From: Jeremy Allison <jra@samba.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Jeremy Allison <jra@samba.org>,
Andrew Morton <akpm@linux-foundation.org>,
Milosz Tanski <milosz@adfin.com>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-aio@kvack.org, Mel Gorman <mgorman@suse.de>,
Volker Lendecke <Volker.Lendecke@sernet.de>,
Tejun Heo <tj@kernel.org>, Jeff Moyer <jmoyer@redhat.com>,
"Theodore Ts'o" <tytso@mit.edu>,
Al Viro <viro@zeniv.linux.org.uk>,
linux-api@vger.kernel.org,
Michael Kerrisk <mtk.manpages@gmail.com>,
linux-arch@vger.kernel.org, Dave Chinner <david@fromorbit.com>
Subject: Re: [PATCH v7 0/5] vfs: Non-blockling buffered fs read (page cache only)
Date: Mon, 30 Mar 2015 10:19:12 -0700 [thread overview]
Message-ID: <20150330171912.GB5835@samba2> (raw)
In-Reply-To: <20150330073604.GB22229@infradead.org>
On Mon, Mar 30, 2015 at 12:36:04AM -0700, Christoph Hellwig wrote:
> On Fri, Mar 27, 2015 at 08:58:54AM -0700, Jeremy Allison wrote:
> > The problem with the above is that we can't tell the difference
> > between pread2() returning a short read because the pages are not
> > in cache, or because someone truncated the file. So we need some
> > way to differentiate this.
>
> Is a race vs truncate really that time critical that you can't
> wait for the thread pool to do the second read to notice it?
Probably not, as this is the fallback path anyway.
> > My preference from userspace would be for pread2() to return
> > EAGAIN if *all* the data requested is not available (where
> > 'all' can be less than the size requested if the file has
> > been truncated in the meantime).
>
> That is easily implementable, but I can see that for example web apps
> would be happy to get as much as possible. So if Samba can be ok
> with short reads and only detecting the truncated case in the slow
> path that would make life simpler. Otherwise we might indeed need two
> flags.
Simpler is better. I can live with the partial read+fallback.
Jeremy.
WARNING: multiple messages have this Message-ID (diff)
From: Jeremy Allison <jra-eUNUBHrolfbYtjvyW6yDsg@public.gmane.org>
To: Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
Cc: Jeremy Allison <jra-eUNUBHrolfbYtjvyW6yDsg@public.gmane.org>,
Andrew Morton
<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
Milosz Tanski <milosz-B5zB6C1i6pkAvxtiuMwx3w@public.gmane.org>,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-aio-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org,
Mel Gorman <mgorman-l3A5Bk7waGM@public.gmane.org>,
Volker Lendecke
<Volker.Lendecke-3ekOc4rQMZmzQB+pC5nmwQ@public.gmane.org>,
Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
Jeff Moyer <jmoyer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
Theodore Ts'o <tytso-3s7WtUTddSA@public.gmane.org>,
Al Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>,
linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Michael Kerrisk
<mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
linux-arch-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Dave Chinner <david-FqsqvQoI3Ljby3iVrkZq2A@public.gmane.org>
Subject: Re: [PATCH v7 0/5] vfs: Non-blockling buffered fs read (page cache only)
Date: Mon, 30 Mar 2015 10:19:12 -0700 [thread overview]
Message-ID: <20150330171912.GB5835@samba2> (raw)
In-Reply-To: <20150330073604.GB22229-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
On Mon, Mar 30, 2015 at 12:36:04AM -0700, Christoph Hellwig wrote:
> On Fri, Mar 27, 2015 at 08:58:54AM -0700, Jeremy Allison wrote:
> > The problem with the above is that we can't tell the difference
> > between pread2() returning a short read because the pages are not
> > in cache, or because someone truncated the file. So we need some
> > way to differentiate this.
>
> Is a race vs truncate really that time critical that you can't
> wait for the thread pool to do the second read to notice it?
Probably not, as this is the fallback path anyway.
> > My preference from userspace would be for pread2() to return
> > EAGAIN if *all* the data requested is not available (where
> > 'all' can be less than the size requested if the file has
> > been truncated in the meantime).
>
> That is easily implementable, but I can see that for example web apps
> would be happy to get as much as possible. So if Samba can be ok
> with short reads and only detecting the truncated case in the slow
> path that would make life simpler. Otherwise we might indeed need two
> flags.
Simpler is better. I can live with the partial read+fallback.
Jeremy.
