linux-kernel - Re: [PATCH v2 10/10] thp: implement refcounting for huge zero page

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Date:	Mon, 10 Sep 2012 16:57:59 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	linux-kernel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill@...temov.name>
Subject: Re: [PATCH v2 10/10] thp: implement refcounting for huge zero page

On Mon, 2012-09-10 at 17:44 +0300, Kirill A. Shutemov wrote:


> Yes, disabling preemption before alloc_pages() and enabling after
> atomic_set() looks reasonable. Thanks.

In fact, as alloc_pages(GFP_TRANSHUGE | __GFP_ZERO, HPAGE_PMD_ORDER);
might sleep, it would be better to disable preemption after calling it :

zero_page = alloc_pages(GFP_TRANSHUGE | __GFP_ZERO, HPAGE_PMD_ORDER);
if (!zero_page)
	return 0;
preempt_disable();
if (cmpxchg(&huge_zero_pfn, 0, page_to_pfn(zero_page))) {
	preempt_enable();
	__free_page(zero_page);
	goto retry;
}
atomic_set(&huge_zero_refcount, 2);
preempt_enable();


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