Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755554Ab2FWQIX (ORCPT ); Sat, 23 Jun 2012 12:08:23 -0400 Received: from Mycroft.westnet.com ([216.187.52.7]:59713 "EHLO mycroft.westnet.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754117Ab2FWQIW (ORCPT ); Sat, 23 Jun 2012 12:08:22 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <20453.59620.255516.321417@quad.stoffel.home> Date: Sat, 23 Jun 2012 12:03:48 -0400 From: "John Stoffel" To: Andrew Morton Cc: "John Stoffel" , Rik van Riel , linux-mm@kvack.org, aarcange@redhat.com, peterz@infradead.org, minchan@gmail.com, kosaki.motohiro@gmail.com, andi@firstfloor.org, hannes@cmpxchg.org, mel@csn.ul.ie, linux-kernel@vger.kernel.org Subject: Re: [PATCH -mm v2 00/11] mm: scalable and unified arch_get_unmapped_area In-Reply-To: <20120622144714.440f8529.akpm@linux-foundation.org> References: <1340315835-28571-1-git-send-email-riel@surriel.com> <20452.32826.165122.958868@quad.stoffel.home> <20120622144714.440f8529.akpm@linux-foundation.org> X-Mailer: VM 8.1.2 under 23.2.1 (x86_64-pc-linux-gnu) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1808 Lines: 49 >>>>> "Andrew" == Andrew Morton writes: Andrew> On Fri, 22 Jun 2012 10:24:58 -0400 Andrew> "John Stoffel" wrote: >> >>>>> "Rik" == Rik van Riel writes: >> Rik> A long time ago, we decided to limit the number of VMAs per Rik> process to 64k. As it turns out, there actually are programs Rik> using tens of thousands of VMAs. >> >> Rik> Performance >> Rik> Testing performance with a benchmark that allocates tens Rik> of thousands of VMAs, unmaps them and mmaps them some more Rik> in a loop, shows promising results. >> >> How are the numbers for applications which only map a few VMAs? Is >> there any impact there? >> Andrew> Johannes did a test for that: https://lkml.org/lkml/2012/6/22/219 I don't see that in his results. But maybe (probably) I don't understand what types of applications this change is supposed to help. I guess I worry that this will just keep slowing down other apps. His tests seemed to be for just one VMA remapped with thousands in use. Or am I missing the fact that all VMAs are in the same pool? Andrew> Some regression with such a workload is unavoidable, I expect. Andrew> We have to work out whether the pros outweigh the cons. This Andrew> involves handwaving. Yup, it does. Proof by vigorous handwaving is a time honored tradition. And I do see that the numbers aren't that much poorer, I just keep thinking that if we can speed up the corner case, can't we also speed up the normal case with a better algorithm or data structure? John -- 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/