From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 22 Feb 2000 18:46:02 +0100 (MET) From: Richard Guenther Subject: mmap/munmap semantics Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Linux Kernel List Cc: glame-devel@lists.sourceforge.net, Linux-MM List-ID: Hi! With the ongoing development of GLAME there arise the following problems with the backing-store management, which is a mmaped file and does "userspace virtual memory management": - I cannot see a way to mmap a part of the file but set the contents initially to zero, i.e. I want to setup an initially dirty zero-mapping which is assigned to a part of the file. Currently I'm just mmaping the part and do the zeroing by reading from /dev/zero (which does as I understand from the kernel code just create this zero mappings) - is there a more portable way to achieve this? - I need to "drop" a mapping sometimes without writing the contents back to disk - I cannot see a way to do this with linux currently. Ideally a hole could be created in the mmapped file on drop time - is this possible at all with the VFS/ext2 at the moment (creating a hole in a file by dropping parts of it)? So for the first case we could add a flag to mmap like MAP_ZERO to indicate a zero-map (dirty). For the second case either the munmap call needs to be extended or some sort of madvise with a MADV_CLEAN flag? Or we can just adjust mprotect(PROT_NONE) and subsequent munmap() to do the dropping? Richard. -- The GLAME Project: http://www.glame.de/ Hosted by SourceForge: http://glame.sourceforge.net/ -- 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.eu.org/Linux-MM/