From: Christoph Hellwig <hch@infradead.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@infradead.org>,
Davidlohr Bueso <dave@stgolabs.net>,
Waiman Long <Waiman.Long@hpe.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, x86@kernel.org,
linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org,
linux-s390@vger.kernel.org, linux-arch@vger.kernel.org,
linux-doc@vger.kernel.org, Jason Low <jason.low2@hp.com>,
Jonathan Corbet <corbet@lwn.net>,
Scott J Norton <scott.norton@hpe.com>,
Douglas Hatch <doug.hatch@hpe.com>
Subject: Re: [RFC PATCH-tip v4 02/10] locking/rwsem: Stop active read lock ASAP
Date: Mon, 10 Oct 2016 02:34:34 -0700 [thread overview]
Message-ID: <20161010093434.GA18024@infradead.org> (raw)
In-Reply-To: <20161010060745.GA27872@dastard>
On Mon, Oct 10, 2016 at 05:07:45PM +1100, Dave Chinner wrote:
> > > *However*, the DAX IO path locking in XFS has changed in 4.9-rc1 to
> > > match the buffered IO single writer POSIX semantics - the test is a
> > > bad test based on the fact it exercised a path that is under heavy
> > > development and so can't be used as a regression test across
> > > multiple kernels.
> >
> > That being said - I wonder if we should allow the shared lock on DAX
> > files IFF the user is specifying O_DIRECT in the open mode..
>
> It should do - if it doesn't then we screwed up the IO path
> selection logic in XFS and we'll need to fix it.
Depends on your defintion of "we". The DAX code has always abused the
direct I/O path, and that abuse is ingrained in the VFS path in a way that
we can't easily undo it in XFS, e.g. take a look at io_is_direct and
iocb_flags in include/linux/fs.h, which ensure that DAX I/O will always
appear as IOCB_DIRECT to the fs. It will take some time to untagle
this, but it's on my todo list once the last file system (ext4)
untangles the DAX and direct I/O path.
WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@infradead.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@infradead.org>,
Davidlohr Bueso <dave@stgolabs.net>,
Waiman Long <Waiman.Long@hpe.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, x86@kernel.org,
linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org,
linux-s390@vger.kernel.org, linux-arch@vger.kernel.org,
linux-doc@vger.kernel.org, Jason Low <jason.low2@hp.com>,
Jonathan Corbet <corbet@lwn.net>,
Scott J Norton <scott.norton@hpe.com>,
Douglas Hatch <doug.hatch@hpe.com>
Subject: Re: [RFC PATCH-tip v4 02/10] locking/rwsem: Stop active read lock ASAP
Date: Mon, 10 Oct 2016 09:34:34 +0000 [thread overview]
Message-ID: <20161010093434.GA18024@infradead.org> (raw)
In-Reply-To: <20161010060745.GA27872@dastard>
On Mon, Oct 10, 2016 at 05:07:45PM +1100, Dave Chinner wrote:
> > > *However*, the DAX IO path locking in XFS has changed in 4.9-rc1 to
> > > match the buffered IO single writer POSIX semantics - the test is a
> > > bad test based on the fact it exercised a path that is under heavy
> > > development and so can't be used as a regression test across
> > > multiple kernels.
> >
> > That being said - I wonder if we should allow the shared lock on DAX
> > files IFF the user is specifying O_DIRECT in the open mode..
>
> It should do - if it doesn't then we screwed up the IO path
> selection logic in XFS and we'll need to fix it.
Depends on your defintion of "we". The DAX code has always abused the
direct I/O path, and that abuse is ingrained in the VFS path in a way that
we can't easily undo it in XFS, e.g. take a look at io_is_direct and
iocb_flags in include/linux/fs.h, which ensure that DAX I/O will always
appear as IOCB_DIRECT to the fs. It will take some time to untagle
this, but it's on my todo list once the last file system (ext4)
untangles the DAX and direct I/O path.
