From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id E892660021B for ; Sat, 2 Jan 2010 16:45:55 -0500 (EST) Subject: Re: [RFC PATCH] asynchronous page fault. From: Benjamin Herrenschmidt In-Reply-To: <20091225105140.263180e8.kamezawa.hiroyu@jp.fujitsu.com> References: <20091225105140.263180e8.kamezawa.hiroyu@jp.fujitsu.com> Content-Type: text/plain; charset="UTF-8" Date: Sun, 03 Jan 2010 08:45:33 +1100 Message-ID: <1262468733.2173.251.camel@pasglop> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "minchan.kim@gmail.com" , cl@linux-foundation.org List-ID: On Fri, 2009-12-25 at 10:51 +0900, KAMEZAWA Hiroyuki wrote: > Speculative page fault v3. > > This version is much simpler than old versions and doesn't use mm_accessor > but use RCU. This is based on linux-2.6.33-rc2. > > This patch is just my toy but shows... > - Once RB-tree is RCU-aware and no-lock in readside, we can avoid mmap_sem > in page fault. > So, what we need is not mm_accessor, but RCU-aware RB-tree, I think. > > But yes, I may miss something critical ;) > > After patch, statistics perf show is following. Test progam is attached. One concern I have with this, not that it can't be addressed but we'll have to be extra careful, is that the mmap_sem in the page fault path tend to protect more than just the VMA tree. One example on powerpc is the slice map used to keep track of page sizes. I would also need some time to convince myself that I don't have some bits of the MMU hash code that doesn't assume that holding the mmap_sem for writing prevents a PTE from being changed from !present to present. I wouldn't be surprised if there were more around fancy users of ->fault(), things like spufs, the DRM, etc... Cheers, Ben. -- 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