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From: Matthew Wilcox <willy@infradead.org>
To: David Howells <dhowells@redhat.com>
Cc: Trond Myklebust <trondmy@hammerspace.com>,
	Anna Schumaker <anna.schumaker@netapp.com>,
	Steve French <sfrench@samba.org>,
	Jeff Layton <jlayton@redhat.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-afs@lists.infradead.org, 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 54/61] afs: Wait on PG_fscache before modifying/releasing a page
Date: Wed, 6 May 2020 04:09:42 -0700	[thread overview]
Message-ID: <20200506110942.GL16070@bombadil.infradead.org> (raw)
In-Reply-To: <683739.1588751878@warthog.procyon.org.uk>

On Wed, May 06, 2020 at 08:57:58AM +0100, David Howells wrote:
> Matthew Wilcox <willy@infradead.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?

Can you remind me why ITER_MAPPING needs:

"The caller must guarantee that the pages are all present and they must be
locked using PG_locked, PG_writeback or PG_fscache to prevent them from
going away or being migrated whilst they're being accessed."

An elevated refcount prevents migration, and it also prevents the pages
from being freed.  It doesn't prevent them from being truncated out of
the file, but it does ensure the pages aren't reallocated.

  reply	other threads:[~2020-05-06 11:10 UTC|newest]

