From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx196.postini.com [74.125.245.196]) by kanga.kvack.org (Postfix) with SMTP id 3073E6B005D for ; Mon, 10 Sep 2012 10:02:45 -0400 (EDT) Received: by eeke49 with SMTP id e49so1347880eek.14 for ; Mon, 10 Sep 2012 07:02:43 -0700 (PDT) Subject: Re: [PATCH v2 10/10] thp: implement refcounting for huge zero page From: Eric Dumazet In-Reply-To: <1347282813-21935-11-git-send-email-kirill.shutemov@linux.intel.com> References: <1347282813-21935-1-git-send-email-kirill.shutemov@linux.intel.com> <1347282813-21935-11-git-send-email-kirill.shutemov@linux.intel.com> Content-Type: text/plain; charset="UTF-8" Date: Mon, 10 Sep 2012 16:02:39 +0200 Message-ID: <1347285759.1234.1645.camel@edumazet-glaptop> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: Andrew Morton , Andrea Arcangeli , linux-mm@kvack.org, Andi Kleen , "H. Peter Anvin" , linux-kernel@vger.kernel.org, "Kirill A. Shutemov" On Mon, 2012-09-10 at 16:13 +0300, Kirill A. Shutemov wrote: > From: "Kirill A. Shutemov" > > H. Peter Anvin doesn't like huge zero page which sticks in memory forever > after the first allocation. Here's implementation of lockless refcounting > for huge zero page. > ... > +static unsigned long get_huge_zero_page(void) > +{ > + struct page *zero_page; > +retry: > + if (likely(atomic_inc_not_zero(&huge_zero_refcount))) > + return ACCESS_ONCE(huge_zero_pfn); > + > + zero_page = alloc_pages(GFP_TRANSHUGE | __GFP_ZERO, HPAGE_PMD_ORDER); > + if (!zero_page) > + return 0; > + if (cmpxchg(&huge_zero_pfn, 0, page_to_pfn(zero_page))) { > + __free_page(zero_page); > + goto retry; > + } This might break if preemption can happen here ? The second thread might loop forever because huge_zero_refcount is 0, and huge_zero_pfn not zero. If preemption already disabled, a comment would be nice. > + > + /* We take additional reference here. It will be put back by shinker */ typo : shrinker > + atomic_set(&huge_zero_refcount, 2); > + return ACCESS_ONCE(huge_zero_pfn); > +} > + -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org