From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f47.google.com (mail-pa0-f47.google.com [209.85.220.47]) by kanga.kvack.org (Postfix) with ESMTP id 5B4806B0035 for ; Fri, 25 Jul 2014 12:32:40 -0400 (EDT) Received: by mail-pa0-f47.google.com with SMTP id kx10so6364215pab.20 for ; Fri, 25 Jul 2014 09:32:40 -0700 (PDT) Received: from mga09.intel.com (mga09.intel.com. [134.134.136.24]) by mx.google.com with ESMTP id du3si4859191pdb.245.2014.07.25.09.32.39 for ; Fri, 25 Jul 2014 09:32:39 -0700 (PDT) Message-ID: <53D286A5.7050100@intel.com> Date: Fri, 25 Jul 2014 09:32:37 -0700 From: Dave Hansen MIME-Version: 1.0 Subject: Re: Background page clearing References: <000001cfa81a$110d15c0$33274140$@com> <53D27590.2090500@intel.com> In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Wilco Dijkstra , "linux-mm@kvack.org" On 07/25/2014 09:27 AM, Wilco Dijkstra wrote: >> On 07/25/2014 08:06 AM, Wilco Dijkstra wrote: >>> Is there a reason Linux does not do background page clearing like other OSes to reduce this >>> overhead? It would be a good fit for typical mobile workloads (bursts of high activity >> followed by >>> periods of low activity). >> >> If the page is being allocated, it is about to be used and be brought in >> to the CPU's cache. If we zero it close to this use, we only pay to >> bring it in to the CPU's cache once. Or so goes the theory... > > I can see the reasoning for 4KB pages and small allocations (eg. stack), > but would that ever be true for huge pages? Probably not, but huge pages aren't allocated and freed enough in any workload that I know of for this to make a difference for them. >> I tried a zero-on-free implementation a year or so ago. It helped some >> workloads and hurt others. The gains were not large enough or >> widespread enough to merit pushing it in to the kernel. > > Was that literally zero-on-free or zero in the background? Was the result > the same for different page sizes? My guess is that the result will be > different for huge pages. Literally zero-on-free for 4k pages only. I did it inside the per-cpu-pages lists. -- 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