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

[Hongbo Li]

On 2026/1/22 22:01, Gao Xiang wrote:
> 
> 
> 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?

I am very sorry for making such stupid mistake. :(

Thanks,
Hongbo

> 
> Thanks,
> Gao Xiang