From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx172.postini.com [74.125.245.172]) by kanga.kvack.org (Postfix) with SMTP id CC20B6B0044 for ; Sat, 1 Dec 2012 13:41:41 -0500 (EST) Received: by mail-ea0-f169.google.com with SMTP id a12so777626eaa.14 for ; Sat, 01 Dec 2012 10:41:40 -0800 (PST) Date: Sat, 1 Dec 2012 19:41:35 +0100 From: Ingo Molnar Subject: Re: [RFC PATCH] mm/migration: Remove anon vma locking from try_to_unmap() use Message-ID: <20121201184135.GA32449@gmail.com> References: <1354305521-11583-1-git-send-email-mingo@kernel.org> <20121201094927.GA12366@gmail.com> <20121201122649.GA20322@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Linus Torvalds 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 * Linus Torvalds wrote: > On Sat, Dec 1, 2012 at 4:26 AM, Ingo Molnar wrote: > > > > > > So as a quick concept hack I wrote the patch attached below. > > (It's not signed off, see the patch description text for the > > reason.) > > Well, it confirms that anon_vma locking is a big problem, but > as outlined in my other email it's completely incorrect from > an actual behavior standpoint. Yeah. > Btw, I think the anon_vma lock could be made a spinlock > instead of a mutex or rwsem, but that would probably take more > work. We *shouldn't* be doing anything that needs IO inside > the anon_vma lock, though, so it *should* be doable. But there > are probably quite a bit of allocations inside the lock, and I > know it covers huge areas, so a spinlock might not only be > hard to convert to, it quite likely has latency issues too. I'll try the rwsem and see how it goes? > Oh, btw, MUTEX_SPIN_ON_OWNER may well improve performance too, > but it gets disabled by DEBUG_MUTEXES. So some of the > performance impact of the vma locking may be *very* > kernel-config dependent. Hm, indeed. For performance runs I typically disable lock debugging - which might have made me not directly notice some of the performance problems. Thanks, Ingo -- 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