From: Al Viro <viro@zeniv.linux.org.uk>
To: David Howells <dhowells@redhat.com>
Cc: linux-cachefs@redhat.com, linux-afs@lists.infradead.org,
"Matthew Wilcox (Oracle)" <willy@infradead.org>,
ceph-devel@vger.kernel.org, Jeff Layton <jlayton@kernel.org>,
Andrew W Elble <aweits@rit.edu>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 0/3] netfs, afs: Fix netfs_write_begin and THP handling
Date: Fri, 18 Jun 2021 03:46:24 +0000 [thread overview]
Message-ID: <YMwXEAMxEgGADeiG@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <162391823192.1173366.9740514875196345746.stgit@warthog.procyon.org.uk>
On Thu, Jun 17, 2021 at 09:23:51AM +0100, David Howells wrote:
>
> Here are some patches to fix netfs_write_begin() and the handling of THPs in
> that and afs_write_begin/end() in the following ways:
>
> (1) Use offset_in_thp() rather than manually calculating the offset into
> the page.
>
> (2) In the future, the len parameter may extend beyond the page allocated.
> This is because the page allocation is deferred to write_begin() and
> that gets to decide what size of THP to allocate.
>
> (3) In netfs_write_begin(), extract the decision about whether to skip a
> page out to its own helper and have that clear around the region to be
> written, but not clear that region. This requires the filesystem to
> patch it up afterwards if the hole doesn't get completely filled.
>
> (4) Due to (3), afs_write_end() now needs to handle short data write into
> the page by generic_perform_write(). I've adopted an analogous
> approach to ceph of just returning 0 in this case and letting the
> caller go round again.
Series looks sane. I'd like to hear about the thp-related plans in
more detail, but that's a separate story.
> I wonder if generic_perform_write() should pass in a flag indicating
> whether this is the first attempt or a second attempt at this, and on the
> second attempt we just completely prefill the page and just let the partial
> write stand - which we have to do if the page was already uptodate when we
> started.
Not really - we'll simply get a shorter chunk next time around (with
the patches in -next right now it'll be "the amount we'd actually
managed to copy this time around" in case ->write_begin() tells us
to take a hike), and that shorter chunk is what ->write_begin() will
see. No need for the flags...
prev parent reply other threads:[~2021-06-18 3:46 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-17 8:23 [PATCH v2 0/3] netfs, afs: Fix netfs_write_begin and THP handling David Howells
2021-06-17 8:24 ` [PATCH v2 1/3] afs: Handle len being extending over page end in write_begin/write_end David Howells
2021-06-21 14:32 ` Matthew Wilcox
2021-06-17 8:24 ` [PATCH v2 2/3] afs: Fix afs_write_end() to handle short writes David Howells
2021-06-21 14:36 ` Matthew Wilcox
2021-06-17 8:24 ` [PATCH v2 3/3] netfs: fix test for whether we can skip read when writing beyond EOF David Howells
2021-06-21 14:50 ` Matthew Wilcox
2021-06-18 3:46 ` Al Viro [this message]
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