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Date: Tue, 31 Mar 2015 14:35:21 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
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)
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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?