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

[Chao Yu <chao@kernel.org>]

On 7/10/25 15:46, Gao Xiang wrote:
> 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?

Xiang,

Oh, that will be better, how about introducing new sysfs in separated patch?

Thanks,

> 
> Thanks,
> Gao Xiang