next prev parent reply other threads:[~2015-03-30 17:19 UTC|newest]
Thread overview: 94+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-16 18:27 [PATCH v7 0/5] vfs: Non-blockling buffered fs read (page cache only) Milosz Tanski
2015-03-16 18:27 ` [PATCH v7 1/5] vfs: Prepare for adding a new preadv/pwritev with user flags Milosz Tanski
2015-03-16 18:27 ` Milosz Tanski
2015-03-16 21:05 ` Andreas Dilger
2015-03-16 21:05 ` Andreas Dilger
2015-03-16 18:27 ` [PATCH v7 2/5] vfs: Define new syscalls preadv2,pwritev2 Milosz Tanski
2015-03-16 18:27 ` Milosz Tanski
2015-03-16 18:27 ` [PATCH v7 3/5] x86: wire up preadv2 and pwritev2 Milosz Tanski
2015-03-16 18:27 ` Milosz Tanski
2015-03-16 18:27 ` [PATCH v7 4/5] vfs: RWF_NONBLOCK flag for preadv2 Milosz Tanski
2015-03-16 18:27 ` Milosz Tanski
2015-03-16 18:27 ` [PATCH v7 5/5] xfs: add RWF_NONBLOCK support Milosz Tanski
2015-03-16 18:27 ` Milosz Tanski
2015-03-16 22:04 ` Dave Chinner
2015-03-16 18:32 ` [PATCH] Add preadv2/pwritev2 documentation Milosz Tanski
2015-03-27 16:49 ` Andrew Morton
2015-03-30 7:33 ` Christoph Hellwig
2015-03-30 7:33 ` Christoph Hellwig
2015-03-16 18:34 ` [PATCH] fstests: generic test for preadv2 behavior on linux Milosz Tanski
2015-03-16 18:34 ` Milosz Tanski
2015-03-16 21:07 ` Andreas Dilger
2015-03-16 21:07 ` Andreas Dilger
2015-03-16 22:03 ` Milosz Tanski
2015-03-16 22:02 ` Dave Chinner
2015-03-16 22:02 ` Dave Chinner
2015-03-16 22:11 ` Milosz Tanski
2015-03-16 22:56 ` Dave Chinner
2015-03-16 22:56 ` Dave Chinner
2015-03-26 11:55 ` [PATCH v7 0/5] vfs: Non-blockling buffered fs read (page cache only) Christoph Hellwig
2015-03-26 11:55 ` Christoph Hellwig
2015-03-26 19:12 ` Milosz Tanski
2015-03-26 19:12 ` Milosz Tanski
2015-03-27 2:26 ` Milosz Tanski
2015-03-27 2:29 ` Milosz Tanski
2015-03-27 2:29 ` Milosz Tanski
2015-03-27 3:28 ` Andrew Morton
2015-03-27 3:28 ` Andrew Morton
2015-03-27 5:41 ` Volker Lendecke
2015-03-27 5:41 ` Volker Lendecke
2015-03-27 6:08 ` Andrew Morton
2015-03-27 6:08 ` Andrew Morton
2015-03-27 8:02 ` Volker Lendecke
2015-03-27 8:02 ` Volker Lendecke
2015-03-27 8:12 ` Christoph Hellwig
2015-03-27 8:18 ` Christoph Hellwig
2015-03-27 8:18 ` Christoph Hellwig
2015-03-27 8:35 ` Andrew Morton
2015-03-27 8:35 ` Andrew Morton
2015-03-27 8:48 ` Christoph Hellwig
2015-03-27 9:01 ` Andrew Morton
2015-03-27 9:01 ` Andrew Morton
2015-03-27 9:44 ` Volker Lendecke
2015-03-27 15:58 ` Jeremy Allison
2015-03-27 15:58 ` Jeremy Allison
2015-03-27 16:30 ` Andrew Morton
2015-03-27 16:30 ` Andrew Morton
2015-03-27 16:30 ` Andrew Morton
2015-03-27 16:30 ` Andrew Morton
2015-03-27 16:39 ` Jeremy Allison
2015-03-27 16:39 ` Jeremy Allison
2015-03-27 16:39 ` Andrew Morton
2015-03-27 16:45 ` Milosz Tanski
2015-03-31 1:27 ` Milosz Tanski
2015-03-27 16:38 ` Milosz Tanski
2015-03-27 16:38 ` Milosz Tanski
2015-03-30 7:36 ` Christoph Hellwig
2015-03-30 17:19 ` Jeremy Allison [this message]
2015-03-30 17:19 ` Jeremy Allison
2015-03-30 22:51 ` Milosz Tanski
2015-03-30 20:26 ` Andrew Morton
2015-03-30 20:26 ` Andrew Morton
2015-03-30 20:32 ` Jeremy Allison
2015-03-30 20:37 ` Andrew Morton
2015-03-30 20:49 ` Jeremy Allison
2015-03-30 21:33 ` Andrew Morton
2015-03-30 22:35 ` Milosz Tanski
2015-03-30 22:49 ` Milosz Tanski
2015-03-30 22:57 ` Andrew Morton
2015-03-30 23:06 ` Milosz Tanski
2015-03-30 23:06 ` Milosz Tanski
2015-03-30 23:25 ` Milosz Tanski
2015-04-04 3:42 ` Andrew Morton
2015-04-06 3:53 ` Milosz Tanski
2015-04-06 3:53 ` Milosz Tanski
2015-03-30 23:09 ` Milosz Tanski
2015-03-27 15:21 ` Milosz Tanski
2015-03-27 15:21 ` Milosz Tanski
2015-03-27 17:04 ` Andrew Morton
2015-03-30 7:40 ` Christoph Hellwig
2015-03-30 7:40 ` Christoph Hellwig
2015-03-30 18:54 ` Andrew Morton
2015-03-30 22:40 ` Milosz Tanski
2015-03-30 22:50 ` Andrew Morton
2015-03-30 22:50 ` Andrew Morton
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20150330171912.GB5835@samba2 \
--to=jra@samba.org \
--cc=Volker.Lendecke@sernet.de \
--cc=akpm@linux-foundation.org \
--cc=david@fromorbit.com \
--cc=hch@infradead.org \
--cc=jmoyer@redhat.com \
--cc=linux-aio@kvack.org \
--cc=linux-api@vger.kernel.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mgorman@suse.de \
--cc=milosz@adfin.com \
--cc=mtk.manpages@gmail.com \
--cc=tj@kernel.org \
--cc=tytso@mit.edu \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.