[PATCH v16 06/10] erofs: introduce the page cache share feature

[Gao Xiang]

On 2026/1/22 21:37, Hongbo Li wrote:
> From: Hongzhen Luo <hongzhen at 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
> shared inode and use its page cache as shared. Reads for files
> with identical content will ultimately be routed to the page cache of
> the shared inode. In this way, a single page cache satisfies
> multiple read requests for different files with the same contents.
> 
> We introduce new mount option `inode_share` to enable the page
> sharing mode during mounting. This option is used in conjunction
> with `domain_id` to share the page cache within the same trusted
> domain.
> 
> Signed-off-by: Hongzhen Luo <hongzhen at linux.alibaba.com>
> Signed-off-by: Hongbo Li <lihongbo22 at huawei.com>
> ---
>   Documentation/filesystems/erofs.rst |   5 +
>   fs/erofs/Makefile                   |   1 +
>   fs/erofs/inode.c                    |   1 -
>   fs/erofs/internal.h                 |  31 ++++++
>   fs/erofs/ishare.c                   | 167 ++++++++++++++++++++++++++++
>   fs/erofs/super.c                    |  62 ++++++++++-
>   fs/erofs/xattr.c                    |  34 ++++++
>   fs/erofs/xattr.h                    |   3 +
>   8 files changed, 301 insertions(+), 3 deletions(-)
>   create mode 100644 fs/erofs/ishare.c
> 
> diff --git a/Documentation/filesystems/erofs.rst b/Documentation/filesystems/erofs.rst
> index 40dbf3b6a35f..bfef8e87f299 100644
> --- a/Documentation/filesystems/erofs.rst
> +++ b/Documentation/filesystems/erofs.rst
> @@ -129,7 +129,12 @@ fsid=%s                Specify a filesystem image ID for Fscache back-end.
>   domain_id=%s           Specify a trusted domain ID for fscache mode so that
>                          different images with the same blobs, identified by blob IDs,
>                          can share storage within the same trusted domain.
> +                       Also used for different filesystems with inode page sharing
> +                       enabled to share page cache within the trusted domain.
>   fsoffset=%llu          Specify block-aligned filesystem offset for the primary device.
> +inode_share            Enable inode page sharing for this filesystem.  Inodes with
> +                       identical content within the same domain ID can share the
> +                       page cache.
>   ===================    =========================================================
>   
>   Sysfs Entries
> diff --git a/fs/erofs/Makefile b/fs/erofs/Makefile
> index 549abc424763..a80e1762b607 100644
> --- a/fs/erofs/Makefile
> +++ b/fs/erofs/Makefile
> @@ -10,3 +10,4 @@ erofs-$(CONFIG_EROFS_FS_ZIP_ZSTD) += decompressor_zstd.o
>   erofs-$(CONFIG_EROFS_FS_ZIP_ACCEL) += decompressor_crypto.o
>   erofs-$(CONFIG_EROFS_FS_BACKED_BY_FILE) += fileio.o
>   erofs-$(CONFIG_EROFS_FS_ONDEMAND) += fscache.o
> +erofs-$(CONFIG_EROFS_FS_PAGE_CACHE_SHARE) += ishare.o
> diff --git a/fs/erofs/inode.c b/fs/erofs/inode.c
> index 389632bb46c4..202cbbb4eada 100644
> --- a/fs/erofs/inode.c
> +++ b/fs/erofs/inode.c
> @@ -203,7 +203,6 @@ static int erofs_read_inode(struct inode *inode)
>   
>   static int erofs_fill_inode(struct inode *inode)
>   {
> -	struct erofs_inode *vi = EROFS_I(inode);

Why this line is in this patch other than
"erofs: add erofs_inode_set_aops helper to set the aops[.]"

And there is an unneeded dot at the end of the subject.

Could you check the patches carefully before sending
out the next version?

Thanks,
Gao Xiang