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From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
To: Andrew Morton <akpm@linux-foundation.org>
CC: Mel Gorman <mgorman@suse.de>, Naoya Horiguchi <nao.horiguchi@gmail.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Hugh Dickins <hughd@google.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        David Rientjes <rientjes@google.com>, Rik van Riel <riel@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: numa: disable change protection for vma(VM_HUGETLB)
Thread-Topic: [PATCH] mm: numa: disable change protection for vma(VM_HUGETLB)
Thread-Index: AQHQa1RtvOznTUkTLkWQBP/X/X+ynJ02h6SAgABvgQA=
Date: Wed, 1 Apr 2015 04:14:27 +0000
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On Tue, Mar 31, 2015 at 02:35:21PM -0700, Andrew Morton wrote:
> On Tue, 31 Mar 2015 01:45:55 +0000 Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> wrote:
> 
> > Currently when a process accesses to hugetlb range protected with PROTNONE,
> > unexpected COWs are triggered, which finally put hugetlb subsystem into
> > broken/uncontrollable state, where for example h->resv_huge_pages is subtracted
> > too much and wrapped around to a very large number, and free hugepage pool
> > is no longer maintainable.
> > 
> > This patch simply stops changing protection for vma(VM_HUGETLB) to fix the
> > problem. And this also allows us to avoid useless overhead of minor faults.
> > 
> > ...
> >
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -2161,8 +2161,10 @@ void task_numa_work(struct callback_head *work)
> >  		vma = mm->mmap;
> >  	}
> >  	for (; vma; vma = vma->vm_next) {
> > -		if (!vma_migratable(vma) || !vma_policy_mof(vma))
> > +		if (!vma_migratable(vma) || !vma_policy_mof(vma) ||
> > +			is_vm_hugetlb_page(vma)) {
> >  			continue;
> > +		}
> >  
> >  		/*
> >  		 * Shared library pages mapped by multiple processes are not
> 
> Which kernel version(s) need this patch?

I don't bisect completely, but the problem this patch is mentioning is visible
since v4.0-rc1 (not reproduced at v3.19).

Thanks,
Naoya Horiguchi