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RE: [Xen-devel] Reducing impact of save/restore/dump on Dom0

  • To: "Iustin Pop" <iusty@xxxxxxxxx>
  • From: "Graham, Simon" <Simon.Graham@xxxxxxxxxxx>
  • Date: Tue, 6 Feb 2007 12:46:52 -0500
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Tue, 06 Feb 2007 09:46:29 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcdKFWT+Tx3rUcLvQHe1unTQiEZIxwAAGBvg
  • Thread-topic: [Xen-devel] Reducing impact of save/restore/dump on Dom0

> On linux, there is another way beside O_DIRECT: it's possible to
> the memory used for cached writing using the sysctl vm.dirty_ratio;
> I've
> used this to reduce the impact of heavy cached writes on dom0 with
> results.
> Maybe it helps for save/dump also...

Oh interesting -- I shall look into this. 

I just took a quick peek and it is set to 40% in Dom0; I do see free
memory go to zero during a dump (and save/restore) plus I see the
waitIO% go to near 100% and Dom0 becomes somewhat unresponsive;
specifically what we see is that domain boot fails during this time
because of a XenBus timeout waiting for the hotplug scripts to finish
adding the VBD in Dom0.

I still feel that dump/save/restore files really don't belong in the
system cache at all since they just pollute the cache for no ggood


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