From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id 5FBA76B00A6 for ; Mon, 3 Jan 2011 02:41:03 -0500 (EST) Received: by vws10 with SMTP id 10so5449105vws.14 for ; Sun, 02 Jan 2011 23:41:00 -0800 (PST) MIME-Version: 1.0 In-Reply-To: References: Date: Mon, 3 Jan 2011 09:40:57 +0200 Message-ID: Subject: Re: Should we be using unlikely() around tests of GFP_ZERO? From: Pekka Enberg Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: Minchan Kim Cc: Theodore Ts'o , Christoph Lameter , Pekka Enberg , Matt Mackall , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Steven Rostedt , David Rientjes , npiggin@kernel.dk List-ID: Hi, On Mon, Jan 3, 2011 at 8:48 AM, Theodore Ts'o wrote: >> Given the patches being busily submitted by trivial patch submitters to >> make use kmem_cache_zalloc(), et. al, I believe we should remove the >> unlikely() tests around the (gfp_flags & __GFP_ZERO) tests, such as: >> >> - =A0 =A0 =A0 if (unlikely((flags & __GFP_ZERO) && objp)) >> + =A0 =A0 =A0 if ((flags & __GFP_ZERO) && objp) >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0memset(objp, 0, obj_size(cachep)); >> >> Agreed? =A0If so, I'll send a patch... On Mon, Jan 3, 2011 at 5:46 AM, Minchan Kim wrote: > I support it. I guess the rationale here is that if you're going to take the hit of memset() you can take the hit of unlikely() as well. We're optimizing for hot call-sites that allocate a small amount of memory and initialize everything themselves. That said, I don't think the unlikely() annotation matters much either way and am for removing it unless people object to that. On Mon, Jan 3, 2011 at 5:46 AM, Minchan Kim wrote: > Recently Steven tried to gather the information. > http://thread.gmane.org/gmane.linux.kernel/1072767 > Maybe he might have a number for that. That would be interesting, sure. -- 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/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org