From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: follow_page() From: Arjan van de Ven In-Reply-To: <20041111024015.7c50c13d.akpm@osdl.org> References: <20041111024015.7c50c13d.akpm@osdl.org> Content-Type: text/plain Message-Id: <1100170570.2646.27.camel@laptop.fenrus.org> Mime-Version: 1.0 Date: Thu, 11 Nov 2004 11:56:10 +0100 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: linux-mm@kvack.org List-ID: On Thu, 2004-11-11 at 02:40 -0800, Andrew Morton wrote: > Can anyone think of a sane reason why this thing is marking the page dirty? > > I mean, we're supposed to mark the page dirty _after_ modifying its > contents. most likely it's because the intent to write to it is given. It's cheaper for the OS to mark a pagetable dirty than it's for the CPU to do so (example, on a Pentium 4 it can easily take the cpu 2000 to 4000 cycles to flip the dirty bit on the PTE). So if you KNOW you're going to write to it (and thus the intent parameter) you can save a big chunk of those cycles. -- -- 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: aart@kvack.org