Re: [PATCH] erofs: use the shared page cache for splice in inode_share mode

[Jingbo Xu <jefflexu@linux.alibaba.com>]

On 8/20/26 8:37 PM, Zhan Xusheng wrote:
> On Thu, 20 Aug 2026 17:53:20 +0800, Jingbo Xu wrote:
>> Please refer to backing_file_splice_read() called from
>> ovl_splice_read(), file_accessed() needs to be called on the original
>> file (just as what .read_iter() i.e. filemap_read() does), and the input
>> @ppos needs to be updated accordingly.
> 
> Taking the file_accessed() one, thanks.  filemap_splice_read() calls it at
> mm/filemap.c:3155 on whatever file it was handed, so on the backing file,
> whereas backing_file_splice_read() ends in ctx->accessed(iocb->ki_filp),
> which for ovl_splice_read() is the original.  v2 adds file_accessed(in).
> 
> @ppos looks already handled to me.  filemap_splice_read() takes a loff_t *
> and advances it itself, at mm/filemap.c:3144; its internal kiocb is seeded
> from *ppos at 3083 and 3098, not the other way round.  ovl_splice_read()
> has to copy iocb.ki_pos back because backing_file_splice_read() takes a
> struct kiocb and hands &iocb->ki_pos to vfs_splice_read().  Say if I have
> that wrong.

Make sense.


> 
> One you may want for read_iter too: it clones the kiocb onto the backing
> file, so filemap_read() marks that one accessed rather than the user's
> file, which is the shape splice_read had.  Neither is observable today,
> since erofs_fc_fill_super() sets SB_RDONLY | SB_NOATIME and the backing
> file is opened O_NOATIME, so both reach a no-op.  That is why I left
> read_iter alone here.

Okay, it seems that file_accessed() shall also be added to
erofs_ishare_file_read_iter()?


-- 
Thanks,
Jingbo