From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx184.postini.com [74.125.245.184]) by kanga.kvack.org (Postfix) with SMTP id 6D3F96B0071 for ; Tue, 10 Jul 2012 11:24:42 -0400 (EDT) Received: by obhx4 with SMTP id x4so114188obh.14 for ; Tue, 10 Jul 2012 08:24:41 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20120710104722.GB14154@suse.de> References: <1341588521-17744-1-git-send-email-js1304@gmail.com> <20120710104722.GB14154@suse.de> Date: Wed, 11 Jul 2012 00:24:41 +0900 Message-ID: Subject: Re: [PATCH] mm: don't invoke __alloc_pages_direct_compact when order 0 From: JoonSoo Kim Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: David Rientjes , akpm@linux-foundation.org, Pekka Enberg , Christoph Lameter , linux-kernel@vger.kernel.org, linux-mm@kvack.org 2012/7/10 Mel Gorman : > You say that invoking the function is very costly. I agree that a function > call with that many parameters is hefty but it is also in the slow path of > the allocator. For order-0 allocations we are about to enter direct reclaim > where I would expect the cost far exceeds the cost of a function call. Yes, I agree. > If the cost is indeed high and you have seen this in profiles then I > suggest you create a forced inline function alloc_pages_direct_compact > that does this; > > if (order != 0) > __alloc_pages_direct_compact(...) > > and then call alloc_pages_direct_compact instead of > __alloc_pages_direct_compact. After that, recheck the profiles (although I > expect the difference to be marginal) and the size of vmlinux (if it gets > bigger, it's probably not worth it). > That would be functionally similar to your patch but it will preserve git > blame, churn less code and be harder to make mistakes with in the unlikely > event a third call to alloc_pages_direct_compact is ever added. Your suggestion looks good. But, the size of page_alloc.o is more than before. I test 3 approaches, vanilla, always_inline and wrapping(alloc_page_direct_compact which is your suggestion). In my environment (v3.5-rc5, gcc 4.6.3, x86_64), page_alloc.o shows below number. total, .text section, .text.unlikely page_alloc_vanilla.o: 93432, 0x510a, 0x243 page_alloc_inline.o: 93336, 0x52ca, 0xa4 page_alloc_wrapping.o: 93528, 0x515a, 0x238 Andrew said that inlining add only 26 bytes to .text of page_alloc.o, but in my system, need more bytes. Currently, I think this patch doesn't have obvious benefit, so I want to drop it. Any objections? Thanks for good comments. -- 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