From: Dave Chinner <david@fromorbit.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Jeff Moyer <jmoyer@redhat.com>,
linux-nvdimm <linux-nvdimm@ml01.01.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Dave Chinner <dchinner@redhat.com>
Subject: Re: question: should io_is_direct really return true for DAX inodes?
Date: Fri, 30 Oct 2015 08:09:45 +1100 [thread overview]
Message-ID: <20151029210945.GA10656@dastard> (raw)
In-Reply-To: <CAPcyv4hoMCqtqFo-1C2DDZaf5w+SVSV3Cn+5BsLiE5ykv4soZg@mail.gmail.com>
On Fri, Oct 30, 2015 at 04:37:36AM +0900, Dan Williams wrote:
> [ reply-all re-send, sorry for the duplicate Jeff. ]
>
> On Thu, Oct 29, 2015 at 11:32 PM, Jeff Moyer <jmoyer@redhat.com> wrote:
> > Hi,
> >
> > I'm concerned that applications that used to run out of page cache will
> > experience a performance degradation when being forced into doing I/O
> > directly to the backing store. What do others think?
>
> I would think this is only a problem in the case where the media is
> orders of magnitude slower than page cache. That isn't the case with
> pmem.
If you're really concerned, I'm addressing this on XFS by making DAX
per-inode selectable (i.e the mount option needs to die). In which
case, users can have the best of both worlds - files marked as DAX
use DAX/direct IO, files that aren't marked can cache and suffer the
lower performance that all that page allocation, dirty tracking and
writeback via memcpy entails..
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
prev parent reply other threads:[~2015-10-29 21:10 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-29 14:32 question: should io_is_direct really return true for DAX inodes? Jeff Moyer
2015-10-29 19:37 ` Dan Williams
2015-10-29 21:09 ` Dave Chinner [this message]
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