linux-kernel - Re: [PATCH -mm 0/3] fix numa vs kvm scalability issue

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Message-Id: <20140219112803.75c6daf470dad88eb10f5dab@linux-foundation.org>
Date:	Wed, 19 Feb 2014 11:28:03 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	riel@...hat.com, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	linux-mm@...ck.org, chegu_vinod@...com, aarcange@...hat.com
Subject: Re: [PATCH -mm 0/3] fix numa vs kvm scalability issue

On Wed, 19 Feb 2014 09:59:17 +0100 Peter Zijlstra <peterz@...radead.org> wrote:

> On Tue, Feb 18, 2014 at 05:12:43PM -0500, riel@...hat.com wrote:
> > The NUMA scanning code can end up iterating over many gigabytes
> > of unpopulated memory, especially in the case of a freshly started
> > KVM guest with lots of memory.
> > 
> > This results in the mmu notifier code being called even when
> > there are no mapped pages in a virtual address range. The amount
> > of time wasted can be enough to trigger soft lockup warnings
> > with very large (>2TB) KVM guests.
> > 
> > This patch moves the mmu notifier call to the pmd level, which
> > represents 1GB areas of memory on x86-64. Furthermore, the mmu
> > notifier code is only called from the address in the PMD where
> > present mappings are first encountered.
> > 
> > The hugetlbfs code is left alone for now; hugetlb mappings are
> > not relocatable, and as such are left alone by the NUMA code,
> > and should never trigger this problem to begin with.
> > 
> > The series also adds a cond_resched to task_numa_work, to
> > fix another potential latency issue.
> 
> Andrew, I'll pick up the first kernel/sched/ patch; do you want the
> other two mm/ patches?

That works, thanks.
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