linux-kernel - Re: [PATCH v4] erofs: support to readahead dirent blocks in erofs

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Message-ID: <e2aeb886-cb45-4f75-aaf9-7f0855b3a87a@kernel.org>
Date: Mon, 21 Jul 2025 11:16:16 +0800
From: Chao Yu <chao@...nel.org>
To: Gao Xiang <hsiangkao@...ux.alibaba.com>, xiang@...nel.org
Cc: chao@...nel.org, linux-erofs@...ts.ozlabs.org,
 linux-kernel@...r.kernel.org, Yue Hu <zbestahu@...il.com>,
 Jeffle Xu <jefflexu@...ux.alibaba.com>, Sandeep Dhavale
 <dhavale@...gle.com>, Hongbo Li <lihongbo22@...wei.com>
Subject: Re: [PATCH v4] erofs: support to readahead dirent blocks in
 erofs_readdir()

On 7/21/25 10:24, Gao Xiang wrote:
> 
> 
> On 2025/7/21 10:13, Chao Yu wrote:
>> This patch supports to readahead more blocks in erofs_readdir(), it can
>> enhance readdir performance in large direcotry.
>>
>> readdir test in a large directory which contains 12000 sub-files.
>>
>>         files_per_second
>> Before:        926385.54
>> After:        2380435.562
>>
>> Meanwhile, let's introduces a new sysfs entry to control readahead
>> bytes to provide more flexible policy for readahead of readdir().
>> - location: /sys/fs/erofs/<disk>/dir_ra_bytes
>> - default value: 16384
>> - disable readahead: set the value to 0
>>
>> Signed-off-by: Chao Yu <chao@...nel.org>
>> ---
>> v4:
>> - clean up codes and comments
>>   Documentation/ABI/testing/sysfs-fs-erofs |  8 ++++++++
>>   fs/erofs/dir.c                           | 14 ++++++++++++++
>>   fs/erofs/internal.h                      |  4 ++++
>>   fs/erofs/super.c                         |  2 ++
>>   fs/erofs/sysfs.c                         |  2 ++
>>   5 files changed, 30 insertions(+)
>>
>> diff --git a/Documentation/ABI/testing/sysfs-fs-erofs b/Documentation/ABI/testing/sysfs-fs-erofs
>> index bf3b6299c15e..85fa56ca092c 100644
>> --- a/Documentation/ABI/testing/sysfs-fs-erofs
>> +++ b/Documentation/ABI/testing/sysfs-fs-erofs
>> @@ -35,3 +35,11 @@ Description:    Used to set or show hardware accelerators in effect
>>           and multiple accelerators are separated by '\n'.
>>           Supported accelerator(s): qat_deflate.
>>           Disable all accelerators with an empty string (echo > accel).
>> +
>> +What:        /sys/fs/erofs/<disk>/dir_ra_bytes
>> +Date:        July 2025
>> +Contact:    "Chao Yu" <chao@...nel.org>
>> +Description:    Used to set or show readahead bytes during readdir(), by
>> +        default the value is 16384.
>> +
>> +        - 0: disable readahead.
>> diff --git a/fs/erofs/dir.c b/fs/erofs/dir.c
>> index 3e4b38bec0aa..99745c272b60 100644
>> --- a/fs/erofs/dir.c
>> +++ b/fs/erofs/dir.c
>> @@ -47,8 +47,12 @@ 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);
>> +    pgoff_t ra_pages = DIV_ROUND_UP_POW2(
>> +            EROFS_I_SB(dir)->dir_ra_bytes, PAGE_SIZE);
>> +    pgoff_t nr_pages = DIV_ROUND_UP_POW2(dir->i_size, PAGE_SIZE);
>>       int err = 0;
>>       bool initial = true;
>>   @@ -63,6 +67,16 @@ static int erofs_readdir(struct file *f, struct dir_context *ctx)
>>               break;
>>           }
>>   +        /* readahead blocks to enhance performance in large directory */
>> +        if (ra_pages) {
>> +            pgoff_t idx = DIV_ROUND_UP(ctx->pos, PAGE_SIZE);
> 
> Can we use DIV_ROUND_UP_POW2 here too? If it's okay,
> I will update the patch manually when applied.

Xiang,

Yeah, looks fine to me.

Please go ahead to update it while applying, thanks for your help. :)

Thanks,

> 
> Otherwise it looks good to me,
> Reviewed-by: Gao Xiang <hsiangkao@...ux.alibaba.com>
> 
> Thanks,
> Gao Xiang