From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 40CDE6B00A2 for ; Wed, 6 May 2009 10:55:53 -0400 (EDT) Date: Wed, 6 May 2009 16:56:42 +0200 From: Andrea Arcangeli Subject: Re: [PATCH 2/6] ksm: dont allow overlap memory addresses registrations. Message-ID: <20090506145641.GA16078@random.random> References: <1241475935-21162-2-git-send-email-ieidus@redhat.com> <1241475935-21162-3-git-send-email-ieidus@redhat.com> <4A00DD4F.8010101@redhat.com> <4A015C69.7010600@redhat.com> <4A0181EA.3070600@redhat.com> <20090506131735.GW16078@random.random> <20090506140904.GY16078@random.random> <20090506152100.41266e4c@lxorguk.ukuu.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org To: Hugh Dickins Cc: Alan Cox , Rik van Riel , Izik Eidus , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, chrisw@redhat.com, device@lanana.org, linux-mm@kvack.org, nickpiggin@yahoo.com.au List-ID: On Wed, May 06, 2009 at 03:46:31PM +0100, Hugh Dickins wrote: > As I understand it, KSM won't affect the vm_overcommit behaviour at all. In short vm_overcommit is a virtual thing, KSM only makes virtual takes less physical than before. One issue in KSM that was mentioned was the cgroup accounting if you merge two pages in different groups but that is kind of a corner case and it'll be handled "somehow" :) > The only difference would be in how much memory (mostly lowmem) > KSM's own data structures will take up - as usual, the kernel > data structures aren't being accounted, but do take up memory. Oh yeah, on 32bit systems that would be a problem... That lowmem is taken for eacy virtual address scanned. One more reason to still allow ksm to all users only selectively through chown/chmod with ioctl or sysfs permissions with syscall/madvise. Luckily most systems where ksm is used are 64bit. We don't plan to kmap_atomic around the rmap_item/tree_item. No ram is allocated in the holes though, so if there's not a real anonymous page allocated the rmap_item will not be allocated either (without requiring pending update ;). -- 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