> 3. If no any empty directory entries, hint the empty directory
>    entries in the new cluster(Add by this commit).
> 
> This avoids repeated traversal of directory entries, reduces CPU
> usage, and improves the performance of creating files and
> directories(especially on low-performance CPUs).
> 
> Test create 5000 files in a class 4 SD card on imx6q-sabrelite
> with:
> 
> for ((i=0;i<5;i++)); do
>    sync
>    time (for ((j=1;j<=1000;j++)); do touch file$((i*1000+j)); done)
> done
> 
> The more files, the more performance improvements.
> 
>             Before   After    Improvement
>    1~1000   25.360s  22.168s  14.40%
> 1001~2000   38.242s  28.72ss  33.15%
> 2001~3000   49.134s  35.037s  40.23%
> 3001~4000   62.042s  41.624s  49.05%
> 4001~5000   73.629s  46.772s  57.42%
> 
> Signed-off-by: Yuezhang Mo <Yuezhang.Mo@xxxxxxxx>
> Reviewed-by: Andy Wu <Andy.Wu@xxxxxxxx>
> Reviewed-by: Aoyama Wataru <wataru.aoyama@xxxxxxxx>

Reviewed-by: Sungjong Seo <sj1557.seo@xxxxxxxxxxx>

Looks good. Thanks!

> ---
>  fs/exfat/dir.c   | 26 ++++++++++++++++++++++----
>  fs/exfat/namei.c | 33 +++++++++++++++++++++------------
>  2 files changed, 43 insertions(+), 16 deletions(-)
> 
> diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c
> index 9f9b8435baca..5497a610808d 100644
> --- a/fs/exfat/dir.c
> +++ b/fs/exfat/dir.c
> @@ -905,17 +905,24 @@ static inline void exfat_reset_empty_hint(struct
> exfat_hint_femp *hint_femp)
> 
>  static inline void exfat_set_empty_hint(struct exfat_inode_info *ei,
>  		struct exfat_hint_femp *candi_empty, struct exfat_chain *clu,
> -		int dentry, int num_entries)
> +		int dentry, int num_entries, int entry_type)
>  {
>  	if (ei->hint_femp.eidx == EXFAT_HINT_NONE ||
>  	    ei->hint_femp.eidx > dentry) {
> +		int total_entries = EXFAT_B_TO_DEN(i_size_read(&ei-
> >vfs_inode));
> +
>  		if (candi_empty->count == 0) {
>  			candi_empty->cur = *clu;
>  			candi_empty->eidx = dentry;
>  		}
> 
> -		candi_empty->count++;
> -		if (candi_empty->count == num_entries)
> +		if (entry_type == TYPE_UNUSED)
> +			candi_empty->count += total_entries - dentry;
> +		else
> +			candi_empty->count++;
> +
> +		if (candi_empty->count == num_entries ||
> +		    candi_empty->count + candi_empty->eidx == total_entries)
>  			ei->hint_femp = *candi_empty;
>  	}
>  }
> @@ -989,7 +996,8 @@ int exfat_find_dir_entry(struct super_block *sb,
> struct exfat_inode_info *ei,
>  				step = DIRENT_STEP_FILE;
> 
>  				exfat_set_empty_hint(ei, &candi_empty, &clu,
> -						dentry, num_entries);
> +						dentry, num_entries,
> +						entry_type);
> 
>  				brelse(bh);
>  				if (entry_type == TYPE_UNUSED)
> @@ -1100,6 +1108,16 @@ int exfat_find_dir_entry(struct super_block *sb,
> struct exfat_inode_info *ei,
>  		goto rewind;
>  	}
> 
> +	/*
> +	 * set the EXFAT_EOF_CLUSTER flag to avoid search
> +	 * from the beginning again when allocated a new cluster
> +	 */
> +	if (ei->hint_femp.eidx == EXFAT_HINT_NONE) {
> +		ei->hint_femp.cur.dir = EXFAT_EOF_CLUSTER;
> +		ei->hint_femp.eidx = p_dir->size * dentries_per_clu;
> +		ei->hint_femp.count = 0;
> +	}
> +
>  	/* initialized hint_stat */
>  	hint_stat->clu = p_dir->dir;
>  	hint_stat->eidx = 0;
> diff --git a/fs/exfat/namei.c b/fs/exfat/namei.c
> index b617bebc3d0f..add4893711d3 100644
> --- a/fs/exfat/namei.c
> +++ b/fs/exfat/namei.c
> @@ -224,11 +224,18 @@ static int exfat_search_empty_slot(struct
> super_block *sb,
> 
>  	if (hint_femp->eidx != EXFAT_HINT_NONE) {
>  		dentry = hint_femp->eidx;
> -		if (num_entries <= hint_femp->count) {
> -			hint_femp->eidx = EXFAT_HINT_NONE;
> -			return dentry;
> -		}
> 
> +		/*
> +		 * If hint_femp->count is enough, it is needed to check if
> +		 * there are actual empty entries.
> +		 * Otherwise, and if "dentry + hint_famp->count" is also
> equal
> +		 * to "p_dir->size * dentries_per_clu", it means ENOSPC.
> +		 */
> +		if (dentry + hint_femp->count == p_dir->size *
> dentries_per_clu
> +		    && num_entries > hint_femp->count)
> +			return -ENOSPC;
> +
> +		hint_femp->eidx = EXFAT_HINT_NONE;
>  		exfat_chain_dup(&clu, &hint_femp->cur);
>  	} else {
>  		exfat_chain_dup(&clu, p_dir);
> @@ -293,6 +300,12 @@ static int exfat_search_empty_slot(struct super_block
> *sb,
>  		}
>  	}
> 
> +	hint_femp->eidx = p_dir->size * dentries_per_clu - num_empty;
> +	hint_femp->count = num_empty;
> +	if (num_empty == 0)
> +		exfat_chain_set(&hint_femp->cur, EXFAT_EOF_CLUSTER, 0,
> +				clu.flags);
> +
>  	return -ENOSPC;
>  }
> 
> @@ -369,15 +382,11 @@ static int exfat_find_empty_entry(struct inode
> *inode,
>  			if (exfat_ent_set(sb, last_clu, clu.dir))
>  				return -EIO;
> 
> -		if (hint_femp.eidx == EXFAT_HINT_NONE) {
> -			/* the special case that new dentry
> -			 * should be allocated from the start of new cluster
> -			 */
> -			hint_femp.eidx = EXFAT_B_TO_DEN_IDX(p_dir->size, sbi);
> -			hint_femp.count = sbi->dentries_per_clu;
> -
> +		if (hint_femp.cur.dir == EXFAT_EOF_CLUSTER)
>  			exfat_chain_set(&hint_femp.cur, clu.dir, 0, clu.flags);
> -		}
> +
> +		hint_femp.count += sbi->dentries_per_clu;
> +
>  		hint_femp.cur.size++;
>  		p_dir->size++;
>  		size = EXFAT_CLU_TO_B(p_dir->size, sbi);
> --
> 2.25.1