From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx127.postini.com [74.125.245.127]) by kanga.kvack.org (Postfix) with SMTP id A8E2E6B002B for ; Wed, 12 Dec 2012 16:30:58 -0500 (EST) Date: Wed, 12 Dec 2012 13:30:51 -0800 From: Andrew Morton Subject: Re: [PATCH v5 09/11] thp: lazy huge zero page allocation Message-Id: <20121212133051.6dad3722.akpm@linux-foundation.org> In-Reply-To: <20121115094155.GG9676@otc-wbsnb-06> References: <1352300463-12627-1-git-send-email-kirill.shutemov@linux.intel.com> <1352300463-12627-10-git-send-email-kirill.shutemov@linux.intel.com> <20121115094155.GG9676@otc-wbsnb-06> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: David Rientjes , Andrea Arcangeli , linux-mm@kvack.org, Andi Kleen , "H. Peter Anvin" , linux-kernel@vger.kernel.org, "Kirill A. Shutemov" On Thu, 15 Nov 2012 11:41:55 +0200 "Kirill A. Shutemov" wrote: > On Wed, Nov 14, 2012 at 03:37:09PM -0800, David Rientjes wrote: > > On Wed, 7 Nov 2012, Kirill A. Shutemov wrote: > > > > > From: "Kirill A. Shutemov" > > > > > > Instead of allocating huge zero page on hugepage_init() we can postpone it > > > until first huge zero page map. It saves memory if THP is not in use. > > > > > > > Is it worth the branch on every non-write pagefault after that? The > > unlikely() is not going to help on x86. If thp is enabled in your > > .config (which isn't the default), then I think it's better to just > > allocate the zero huge page once and avoid any branches after that to > > lazily allocate it. (Or do it only when thp is set to "madvise" or > > "always" if booting with transparent_hugepage=never.) > > I can rewrite the check to static_key if you want. Would it be better? The new test-n-branch only happens on the first read fault against a thp huge page, yes? In which case it's a quite infrequent event and I suspect this isn't worth bothering about. -- 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