[sheepdog] [PATCH] sheep: implement a correct detection of object cache pushing completion

[Hitoshi Mitake]

At Sat, 27 Jul 2013 15:08:34 +0200,
Ing. Luca Lazzeroni - Trend Servizi Srl wrote:
> 
> Il 26/07/2013 16:01, Hitoshi Mitake ha scritto:
> > At Fri, 26 Jul 2013 15:41:28 +0200,
> > Ing. Luca Lazzeroni - Trend Servizi Srl wrote:
> >> Il 24/07/2013 12:46, Hitoshi Mitake ha scritto:
> >>> Current implementation for pushing object cache would have a bug. In
> >>> object_cache_push(), the variable oc->push_count is incremented in the
> >>> loop of queuing work. This can produce a non deterministic bug when
> >>> a sequence of scheduling like below happens:
> >> Hi Hitoshi,
> >> I've tried to apply the patch as you suggested, but it isn't applyable 
> >> to sheepdog-stable since:
> >>
> >> object_cache.c:888:1: error: ‘struct object_cache’ has no member named 
> >> ‘dirty_count’
> >>
> >> Maybe code needs some refactor for succesfuly back-port it to 0.6-stable..
> > Hi Luca,
> >
> > I updated stable-0.6 for fixing the problem of object cache. Could you
> > test the latest stable-0.6?
> >
> > Thanks,
> > Hitoshi
> Hi,
> I've tested your patch in our production network.
> Using my script, I've made 4 different backups of a VM generating high
> I/O (rsync of about 100 GB of data) by using the pattern:
> 
> 1) Suspend vm
> 2) Take snapshot via "collie vdi snapshot"
> 3) Resume vm
> 4) Copy snapshot to external storage via "qemu-img convert"
> 
> Everything worked without segfaults and, it seems, with better
> performances than before.
> 
> Thank for your work,

Hi Luca,

Thanks a lot for your testing and reporting! It would also be helpful
for other users.

Thanks,
Hitoshi