From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <3DA5306C.7B63584@scs.ch> Date: Thu, 10 Oct 2002 09:46:52 +0200 From: Martin Maletinsky MIME-Version: 1.0 Subject: Meaning of the dirty bit Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: kernelnewbies@nl.linux.org, linux-mm@kvack.org List-ID: Hi, While studying the follow_page() function (the version of the function that is in place since 2.4.4, i.e. with the write argument), I noticed, that for an address that should be written to (i.e. write != 0), the function checks not only the writeable flag (with pte_write()), but also the dirty flag (with pte_dirty()) of the page containing this address. >>From what I thought to understand from general paging theory, the dirty flag of a page is set, when its content in physical memory differs from its backing on the permanent storage system (file or swap space). Based on this understanding I do not understand why it is necessary to check the dirty flag, in order to ensure that a page is writable - what am I missing here? Thanks in advance for any answers with best regards Martin Maletinsky P.S. Pls. put me on cc: in your reply, since I am not on the mailing list. -- Supercomputing System AG email: maletinsky@scs.ch Martin Maletinsky phone: +41 (0)1 445 16 05 Technoparkstrasse 1 fax: +41 (0)1 445 16 10 CH-8005 Zurich -- 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/