Thread overview: 92+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-04 17:07 [RFC PATCH 00/61] fscache, cachefiles: Rewrite the I/O interface in terms of kiocb/iov_iter David Howells
2020-05-04 17:07 ` David Howells
2020-05-04 17:07 ` [RFC PATCH 01/61] afs: Make afs_zap_data() static David Howells
2020-05-04 17:07 ` [RFC PATCH 02/61] iov_iter: Add ITER_MAPPING David Howells
2020-05-04 17:07   ` David Howells
2020-05-04 17:07 ` [RFC PATCH 03/61] vm: Add wait/unlock functions for PG_fscache David Howells
2020-05-04 17:08 ` [RFC PATCH 04/61] vfs: Export rw_verify_area() for use by cachefiles David Howells
2020-05-04 17:08 ` [RFC PATCH 05/61] vfs: Provide S_CACHE_FILE inode flag David Howells
2020-05-04 17:08   ` David Howells
2020-05-04 17:08 ` [RFC PATCH 06/61] afs: Disable use of the fscache I/O routines David Howells
2020-05-04 17:08 ` [RFC PATCH 07/61] fscache: Add a cookie debug ID and use that in traces David Howells
2020-05-04 17:08 ` [RFC PATCH 08/61] fscache: Procfile to display cookies David Howells
2020-05-04 17:08 ` [RFC PATCH 09/61] fscache: Temporarily disable network filesystems' use of fscache David Howells
2020-05-04 17:08 ` [RFC PATCH 10/61] fscache: Remove the old I/O API David Howells
2020-05-04 17:08   ` David Howells
2020-05-04 17:09 ` [RFC PATCH 11/61] fscache: Remove the netfs data from the cookie David Howells
2020-05-04 17:09 ` [RFC PATCH 12/61] fscache: Remove struct fscache_cookie_def David Howells
2020-05-04 17:09   ` David Howells
2020-05-04 17:09 ` [RFC PATCH 13/61] fscache: Remove store_limit* from struct fscache_object David Howells
2020-05-04 17:09 ` [RFC PATCH 14/61] fscache: Remove fscache_check_consistency() David Howells
2020-05-04 17:09   ` David Howells
2020-05-04 17:09 ` [RFC PATCH 15/61] fscache: Remove fscache_attr_changed() David Howells
2020-05-04 17:09 ` [RFC PATCH 16/61] fscache: Remove obsolete stats David Howells
2020-05-04 17:09   ` David Howells
2020-05-04 17:10 ` [RFC PATCH 17/61] fscache: Remove old I/O tracepoints David Howells
2020-05-04 17:10 ` [RFC PATCH 18/61] fscache: Temporarily disable fscache_invalidate() David Howells
2020-05-04 17:10 ` [RFC PATCH 19/61] fscache: Remove the I/O operation manager David Howells
2020-05-04 17:10   ` David Howells
2020-05-04 17:10 ` [RFC PATCH 20/61] cachefiles: Remove tree of active files and use S_CACHE_FILE inode flag David Howells
2020-05-04 17:10   ` David Howells
2020-05-04 17:10 ` [RFC PATCH 21/61] fscache: Provide a simple thread pool for running ops asynchronously David Howells
2020-05-04 17:10   ` David Howells
2020-05-04 17:10 ` [RFC PATCH 22/61] fscache: Replace the object management state machine David Howells
2020-05-04 17:10 ` [RFC PATCH 23/61] fscache: Rewrite the I/O API based on iov_iter David Howells
2020-05-04 17:11 ` [RFC PATCH 24/61] fscache: Remove fscache_wait_on_invalidate() David Howells
2020-05-04 17:11   ` David Howells
2020-05-04 17:11 ` [RFC PATCH 25/61] fscache: Keep track of size of a file last set independently on the server David Howells
2020-05-04 17:11 ` [RFC PATCH 26/61] fscache, cachefiles: Fix disabled histogram warnings David Howells
2020-05-04 17:11 ` [RFC PATCH 27/61] fscache: Recast assertion in terms of cookie not being an index David Howells
2020-05-04 17:11 ` [RFC PATCH 28/61] cachefiles: Remove some redundant checks on unsigned values David Howells
2020-05-04 17:11 ` [RFC PATCH 29/61] cachefiles: trace: Log coherency checks David Howells
2020-05-04 17:12 ` [RFC PATCH 30/61] cachefiles: Split cachefiles_drop_object() up a bit David Howells
2020-05-04 17:12   ` David Howells
2020-05-04 17:12 ` [RFC PATCH 31/61] cachefiles: Implement new fscache I/O backend API David Howells
2020-05-04 17:12 ` [RFC PATCH 32/61] cachefiles: Merge object->backer into object->dentry David Howells
2020-05-04 17:12   ` David Howells
2020-05-04 17:12 ` [RFC PATCH 33/61] cachefiles: Implement a content-present indicator and bitmap David Howells
2020-05-04 17:12 ` [RFC PATCH 34/61] cachefiles: Implement extent shaper David Howells
2020-05-04 17:12 ` [RFC PATCH 35/61] cachefiles: Round the cachefile size up to DIO block size David Howells
2020-05-04 17:12 ` [RFC PATCH 36/61] cachefiles: Implement read and write parts of new I/O API David Howells
2020-05-04 17:13 ` [RFC PATCH 37/61] cachefiles: Add I/O tracepoints David Howells
2020-05-04 17:13 ` [RFC PATCH 38/61] fscache: Add read helper David Howells
2020-05-04 17:13   ` David Howells
2020-05-04 17:13 ` [RFC PATCH 39/61] fscache: Display cache-specific data in /proc/fs/fscache/objects David Howells
2020-05-04 17:13   ` David Howells
2020-05-04 17:13 ` [RFC PATCH 40/61] fscache: Remove more obsolete stats David Howells
2020-05-04 17:13 ` [RFC PATCH 41/61] fscache: New stats David Howells
2020-05-04 17:13 ` [RFC PATCH 42/61] fscache, cachefiles: Rewrite invalidation David Howells
2020-05-04 17:13 ` [RFC PATCH 43/61] fscache: Implement "will_modify" parameter on fscache_use_cookie() David Howells
2020-05-04 17:14 ` [RFC PATCH 44/61] fscache: Provide resize operation David Howells
2020-05-04 17:14   ` David Howells
2020-05-04 17:14 ` [RFC PATCH 45/61] fscache: Remove the update operation David Howells
2020-05-04 17:14   ` David Howells
2020-05-04 17:14 ` [RFC PATCH 46/61] cachefiles: Shape write requests David Howells
2020-05-04 17:14 ` [RFC PATCH 47/61] afs: Remove afs_zero_fid as it's not used David Howells
2020-05-04 17:14 ` [RFC PATCH 48/61] afs: Move key to afs_read struct David Howells
2020-05-04 17:14   ` David Howells
2020-05-04 17:14 ` [RFC PATCH 49/61] afs: Don't truncate iter during data fetch David Howells
2020-05-04 17:15 ` [RFC PATCH 50/61] afs: Set up the iov_iter before calling afs_extract_data() David Howells
2020-05-04 17:15   ` David Howells
2020-05-04 17:15 ` [RFC PATCH 51/61] afs: Use ITER_MAPPING for writing David Howells
2020-05-04 17:15 ` [RFC PATCH 52/61] afs: Interpose struct fscache_io_request into struct afs_read David Howells
2020-05-04 17:15   ` David Howells
2020-05-04 17:15 ` [RFC PATCH 53/61] afs: Note the amount transferred in fetch-data delivery David Howells
2020-05-04 17:15 ` [RFC PATCH 54/61] afs: Wait on PG_fscache before modifying/releasing a page David Howells
2020-05-05 11:59   ` Matthew Wilcox
2020-05-06  7:57   ` David Howells
2020-05-06 11:09     ` Matthew Wilcox [this message]
2020-05-06 14:24     ` David Howells
2020-05-08 14:39     ` David Howells
2020-05-08 14:39       ` David Howells
2020-05-04 17:15 ` [RFC PATCH 55/61] afs: Use new fscache I/O API David Howells
2020-05-04 17:15 ` [RFC PATCH 56/61] afs: Copy local writes to the cache when writing to the server David Howells
2020-05-04 17:16 ` [RFC PATCH 57/61] afs: Invoke fscache_resize_cookie() when handling ATTR_SIZE for setattr David Howells
2020-05-04 17:16 ` [RFC PATCH 58/61] fscache: Rewrite the main document David Howells
2020-05-04 17:16 ` [RFC PATCH 59/61] fscache: Remove the obsolete API bits from the documentation David Howells
2020-05-04 17:16 ` [RFC PATCH 60/61] fscache: Document the new netfs API David Howells
2020-05-04 17:16 ` [RFC PATCH 61/61] fscache: Document the rewritten cache backend API David Howells
2020-05-04 17:54 ` [RFC PATCH 00/61] fscache, cachefiles: Rewrite the I/O interface in terms of kiocb/iov_iter Jeff Layton
2020-05-04 17:54   ` Jeff Layton
2020-05-05  6:05 ` Christoph Hellwig
2020-05-05  6:05   ` Christoph Hellwig

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