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

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Message-ID: <20140219085917.GJ27965@twins.programming.kicks-ass.net>
Date:	Wed, 19 Feb 2014 09:59:17 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	riel@...hat.com
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	linux-mm@...ck.org, chegu_vinod@...com, aarcange@...hat.com,
	akpm@...ux-foundation.org
Subject: Re: [PATCH -mm 0/3] fix numa vs kvm scalability issue

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?
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