Re: [PATCH v8 6/9] erofs: introduce the page cache share feature

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

On 2025/11/14 17:55, Hongbo Li wrote:
> From: Hongzhen Luo <hongzhen@linux.alibaba.com>
> 
> Currently, reading files with different paths (or names) but the same
> content will consume multiple copies of the page cache, even if the
> content of these page caches is the same. For example, reading
> identical files (e.g., *.so files) from two different minor versions of
> container images will cost multiple copies of the same page cache,
> since different containers have different mount points. Therefore,
> sharing the page cache for files with the same content can save memory.
> 
> This introduces the page cache share feature in erofs. It allocate a
> deduplicated inode and use its page cache as shared. Reads for files
> with identical content will ultimately be routed to the page cache of
> the deduplicated inode. In this way, a single page cache satisfies
> multiple read requests for different files with the same contents.
> 
> Signed-off-by: Hongzhen Luo <hongzhen@linux.alibaba.com>
> Signed-off-by: Hongbo Li <lihongbo22@huawei.com>
> ---

...


> +
> +static int erofs_ishare_file_open(struct inode *inode, struct file *file)
> +{
> +	struct file *realfile;
> +	struct inode *dedup;
> +
> +	dedup = EROFS_I(inode)->ishare;
> +	if (!dedup)
> +		return -EINVAL;
> +
> +	realfile = alloc_file_pseudo(dedup, erofs_ishare_mnt, "erofs_ishare_file",
> +				     O_RDONLY, &erofs_file_fops);
> +	if (IS_ERR(realfile))
> +		return PTR_ERR(realfile);
> +
> +	file_ra_state_init(&realfile->f_ra, file->f_mapping);
> +	realfile->private_data = EROFS_I(inode);
> +	file->private_data = realfile;
> +	return 0;

Again, as Amir mentioned before, it should be converted to use (at least)
some of backing file interfaces, please see:
   file_user_path() and file_user_inode() in include/linux/fs.h

Or are you sure /proc/<pid>/maps is shown as expected?

Thanks,
Gao Xiang