Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 28 Jan 2002 17:00:46 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 28 Jan 2002 17:00:36 -0500 Received: from vsdc01.corp.publichost.com ([64.7.196.123]:48909 "EHLO vsdc01.corp.publichost.com") by vger.kernel.org with ESMTP id ; Mon, 28 Jan 2002 17:00:29 -0500 Message-ID: <3C55C9F7.6010106@vitalstream.com> Date: Mon, 28 Jan 2002 14:00:23 -0800 From: Rick Stevens User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:0.9.5) Gecko/20011012 X-Accept-Language: en-us MIME-Version: 1.0 To: linux-kernel@vger.kernel.org Subject: Re: Note describing poor dcache utilization under high memory pressure In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Rik van Riel wrote: > On Mon, 28 Jan 2002, Rick Stevens wrote: > >>Daniel Phillips wrote: >>[snip] >> > [page table COW description] > > >>Perhaps I'm missing this, but I read that as the child gets a reference >>to the parent's memory. If the child attempts a write, then new memory >>is allocated, data copied and the write occurs to this new memory. As >>I read this, it's only invoked on a child write. >> >>Would this not leave a hole where the parent could write and, since the >>child shares that memory, the new data would be read by the child? Sort >>of a hidden shm segment? If so, I think we've got problems brewing. >>Now, if a parent write causes the same behaviour as a child write, then >>my point is moot. >> > > Daniel and I discussed this issue when Daniel first came up with > the idea of doing page table COW. He seemed a bit confused by > fork semantics when we first discussed this idea, too ;) > > You're right though, both parent and child need to react in the > same way, preferably _without_ having to walk all of the parent's > page tables and mark them read-only ... Ah, good! I wasn't losing it then. That's a relief! I've gotta read up on the kernel's VM system. I use to write them for a certain three-letter-acronymed company--many, many moons ago. Maybe I'd have some ideas. Then again, perhaps not. ---------------------------------------------------------------------- - Rick Stevens, SSE, VitalStream, Inc. rstevens@vitalstream.com - - 949-743-2010 (Voice) http://www.vitalstream.com - - - - Veni, Vidi, VISA: I came, I saw, I did a little shopping. - ---------------------------------------------------------------------- - 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/