Re: [PATCH 2/2] erofs: support to readahead dirent blocks in erofs_readdir()

[Gao Xiang <hsiangkao@linux.alibaba.com>]

Hi Chao,

On 2025/7/10 15:36, Chao Yu wrote:
> This patch supports to readahead more blocks in erofs_readdir(),
> it can enhance performance in large direcotry.
> 
> readdir test in a large directory which contains 12000 sub-files.
> 
> 		files_per_second
> Before:		926385.54
> After:		2380435.562
> 
> Signed-off-by: Chao Yu <chao@kernel.org>
> ---
>   fs/erofs/dir.c      | 8 ++++++++
>   fs/erofs/internal.h | 3 +++
>   2 files changed, 11 insertions(+)
> 
> diff --git a/fs/erofs/dir.c b/fs/erofs/dir.c
> index cff61c5a172b..04113851fc0f 100644
> --- a/fs/erofs/dir.c
> +++ b/fs/erofs/dir.c
> @@ -47,8 +47,10 @@ static int erofs_readdir(struct file *f, struct dir_context *ctx)
>   	struct inode *dir = file_inode(f);
>   	struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
>   	struct super_block *sb = dir->i_sb;
> +	struct file_ra_state *ra = &f->f_ra;
>   	unsigned long bsz = sb->s_blocksize;
>   	unsigned int ofs = erofs_blkoff(sb, ctx->pos);
> +	unsigned long nr_pages = DIV_ROUND_UP_POW2(dir->i_size, PAGE_SIZE);
>   	int err = 0;
>   	bool initial = true;
>   
> @@ -65,6 +67,12 @@ static int erofs_readdir(struct file *f, struct dir_context *ctx)
>   		}
>   		cond_resched();
>   
> +		/* readahead blocks to enhance performance in large directory */
> +		if (nr_pages - dbstart > 1 && !ra_has_index(ra, dbstart))
> +			page_cache_sync_readahead(dir->i_mapping, ra, f,
> +				dbstart, min(nr_pages - dbstart,
> +				(pgoff_t)MAX_DIR_RA_PAGES));
> +
>   		de = erofs_bread(&buf, dbstart, true);
>   		if (IS_ERR(de)) {
>   			erofs_err(sb, "failed to readdir of logical block %llu of nid %llu",
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index a32c03a80c70..ef9d1ee8c688 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -238,6 +238,9 @@ EROFS_FEATURE_FUNCS(xattr_filter, compat, COMPAT_XATTR_FILTER)
>   #define EROFS_I_BL_XATTR_BIT	(BITS_PER_LONG - 1)
>   #define EROFS_I_BL_Z_BIT	(BITS_PER_LONG - 2)
>   
> +/* maximum readahead pages of directory */
> +#define MAX_DIR_RA_PAGES	4

Could we set it as a per-sb sysfs configuration for users to config?

Thanks,
Gao Xiang