RE: [RFC PATCH] exfat: optimize performance of deleting a file

["Sungjong Seo" <sj1557.seo@samsung.com>]

Hello, Jun,

Perhaps you are looking at an old version of the exfat code.
The performance of exfat_free_cluster has been improved in the latest
version. I think the below commit could help you.

f728760aa923 ("exfat: improve performance of exfat_free_cluster when
using dirsync mount option")

Thanks.

> When a large file is deleted, it's cluster bitmap is cleared.
> After a bit is cleared, the buffer_head is synced.
> A buffer_head can be synced many times repeatedly.
> We can clear all bits first and then sync all buffer_heads.
> So each buffer_head is synced only once, which significantly improves
> performance.
> 
> In my test, It takes about 2 minitues to delete a 5GB file without the
> patch.
> After applying the patch, the file is deleted in almost less than 1s.
> 
> Signed-off-by: Jun <hljhnu@gmail.com>
> Change-Id: I7637032db04042b8ad1ca73fe7db09d43a253255
> ---
>  fs/exfat/balloc.c   | 28 ++++++++++++++++++++++++++--
>  fs/exfat/exfat_fs.h |  2 ++
>  fs/exfat/fatent.c   | 45 +++++++++++++++++++++++++++++++++++++++++----
>  3 files changed, 69 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/exfat/balloc.c b/fs/exfat/balloc.c index
> 579c10f57c2b..58bdfb58bf1d 100644
> --- a/fs/exfat/balloc.c
> +++ b/fs/exfat/balloc.c
> @@ -164,7 +164,6 @@ void exfat_clear_bitmap(struct inode *inode, unsigned
> int clu)
>  	unsigned int ent_idx;
>  	struct super_block *sb = inode->i_sb;
>  	struct exfat_sb_info *sbi = EXFAT_SB(sb);
> -	struct exfat_mount_options *opts = &sbi->options;
> 
>  	WARN_ON(clu < EXFAT_FIRST_CLUSTER);
>  	ent_idx = CLUSTER_TO_BITMAP_ENT(clu);
> @@ -172,7 +171,32 @@ void exfat_clear_bitmap(struct inode *inode, unsigned
> int clu)
>  	b = BITMAP_OFFSET_BIT_IN_SECTOR(sb, ent_idx);
> 
>  	clear_bit_le(b, sbi->vol_amap[i]->b_data);
> -	exfat_update_bh(sbi->vol_amap[i], IS_DIRSYNC(inode));
> +	set_buffer_uptodate(sbi->vol_amap[i]);
> +	mark_buffer_dirty(sbi->vol_amap[i]);
> +}
> +
> +void exfat_wait_bitmap(struct inode *inode, unsigned int clu) {
> +	int i;
> +	unsigned int ent_idx;
> +	struct super_block *sb = inode->i_sb;
> +	struct exfat_sb_info *sbi = EXFAT_SB(sb);
> +
> +	WARN_ON(clu < EXFAT_FIRST_CLUSTER);
> +	ent_idx = CLUSTER_TO_BITMAP_ENT(clu);
> +	i = BITMAP_OFFSET_SECTOR_INDEX(sb, ent_idx);
> +
> +	if (IS_DIRSYNC(inode))
> +		sync_dirty_buffer(sbi->vol_amap[i]);
> +}
> +
> +void exfat_discard_cluster(struct inode *inode, unsigned int clu) {
> +	struct super_block *sb = inode->i_sb;
> +	struct exfat_sb_info *sbi = EXFAT_SB(sb);
> +	struct exfat_mount_options *opts = &sbi->options;
> +
> +	WARN_ON(clu < EXFAT_FIRST_CLUSTER);
> 
>  	if (opts->discard) {
>  		int ret_discard;
> diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h index
> b8f0e829ecbd..1ecd2379022d 100644
> --- a/fs/exfat/exfat_fs.h
> +++ b/fs/exfat/exfat_fs.h
> @@ -409,6 +409,8 @@ int exfat_load_bitmap(struct super_block *sb);  void
> exfat_free_bitmap(struct exfat_sb_info *sbi);  int exfat_set_bitmap(struct
> inode *inode, unsigned int clu);  void exfat_clear_bitmap(struct inode
> *inode, unsigned int clu);
> +void exfat_wait_bitmap(struct inode *inode, unsigned int clu); void
> +exfat_discard_cluster(struct inode *inode, unsigned int clu);
>  unsigned int exfat_find_free_bitmap(struct super_block *sb, unsigned int
> clu);  int exfat_count_used_clusters(struct super_block *sb, unsigned int
> *ret_count);
> 
> diff --git a/fs/exfat/fatent.c b/fs/exfat/fatent.c index
> c3c9afee7418..f39a912a7da7 100644
> --- a/fs/exfat/fatent.c
> +++ b/fs/exfat/fatent.c
> @@ -183,19 +183,56 @@ int exfat_free_cluster(struct inode *inode, struct
> exfat_chain *p_chain)
> 
>  			num_clusters++;
>  		} while (num_clusters < p_chain->size);
> +		sbi->used_clusters -= num_clusters;
> +
> +		clu = p_chain->dir;
> +		num_clusters = 0;
> +		do {
> +			exfat_wait_bitmap(inode, clu);
> +			clu++;
> +
> +			num_clusters++;
> +		} while (num_clusters < p_chain->size);
> +
> +		clu = p_chain->dir;
> +		num_clusters = 0;
> +		do {
> +			exfat_discard_cluster(inode, clu);
> +			clu++;
> +
> +			num_clusters++;
> +		} while (num_clusters < p_chain->size);
> +
>  	} else {
>  		do {
>  			exfat_clear_bitmap(inode, clu);
> 
>  			if (exfat_get_next_cluster(sb, &clu))
> -				goto dec_used_clus;
> +				goto exit;
> +
> +			sbi->used_clusters--;
> +		} while (clu != EXFAT_EOF_CLUSTER);
> +
> +		clu = p_chain->dir;
> +		do {
> +			exfat_wait_bitmap(inode, clu);
> +
> +			if (exfat_get_next_cluster(sb, &clu))
> +				goto exit;
> +
> +		} while (clu != EXFAT_EOF_CLUSTER);
> +
> +		clu = p_chain->dir;
> +		do {
> +			exfat_discard_cluster(inode, clu);
> +
> +			if (exfat_get_next_cluster(sb, &clu))
> +				goto exit;
> 
> -			num_clusters++;
>  		} while (clu != EXFAT_EOF_CLUSTER);
>  	}
> 
> -dec_used_clus:
> -	sbi->used_clusters -= num_clusters;
> +exit:
>  	return 0;
>  }
> 
> --
> 2.36.1