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From: "J. Bruce Fields" <bfields@fieldses.org>
To: David Howells <dhowells@redhat.com>
Cc: Trond Myklebust <trondmy@hammerspace.com>,
	Anna Schumaker <anna.schumaker@netapp.com>,
	Steve French <sfrench@samba.org>,
	Dominique Martinet <asmadeus@codewreck.org>,
	Takashi Iwai <tiwai@suse.de>,
	Matthew Wilcox <willy@infradead.org>,
	linux-afs@lists.infradead.org, Jeff Layton <jlayton@redhat.com>,
	David Wysochanski <dwysocha@redhat.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-cachefs@redhat.com, linux-nfs@vger.kernel.org,
	linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org,
	v9fs-developer@lists.sourceforge.net,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH 00/25] Network fs helper library & fscache kiocb API
Date: Thu, 21 Jan 2021 14:09:37 -0500	[thread overview]
Message-ID: <20210121190937.GE20964@fieldses.org> (raw)
In-Reply-To: <1851804.1611255313@warthog.procyon.org.uk>

On Thu, Jan 21, 2021 at 06:55:13PM +0000, David Howells wrote:
> J. Bruce Fields <bfields@fieldses.org> wrote:
> 
> > > Fixing this requires a much bigger overhaul of cachefiles than this patchset
> > > performs.
> > 
> > That sounds like "sometimes you may get file corruption and there's
> > nothing you can do about it".  But I know people actually use fscache,
> > so it must be reliable at least for some use cases.
> 
> Yes.  That's true for the upstream code because that uses bmap.

Sorry, when you say "that's true", what part are you referring to?

> I'm switching
> to use SEEK_HOLE/SEEK_DATA to get rid of the bmap usage, but it doesn't change
> the issue.
> 
> > Is it that those "bridging" blocks only show up in certain corner cases
> > that users can arrange to avoid?  Or that it's OK as long as you use
> > certain specific file systems whose behavior goes beyond what's
> > technically required by the bamp or seek interfaces?
> 
> That's a question for the xfs, ext4 and btrfs maintainers, and may vary
> between kernel versions and fsck or filesystem packing utility versions.

So, I'm still confused: there must be some case where we know fscache
actually works reliably and doesn't corrupt your data, right?

--b.

  reply	other threads:[~2021-01-21 19:16 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-20 22:21 [RFC][PATCH 00/25] Network fs helper library & fscache kiocb API David Howells
2021-01-20 22:21 ` [PATCH 01/25] iov_iter: Add ITER_XARRAY David Howells
2021-01-21 13:34   ` Matthew Wilcox
2021-01-21 14:54   ` David Howells
2021-01-20 22:21 ` [PATCH 02/25] vm: Add wait/unlock functions for PG_fscache David Howells
2021-01-20 22:21 ` [PATCH 03/25] mm: Implement readahead_control pageset expansion David Howells
2021-01-20 22:22 ` [PATCH 04/25] vfs: Export rw_verify_area() for use by cachefiles David Howells
2021-01-20 22:22 ` [PATCH 05/25] cachefiles: Drop superfluous readpages aops NULL check David Howells
2021-01-20 22:22 ` [PATCH 06/25] netfs: Make a netfs helper module David Howells
2021-01-20 22:22 ` [PATCH 07/25] netfs: Provide readahead and readpage netfs helpers David Howells
2021-01-20 22:23 ` [PATCH 08/25] netfs: Add tracepoints David Howells
2021-01-20 22:23 ` [PATCH 09/25] netfs: Gather stats David Howells
2021-01-20 22:23 ` [PATCH 10/25] netfs: Add write_begin helper David Howells
2021-01-20 22:23 ` [PATCH 11/25] netfs: Define an interface to talk to a cache David Howells
2021-01-20 22:23 ` [PATCH 12/25] fscache, cachefiles: Add alternate API to use kiocb for read/write to cache David Howells
2021-01-20 22:23 ` [PATCH 13/25] afs: Disable use of the fscache I/O routines David Howells
2021-01-20 22:24 ` [PATCH 14/25] afs: Pass page into dirty region helpers to provide THP size David Howells
2021-01-20 22:24 ` [PATCH 15/25] afs: Print the operation debug_id when logging an unexpected data version David Howells
2021-01-20 22:24 ` [PATCH 16/25] afs: Move key to afs_read struct David Howells
2021-01-20 22:24 ` [PATCH 17/25] afs: Don't truncate iter during data fetch David Howells
2021-01-20 22:24 ` [PATCH 18/25] afs: Log remote unmarshalling errors David Howells
2021-01-20 22:25 ` [PATCH 19/25] afs: Set up the iov_iter before calling afs_extract_data() David Howells
2021-01-20 22:25 ` [PATCH 20/25] afs: Use ITER_XARRAY for writing David Howells
2021-01-20 22:25 ` [PATCH 21/25] afs: Wait on PG_fscache before modifying/releasing a page David Howells
2021-01-20 22:25 ` [PATCH 22/25] afs: Extract writeback extension into its own function David Howells
2021-01-20 22:25 ` [PATCH 23/25] afs: Prepare for use of THPs David Howells
2021-01-20 22:26 ` [PATCH 24/25] afs: Use the fs operation ops to handle FetchData completion David Howells
2021-01-20 22:26 ` [PATCH 25/25] afs: Use new fscache read helper API David Howells
2021-01-21 16:46 ` [RFC][PATCH 00/25] Network fs helper library & fscache kiocb API J. Bruce Fields
2021-01-21 17:02 ` David Howells
2021-01-21 17:43   ` J. Bruce Fields
2021-01-21 18:55   ` David Howells
2021-01-21 19:09     ` J. Bruce Fields [this message]
2021-01-21 20:08     ` David Howells
2021-01-22 16:01       ` J. Bruce Fields
2021-01-22 16:06       ` David Howells
2021-01-22  8:23     ` Christoph Hellwig

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