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[Xen-devel] Re: [patch 28/34] Xen-pv_ops: Xen SMP guest support

To: Benjamin LaHaise <bcrl@xxxxxxxxx>
Subject: [Xen-devel] Re: [patch 28/34] Xen-pv_ops: Xen SMP guest support
From: Zachary Amsden <zach@xxxxxxxxxx>
Date: Wed, 14 Mar 2007 12:23:43 -0800
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Andi Kleen <ak@xxxxxx>, Rusty Russell <rusty@xxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, Andi Kleen <ak@xxxxxxx>, Chris Wright <chrisw@xxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxx, Ingo Molnar <mingo@xxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
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Benjamin LaHaise wrote:
+ * We aggressively remove defunct pgd from cr3. We execute unmap_vmas()
+ * *much* faster this way.
+ */

Are you switching mms in order to avoid all of the overhead associated with flushing an active mm during task exit? If so, it makes much more sense to do this in the generic helper, as it should be a win on x86 and x86-64 where switching to init_mm is relatively low cost given the support for global pages. I'll run some tests on a couple of systems this evening and post the results.

I tried this experiment on both x86 and x86-64 and I recall not seeing any effect. The mmu_gather optimization does most of this already.


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