Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 28 Jan 2002 18:23:03 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 28 Jan 2002 18:22:45 -0500 Received: from dsl-213-023-039-090.arcor-ip.net ([213.23.39.90]:24199 "EHLO starship.berlin") by vger.kernel.org with ESMTP id ; Mon, 28 Jan 2002 18:22:34 -0500 Content-Type: text/plain; charset=US-ASCII From: Daniel Phillips To: Rick Stevens , linux-kernel@vger.kernel.org Subject: Re: Note describing poor dcache utilization under high memory pressure Date: Tue, 29 Jan 2002 00:27:29 +0100 X-Mailer: KMail [version 1.3.2] In-Reply-To:

<3C55DAEF.7020500@vitalstream.com> In-Reply-To: <3C55DAEF.7020500@vitalstream.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7BIT Message-Id: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On January 29, 2002 12:12 am, Rick Stevens wrote: > Daniel Phillips wrote: > > > Since the page was copied to the child, the child's page table must be > > altered, and since it is shared, it must first be instantiated by the child. > > So after all the dust settles, the parent and child have their own copies of > > a page table page, which differ only at a single location: the child's page > > table points at its freshly made CoW copy, and the parent's page table points > > at the original page. > > > > > The beauty of this is, the page table could just as easily have been shared > > by a sibling of the child, not the parent at all, in the case that the parent > > had already instantiated its own copy of the page table page because of an > > earlier CoW. > > > Ok. Still seems like a bit more copying than necessary. I think I can show that it's exactly as much copying as necessary, and no more. Oh, the page directory could also be shared and, on a 3 level page table, so could the mid level tables, but that's not a really big win because of the 1K/1 fanout. I.e, we already took care of 99.9% of the problem just by sharing the bottom-level page tables. > I'd have to look at it a bit more and do some noodling. > > > Confused yet? Welcome to the club ;-) > > Does my head exploding qualify for "confused"? If so, then I'm not > yet "confused". I'm "concerned", since my ears are bleeding (a > precursor to an explosion) ;-p :-) -- Daniel - 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/