Re: [PATCH 2/2] fuse: Convert fuse_writepage_locked to take a folio

From: Matthew Wilcox <willy@infradead.org>
To: Bernd Schubert <bernd.schubert@fastmail.fm>
Cc: Miklos Szeredi <miklos@szeredi.hu>, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 2/2] fuse: Convert fuse_writepage_locked to take a folio
Date: Sat, 13 Apr 2024 16:59:44 +0100	[thread overview]
Message-ID: <Zhqr8Kj0rraBCJDY@casper.infradead.org> (raw)
In-Reply-To: <13cbb507-45b5-48fb-a696-cb43ad14a5b2@fastmail.fm>

On Sat, Apr 13, 2024 at 01:28:31PM +0200, Bernd Schubert wrote:
> On 2/28/24 19:29, Matthew Wilcox (Oracle) wrote:
> > The one remaining caller of fuse_writepage_locked() already has a folio,
> > so convert this function entirely.  Saves a few calls to compound_head()
> > but no attempt is made to support large folios in this patch.
>
> sorry for late review. The part I'm totally confused with (already
> without this patch), why is this handling a single page only and not the
> entire folio? Is it guaranteed that the folio has a single page only?

Hi Bernd,

, filesystems have to tell the VFS that they support large folios before
they'll see a large folio.  That's a call to mapping_set_large_folios()
today, although there's proposals to make that more granular.

If there's interest in supporting large folios in FUSE, I'm happy to
help, but my primary motivation is sorting out struct page, not fixing
individual filesystems.