7:32 a.m.
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?
Cheers,
Jeff
12:37 p.m.
[ reply-all re-send, sorry for the duplicate Jeff. ]
On Thu, Oct 29, 2015 at 11:32 PM, Jeff Moyer <jmoyer(a)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.
2:09 p.m.
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(a)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(a)fromorbit.com
1910
days inactive
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2 comments
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Dan Williams -
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Jeff Moyer