From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx139.postini.com [74.125.245.139]) by kanga.kvack.org (Postfix) with SMTP id 0212D6B0073 for ; Fri, 30 Nov 2012 15:38:10 -0500 (EST) Received: by mail-wi0-f181.google.com with SMTP id hm9so385613wib.8 for ; Fri, 30 Nov 2012 12:38:09 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <1354305521-11583-1-git-send-email-mingo@kernel.org> References: <1354305521-11583-1-git-send-email-mingo@kernel.org> From: Linus Torvalds Date: Fri, 30 Nov 2012 12:37:49 -0800 Message-ID: Subject: Re: [PATCH 00/10] Latest numa/core release, v18 Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Ingo Molnar Cc: Linux Kernel Mailing List , linux-mm , Peter Zijlstra , Paul Turner , Lee Schermerhorn , Christoph Lameter , Rik van Riel , Mel Gorman , Andrew Morton , Andrea Arcangeli , Thomas Gleixner , Johannes Weiner , Hugh Dickins On Fri, Nov 30, 2012 at 11:58 AM, Ingo Molnar wrote: > > When pushed hard enough via threaded workloads (for example via the > numa02 test) then the upstream page migration code in mm/migration.c > becomes unscalable, resulting in lot of scheduling on the anon vma > mutex and a subsequent drop in performance. Ugh. I wonder if migration really needs that thing to be a mutex? I may be wrong, but the anon_vma lock only protects the actual rmap chains, and migration only ever changes the pte *contents*, not the actual chains of pte's themselves, right? So if this is a migration-specific scalability issue, then it might be possible to solve by making the mutex be a rwsem instead, and have migration only take it for reading. Of course, I'm quite possibly wrong, and the code depends on full mutual exclusion. Just a thought, in case it makes somebody go "Hmm.." Linus -- 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