From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 4 Apr 2007 17:10:37 +0100 (BST) From: Hugh Dickins Subject: Re: [rfc] no ZERO_PAGE? In-Reply-To: <20070404154839.GI19587@v2.random> Message-ID: References: <20070329075805.GA6852@wotan.suse.de> <20070330024048.GG19407@wotan.suse.de> <20070404033726.GE18507@wotan.suse.de> <20070404154839.GI19587@v2.random> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Andrea Arcangeli Cc: Linus Torvalds , Nick Piggin , Andrew Morton , Linux Memory Management List , tee@sgi.com, holt@sgi.com, Linux Kernel Mailing List List-ID: On Wed, 4 Apr 2007, Andrea Arcangeli wrote: > On Wed, Apr 04, 2007 at 08:35:30AM -0700, Linus Torvalds wrote: > > Anyway, I'm not against this, but I can see somebody actually *wanting* > > the ZERO page in some cases. I've used the fact for TLB testing, for > > example, by just doing a big malloc(), and knowing that the kernel will > > re-use the ZERO_PAGE so that I don't get any cache effects (well, at least > > not any *physical* cache effects. Virtually indexed cached will still show > > effects of it, of course, but I haven't cared). > > Ok, those cases wanting the same zero page, could be fairly easily > converted to an mmap over /dev/zero No, MAP_SHARED mmap of /dev/zero uses shmem, which allocates distinct pages for this (because in general tmpfs doesn't know if a readonly file will be written to later on), and MAP_PRIVATE mmap of /dev/zero uses the zeromap stuff which we were hoping to eliminate too (though not in Nick's initial patch). Looks like a job for /dev/same_page_over_and_over_again. > (without having to run 4k large mmap syscalls or nonlinear). You scared me, I made no sense of that at first: ah yes, repeatedly mmap'ing the same page can be done those ways. Hugh -- 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: email@kvack.org