From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx206.postini.com [74.125.245.206]) by kanga.kvack.org (Postfix) with SMTP id 93B3D6B0032 for ; Fri, 2 Aug 2013 17:36:11 -0400 (EDT) Received: by mail-wi0-f182.google.com with SMTP id hi8so998330wib.9 for ; Fri, 02 Aug 2013 14:36:10 -0700 (PDT) Date: Fri, 2 Aug 2013 23:36:07 +0200 From: Michal Hocko Subject: Re: [PATCH 1/4] mm, page_alloc: add likely macro to help compiler optimization Message-ID: <20130802213607.GA4742@dhcp22.suse.cz> References: <1375409279-16919-1-git-send-email-iamjoonsoo.kim@lge.com> <20130802162722.GA29220@dhcp22.suse.cz> <20130802204710.GX715@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130802204710.GX715@cmpxchg.org> Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: Joonsoo Kim , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Joonsoo Kim , Minchan Kim , Mel Gorman , Rik van Riel On Fri 02-08-13 16:47:10, Johannes Weiner wrote: > On Fri, Aug 02, 2013 at 06:27:22PM +0200, Michal Hocko wrote: > > On Fri 02-08-13 11:07:56, Joonsoo Kim wrote: > > > We rarely allocate a page with ALLOC_NO_WATERMARKS and it is used > > > in slow path. For making fast path more faster, add likely macro to > > > help compiler optimization. > > > > The code is different in mmotm tree (see mm: page_alloc: rearrange > > watermark checking in get_page_from_freelist) > > Yes, please rebase this on top. > > > Besides that, make sure you provide numbers which prove your claims > > about performance optimizations. > > Isn't that a bit overkill? We know it's a likely path (we would > deadlock constantly if a sizable portion of allocations were to ignore > the watermarks). Does he have to justify that likely in general makes > sense? That was more a generic comment. If there is a claim that something would be faster it would be nice to back that claim by some numbers (e.g. smaller hot path). In this particular case, unlikely(alloc_flags & ALLOC_NO_WATERMARKS) doesn't make any change to the generated code with gcc 4.8.1 resp. 4.3.4 I have here. Maybe other versions of gcc would benefit from the hint but changelog didn't tell us. I wouldn't add the anotation if it doesn't make any difference for the resulting code. -- Michal Hocko SUSE Labs -- 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