Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752888Ab0AGQVf (ORCPT ); Thu, 7 Jan 2010 11:21:35 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752738Ab0AGQVe (ORCPT ); Thu, 7 Jan 2010 11:21:34 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:59728 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751230Ab0AGQVe (ORCPT ); Thu, 7 Jan 2010 11:21:34 -0500 Date: Thu, 7 Jan 2010 08:19:56 -0800 (PST) From: Linus Torvalds X-X-Sender: torvalds@localhost.localdomain To: Christoph Lameter cc: Arjan van de Ven , Peter Zijlstra , "Paul E. McKenney" , Peter Zijlstra , KAMEZAWA Hiroyuki , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "minchan.kim@gmail.com" , "hugh.dickins" , Nick Piggin , Ingo Molnar Subject: Re: [RFC][PATCH 6/8] mm: handle_speculative_fault() In-Reply-To: Message-ID: References: <20100104182429.833180340@chello.nl> <20100104182813.753545361@chello.nl> <20100105054536.44bf8002@infradead.org> <20100105192243.1d6b2213@infradead.org> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1692 Lines: 38 On Thu, 7 Jan 2010, Christoph Lameter wrote: > > > > depends on the workload; on a many-threads-java workload, you also get > > it for write quite a bit (lots of malloc/frees in userspace in addition > > to pagefaults).. at which point you do end up serializing on the > > zeroing. > > > > There's some real life real big workloads that show this pretty badly; > > so far the workaround is to have glibc batch up a lot of the free()s.. > > but that's just pushing it a little further out. > > Again mmap_sem is a rwsem and only a read lock is held. Zeroing in > do_anonymous_page can occur concurrently on multiple processors in the > same address space. The pte lock is intentionally taken *after* zeroing to > allow concurrent zeroing to occur. You're missing what Arjan said - the jav workload does a lot of memory allocations too, causing mmap/munmap. So now some paths are indeed holding it for writing (or need to wait for it to become writable). And the fairness of rwsems quite possibly then impacts throughput a _lot_.. (Side note: I wonder if we should wake up _all_ readers when we wake up any. Right now, we wake up all readers - but only until we hit a writer. Which is the _fair_ thing to do, but it does mean that we can end up in horrible patterns of alternating readers/writers, when it could be much better to just say "release the hounds" and let all pending readers go after a writer has had its turn). Linus -- 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/