Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758431Ab3HMXKY (ORCPT ); Tue, 13 Aug 2013 19:10:24 -0400 Received: from relay2.sgi.com ([192.48.179.30]:47479 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1756090Ab3HMXKW (ORCPT ); Tue, 13 Aug 2013 19:10:22 -0400 Date: Tue, 13 Aug 2013 18:10:20 -0500 From: Nathan Zimmer To: Linus Torvalds Cc: Mike Travis , Nathan Zimmer , Peter Anvin , Ingo Molnar , Linux Kernel Mailing List , linux-mm , Robin Holt , Rob Landley , Daniel J Blueman , Andrew Morton , Greg Kroah-Hartman , Yinghai Lu , Mel Gorman Subject: Re: [RFC v3 0/5] Transparent on-demand struct page initialization embedded in the buddy allocator Message-ID: <20130813231020.GA22667@asylum.americas.sgi.com> References: <1375465467-40488-1-git-send-email-nzimmer@sgi.com> <1376344480-156708-1-git-send-email-nzimmer@sgi.com> <520A6DFC.1070201@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1995 Lines: 41 On Tue, Aug 13, 2013 at 10:51:37AM -0700, Linus Torvalds wrote: > I realize that benchmarking cares, and yes, I also realize that some > benchmarks actually want to reboot the machine between some runs just > to get repeatability, but if you're benchmarking a 16TB machine I'm > guessing any serious benchmark that actually uses that much memory is > going to take many hours to a few days to run anyway? Having some way > to wait until the memory is all done (which might even be just a silly > shell script that does "ps" and waits for the kernel threads to all go > away) isn't going to kill the benchmark - and the benchmark itself > will then not have to worry about hittinf the "oops, I need to > initialize 2GB of RAM now because I hit an uninitialized page". > I am not overly concerned with cost having to setup a page struct on first touch but what I need to avoid is adding more permanent cost to page faults on a system that is already "primed". > Ok, so I don't know all the issues, and in many ways I don't even > really care. You could do it other ways, I don't think this is a big > deal. The part I hate is the runtime hook into the core MM page > allocation code, so I'm just throwing out any random thing that comes > to my mind that could be used to avoid that part. > The only mm structure we are adding to is a new flag in page->flags. That didn't seem too much. I had hoped to restrict the core mm changes to check_new_page and free_pages_check but I haven't gotten there yet. Not putting on uninitialized pages on to the lru would work but then I would be concerned over any calculations based on totalpages. I might be too paranoid there but having that be incorrect until after a system is booted worries me. Nate -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/