linux-kernel - Re: [PATCH v12 07/10] erofs: introduce the page cache share feature

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Message-ID: <bb8e14f4-dbab-4974-a180-b436a00625d1@huawei.com>
Date: Thu, 8 Jan 2026 20:20:08 +0800
From: Hongbo Li <lihongbo22@...wei.com>
To: Gao Xiang <hsiangkao@...ux.alibaba.com>
CC: <djwong@...nel.org>, <amir73il@...il.com>, <hch@....de>,
	<linux-fsdevel@...r.kernel.org>, <linux-erofs@...ts.ozlabs.org>,
	<linux-kernel@...r.kernel.org>, Chao Yu <chao@...nel.org>,
	<brauner@...nel.org>
Subject: Re: [PATCH v12 07/10] erofs: introduce the page cache share feature

Hi, Xiang

On 2026/1/7 14:08, Gao Xiang wrote:
> 
> 
> On 2025/12/31 17:01, Hongbo Li wrote:

...

>> +
>> +static int erofs_ishare_file_release(struct inode *inode, struct file 
>> *file)
>> +{
>> +    struct file *realfile = file->private_data;
>> +
>> +    iput(realfile->f_inode);
>> +    fput(realfile);
>> +    file->private_data = NULL;
>> +    return 0;
>> +}
>> +
>> +static ssize_t erofs_ishare_file_read_iter(struct kiocb *iocb,
>> +                       struct iov_iter *to)
>> +{
>> +    struct file *realfile = iocb->ki_filp->private_data;
>> +    struct kiocb dedup_iocb;
>> +    ssize_t nread;
>> +
>> +    if (!iov_iter_count(to))
>> +        return 0;
>> +
>> +    /* fallback to the original file in DIRECT mode */
>> +    if (iocb->ki_flags & IOCB_DIRECT)
>> +        realfile = iocb->ki_filp;
>> +
>> +    kiocb_clone(&dedup_iocb, iocb, realfile);
>> +    nread = filemap_read(&dedup_iocb, to, 0);
>> +    iocb->ki_pos = dedup_iocb.ki_pos;
> 
> I think it will not work for the AIO cases.
> 
> In order to make it simplified, how about just
> allowing sync and non-direct I/O first, and
> defering DIO/AIO support later?
> 

Ok, but what about doing the fallback logic:

1. For direct io: fallback to the original file.
2. For AIO: initialize the sync io by init_sync_kiocb (May be we can 
just replace kiocb_clone with init_sync_kiocb).

Thanks,
Hongbo

>> +    file_accessed(iocb->ki_filp);
> 
> I don't think it's useful in practice.
> 

Just keep in consistent with filemap_read?

> 
>> +    return nread;
>> +}
>> +
>> +static int erofs_ishare_mmap(struct file *file, struct vm_area_struct 
>> *vma)
>> +{
>> +    struct file *realfile = file->private_data;
>> +
>> +    vma_set_file(vma, realfile);
>> +    return generic_file_readonly_mmap(file, vma);
>> +}
>> +

...

>> @@ -649,6 +659,16 @@ static int erofs_fc_fill_super(struct super_block 
>> *sb, struct fs_context *fc)
>>       sb->s_maxbytes = MAX_LFS_FILESIZE;
>>       sb->s_op = &erofs_sops;
>> +    if (sbi->domain_id &&
>> +        (!sbi->fsid && !test_opt(&sbi->opt, INODE_SHARE))) {
>> +        errorfc(fc, "domain_id should be with fsid or inode_share 
>> option");
>> +        return -EINVAL;
>> +    }
> 
> Is that really needed?
> 

Ok, I will remove it in next version.

Thanks,
Hongbo

> 
> 
>> +    if (test_opt(&sbi->opt, DAX_ALWAYS) && test_opt(&sbi->opt, 
>> INODE_SHARE)) {
>> +        errorfc(fc, "dax is not allowed when inode_share is on");
> 
>          errorfc(fc, "FSDAX is not allowed when inode_share is on");
> 
> Thanks,
> Gao Xiang