linux-kernel - Re: [PATCH v3 5/6] netfs, 9p, afs, ceph: Use folios

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Date:   Wed, 03 Nov 2021 14:58:12 +0000
From:   David Howells <dhowells@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     dhowells@...hat.com, Jeff Layton <jlayton@...nel.org>,
        Marc Dionne <marc.dionne@...istor.com>,
        Ilya Dryomov <idryomov@...il.com>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        v9fs-developer@...ts.sourceforge.net,
        linux-afs@...ts.infradead.org, ceph-devel@...r.kernel.org,
        linux-cachefs@...hat.com, linux-fsdevel@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-cifs@...r.kernel.org,
        devel@...ts.orangefs.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 5/6] netfs, 9p, afs, ceph: Use folios

Matthew Wilcox <willy@...radead.org> wrote:

> > +	len = (size >= start + gran) ? gran : size - start;
> 
> This seems like the most complicated way to write this ... how about:
> 
>         size_t len = min_t(loff_t, isize - start, folio_size(folio));

I was trying to hedge against isize-start going negative.  Can this code race
against truncate?  truncate_setsize() changes i_size *before* invalidating the
pages.

> >  static int afs_symlink_readpage(struct file *file, struct page *page)
> >  {
> > -	struct afs_vnode *vnode = AFS_FS_I(page->mapping->host);
> > +	struct afs_vnode *vnode = AFS_FS_I(page_mapping(page)->host);
> 
> How does swap end up calling readpage on a symlink?

Um - readpage is called to read the symlink.

> > -	page_endio(page, false, ret);
> > +	page_endio(&folio->page, false, ret);
> 
> We need a folio_endio() ...

I think we mentioned this before and I think you said you had or would make a
patch for it.  I can just create a wrapper for it if that'll do.

David