linux-kernel - Re: [RFC PATCH 0/3] 9p: Further netfslib-related changes

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Date: Mon, 29 Jan 2024 15:14:28 +0100
From: Christian Schoenebeck <linux_oss@...debyte.com>
To: Eric Van Hensbergen <ericvh@...nel.org>,
 Dominique Martinet <asmadeus@...ewreck.org>,
 Latchesar Ionkov <lucho@...kov.net>, David Howells <dhowells@...hat.com>,
 Matthew Wilcox <willy@...radead.org>
Cc: Jeff Layton <jlayton@...nel.org>,
 Christian Brauner <christian@...uner.io>, netfs@...ts.linux.dev,
 v9fs@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/3] 9p: Further netfslib-related changes

On Monday, January 29, 2024 12:54:34 PM CET David Howells wrote:
> Hi Eric, Dominique,
> 
> Here are some netfslib-related changes we might want to consider applying
> to 9p:
> 
>  (1) Enable large folio support for 9p.  This is handled entirely by
>      netfslib and is already supported in afs.  I wonder if we should limit
>      the maximum folio size to 1MiB to match the maximum I/O size in the 9p
>      protocol.

The limit depends on user's 'msize' 9p client option and on the 9p transport
implementation. The hard limit with virtio transport for instance is currently
just 500k (patches for virtio 4MB limit fetching dust unfortunately).

Would you see an advantage to limit folio size? I mean p9_client_read() etc.
are automatically limiting the read/write chunk size accordingly.

>  (2) Make better use of netfslib's writethrough caching support by not
>      disabling caching for O_DSYNC.  netfs_perform_write() will set up
>      and dispatch write requests as it copies data into the pagecache.
> 
>  (3) Always update netfs_inode::remote_size to reflect what we think the
>      server's idea of the file size is.  This is separate from
>      inode::i_size which is our idea of what it should be if all of our
>      outstanding dirty data is committed.
> 
> The patches can also be found here:
> 
> 	https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=netfs-9p
> 
> Thanks,
> David
> 
> David Howells (2):
>   9p: Make better use of netfslib's writethrough caching
>   9p: Always update remote_i_size in stat2inode
> 
> Dominique Martinet (1):
>   9p: Enable large folio support
> 
>  fs/9p/fid.h            | 3 +--
>  fs/9p/vfs_inode.c      | 1 +
>  fs/9p/vfs_inode_dotl.c | 6 +++---
>  3 files changed, 5 insertions(+), 5 deletions(-)