linux-kernel - Re: [RFC PATCH 54/61] afs: Wait on PG_fscache before modifying/releasing a page

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Message-ID: <683739.1588751878@warthog.procyon.org.uk>
Date:   Wed, 06 May 2020 08:57:58 +0100
From:   David Howells <dhowells@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     dhowells@...hat.com, Trond Myklebust <trondmy@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve French <sfrench@...ba.org>,
        Jeff Layton <jlayton@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-afs@...ts.infradead.org, linux-nfs@...r.kernel.org,
        linux-cifs@...r.kernel.org, ceph-devel@...r.kernel.org,
        v9fs-developer@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 54/61] afs: Wait on PG_fscache before modifying/releasing a page

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

> > PG_fscache is going to be used to indicate that a page is being written to
> > the cache, and that the page should not be modified or released until it's
> > finished.
> > 
> > Make afs_invalidatepage() and afs_releasepage() wait for it.
> 
> Well, why?  Keeping a refcount on the page will prevent it from going
> away while it's being written to storage.  And the fact that it's
> being written to this cache is no reason to delay the truncate of a file
> (is it?)

Won't that screw up ITER_MAPPING?  Does that mean that ITER_MAPPING isn't
viable?

David