[dm-devel] [PATCH 8/9] dm crypt: offload writes to thread

[Mike Snitzer]

On Tue, Apr 01 2014 at  2:15pm -0400,
Mikulas Patocka <mpatocka at redhat.com> wrote:

> 
> 
> On Tue, 1 Apr 2014, Mike Snitzer wrote:
> 
> > On Tue, Apr 01 2014 at 12:27pm -0400,
> > Ondrej Kozina <okozina at redhat.com> wrote:
> > 
> > > On 03/28/2014 09:11 PM, Mike Snitzer wrote:
> > > >From: Mikulas Patocka <mpatocka at redhat.com>
> > > >
> > > >Submitting write bios directly in the encryption thread caused serious
> > > >performance degradation.  On a multiprocessor machine, encryption requests
> > > >finish in a different order than they were submitted.  Consequently, write
> > > >requests would be submitted in a different order and it could cause severe
> > > >performance degradation.
> > > > (...)
> > > 
> > > Hi,
> > > 
> > > originally I planed to post result of performance testing but
> > > unfortunately I crashed the test machine several times with
> > > <in_subject> patch applied and onward:
> > > 
> > > The test set up looks following:
> > > 
> > > the base is kernel-3.14-rc8 with applied "[PATCH 2/9] block: use
> > > kmalloc alignment for bio slab"
> > > 
> > > On top of base I compiled various dm-crypt modules:
> > > 
> > > <no_patch>		= raw 3.14-rc8 dm-crypt module
> > > <no_percpu>		= "[PATCH 1/9]"
> > > <per_bio_data>		= <no_percpu> + "[PATCH 3/9]"
> > > <unbound>		= <per_bio_data> + "[PATCH 4/9]"
> > > <dont_allocate_wfix>	= <unbound> + "[PATCH 5/9]" + "[PATCH 6/9]"
> > > <remove_io_pool>	= <dont_allocate_wfix> + "[PATCH 7/9]"
> > > <offload>		= <remove_io_pool> + "[PATCH 8/9]"
> > > <sort>			= <offload> + "[PATCH 9/9]"
> > 
> > Wonder if it worthwhile to rebase to final v3.14... could this
> > bio_add_page/mm crash be a function of something since fixed late in the
> > rc cycle?
> 
> ... or try it without XFS. XFS corrupts memory on I/O error 
> (https://bugzilla.redhat.com/show_bug.cgi?id=924301), so it may be that.
> 
> Can the bug be reproduced if you modify the test to use ext2, ext3 or ext4 
> instead of xfs?

Or apply the patch that fixes the XFS use after free:
http://marc.info/?l=linux-xfs&m=139545654311177&q=raw