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From: "J. Bruce Fields" <bfields@fieldses.org>
To: David Howells <dhowells@redhat.com>
Cc: Amir Goldstein <amir73il@gmail.com>,
	linux-cachefs@redhat.com, Jeff Layton <jlayton@redhat.com>,
	David Wysochanski <dwysocha@redhat.com>,
	"Matthew Wilcox (Oracle)" <willy@infradead.org>,
	Christoph Hellwig <hch@infradead.org>,
	Dave Chinner <dchinner@redhat.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-afs@lists.infradead.org,
	Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
	CIFS <linux-cifs@vger.kernel.org>,
	ceph-devel <ceph-devel@vger.kernel.org>,
	v9fs-developer@lists.sourceforge.net,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Miklos Szeredi <miklos@szeredi.hu>
Subject: Re: fscache: Redesigning the on-disk cache
Date: Mon, 8 Mar 2021 13:54:10 -0500	[thread overview]
Message-ID: <20210308185410.GE7284@fieldses.org> (raw)
In-Reply-To: <517184.1615194835@warthog.procyon.org.uk>

On Mon, Mar 08, 2021 at 09:13:55AM +0000, David Howells wrote:
> Amir Goldstein <amir73il@gmail.com> wrote:
> > With ->fiemap() you can at least make the distinction between a non existing
> > and an UNWRITTEN extent.
> 
> I can't use that for XFS, Ext4 or btrfs, I suspect.  Christoph and Dave's
> assertion is that the cache can't rely on the backing filesystem's metadata
> because these can arbitrarily insert or remove blocks of zeros to bridge or
> split extents.

Could you instead make some sort of explicit contract with the
filesystem?  Maybe you'd flag it at mkfs time and query for it before
allowing a filesystem to be used for fscache.  You don't need every
filesystem to support fscache, right, just one acceptable one?

--b.

  parent reply	other threads:[~2021-03-08 18:55 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-03 23:20 David Howells
2021-03-04 13:47 ` fscache: Redesigning the on-disk cache - LRU handling David Howells
2021-03-05  9:46 ` fscache: Redesigning the on-disk cache Amir Goldstein
2021-03-08  9:13 ` David Howells
2021-03-08 10:35   ` Amir Goldstein
2021-03-08 11:28   ` Metadata writtenback notification? -- was " David Howells
2021-03-08 22:32     ` Dave Chinner
2021-03-08 23:20       ` Matthew Wilcox
2021-03-09 11:27     ` David Howells
2021-03-08 18:54   ` J. Bruce Fields [this message]
2021-03-08 19:08   ` David Howells
2021-03-08 21:55   ` Dave Chinner
2021-03-09  9:21   ` David Howells

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