next prev parent reply other threads:[~2016-10-10 9:34 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-18 21:11 [RFC PATCH-tip v4 00/10] locking/rwsem: Enable reader optimistic spinning Waiman Long
2016-08-18 21:11 ` Waiman Long
2016-08-18 21:11 ` [RFC PATCH-tip v4 01/10] locking/osq: Make lock/unlock proper acquire/release barrier Waiman Long
2016-08-18 21:11 ` Waiman Long
2016-10-04 19:06 ` Davidlohr Bueso
2016-10-04 19:06 ` Davidlohr Bueso
2016-10-04 21:28 ` Jason Low
2016-10-04 21:28 ` Jason Low
2016-10-05 12:19 ` Waiman Long
2016-10-05 12:19 ` Waiman Long
2016-10-05 12:19 ` Waiman Long
2016-10-05 15:11 ` Waiman Long
2016-10-05 15:11 ` Waiman Long
2016-10-05 15:11 ` Waiman Long
2016-10-06 5:47 ` Davidlohr Bueso
2016-10-06 5:47 ` Davidlohr Bueso
2016-10-06 19:30 ` Waiman Long
2016-10-06 19:30 ` Waiman Long
2016-10-06 19:30 ` Waiman Long
2016-10-10 5:39 ` [PATCH] locking/osq: Provide proper lock/unlock and relaxed flavors Davidlohr Bueso
2016-10-10 5:39 ` Davidlohr Bueso
2016-10-06 19:31 ` [RFC PATCH-tip v4 01/10] locking/osq: Make lock/unlock proper acquire/release barrier Jason Low
2016-10-06 19:31 ` Jason Low
2016-10-06 19:31 ` Jason Low
2016-08-18 21:11 ` [RFC PATCH-tip v4 02/10] locking/rwsem: Stop active read lock ASAP Waiman Long
2016-08-18 21:11 ` Waiman Long
2016-10-06 18:17 ` Davidlohr Bueso
2016-10-06 18:17 ` Davidlohr Bueso
2016-10-06 21:47 ` Dave Chinner
2016-10-06 21:47 ` Dave Chinner
2016-10-06 22:51 ` Davidlohr Bueso
2016-10-06 22:51 ` Davidlohr Bueso
2016-10-07 21:45 ` Waiman Long
2016-10-07 21:45 ` Waiman Long
2016-10-07 21:45 ` Waiman Long
2016-10-09 15:17 ` Christoph Hellwig
2016-10-09 15:17 ` Christoph Hellwig
2016-10-10 6:07 ` Dave Chinner
2016-10-10 6:07 ` Dave Chinner
2016-10-10 9:34 ` Christoph Hellwig [this message]
2016-10-10 9:34 ` Christoph Hellwig
2016-10-11 21:06 ` Dave Chinner
2016-10-11 21:06 ` Dave Chinner
2016-10-16 5:57 ` Christoph Hellwig
2016-10-16 5:57 ` Christoph Hellwig
2016-08-18 21:11 ` [RFC PATCH-tip v4 03/10] locking/rwsem: Make rwsem_spin_on_owner() return a tri-state value Waiman Long
2016-08-18 21:11 ` Waiman Long
2016-08-18 21:11 ` [RFC PATCH-tip v4 04/10] locking/rwsem: Enable count-based spinning on reader Waiman Long
2016-08-18 21:11 ` Waiman Long
2016-08-18 21:11 ` [RFC PATCH-tip v4 05/10] locking/rwsem: move down rwsem_down_read_failed function Waiman Long
2016-08-18 21:11 ` Waiman Long
2016-08-18 21:11 ` [RFC PATCH-tip v4 06/10] locking/rwsem: Move common rwsem macros to asm-generic/rwsem_types.h Waiman Long
2016-08-18 21:11 ` Waiman Long
2016-08-18 21:11 ` [RFC PATCH-tip v4 07/10] locking/rwsem: Change RWSEM_WAITING_BIAS for better disambiguation Waiman Long
2016-08-18 21:11 ` Waiman Long
2016-08-19 5:57 ` Wanpeng Li
2016-08-19 5:57 ` Wanpeng Li
2016-08-19 16:21 ` Waiman Long
2016-08-19 16:21 ` Waiman Long
2016-08-19 16:21 ` Waiman Long
2016-08-22 2:15 ` Wanpeng Li
2016-08-22 2:15 ` Wanpeng Li
2016-08-18 21:11 ` [RFC PATCH-tip v4 08/10] locking/rwsem: Enable spinning readers Waiman Long
2016-08-18 21:11 ` Waiman Long
2016-08-18 21:11 ` [RFC PATCH-tip v4 09/10] locking/rwsem: Enable reactivation of reader spinning Waiman Long
2016-08-18 21:11 ` Waiman Long
2016-08-18 21:11 ` [RFC PATCH-tip v4 10/10] locking/rwsem: Add a boot parameter to reader spinning threshold Waiman Long
2016-08-18 21:11 ` Waiman Long
2016-08-24 1:46 ` [lkp] [locking/rwsem] INFO: rcu_preempt detected stalls on CPUs/tasks kernel test robot
2016-08-24 1:46 ` kernel test robot
2016-08-24 1:46 ` [lkp] " kernel test robot
2016-08-24 4:00 ` [RFC PATCH-tip v4 10/10] locking/rwsem: Add a boot parameter to reader spinning threshold Davidlohr Bueso
2016-08-24 4:00 ` Davidlohr Bueso
2016-08-24 18:39 ` Waiman Long
2016-08-24 18:39 ` Waiman Long
2016-08-24 18:39 ` Waiman Long
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