From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id 1ED366B00A2 for ; Wed, 6 May 2009 10:46:03 -0400 (EDT) Date: Wed, 6 May 2009 15:46:31 +0100 (BST) From: Hugh Dickins Subject: Re: [PATCH 2/6] ksm: dont allow overlap memory addresses registrations. In-Reply-To: <20090506152100.41266e4c@lxorguk.ukuu.org.uk> Message-ID: References: <1241475935-21162-1-git-send-email-ieidus@redhat.com> <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 Sender: owner-linux-mm@kvack.org To: Alan Cox Cc: Andrea Arcangeli , 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, 6 May 2009, Alan Cox wrote: > > the max number of ksm pages that can be allocated at any given time so > > to avoid OOM conditions, like the swap-compress logic that limits the > > swapdevice size to less than ram. (I don't know anything about that swap-compress logic and limitation.) > > Are those pages accounted for in the vm_overcommit logic, as if you > allocate a big chunk of memory as KSM will do you need the worst case > vm_overcommit behaviour preserved and that means keeping the stats > correct. As I understand it, KSM won't affect the vm_overcommit behaviour at all. Those pages Izik refers to are not allocated up front, they're just a limit on the number of process pages which may get held in core at any one time, through being shared via the KSM mechanism. KSM is not evading vm_committed_space at all, not opening a backdoor away from the ordinary mmaps: just collapsing duplicated pages in what's been mapped in the usual way, down to single copies. So the vm_commited_space accounting is exactly as before: it would be a bit odd to be running KSM along with OVERCOMMIT_NEVER, but it doesn't change its calculations at all - it will and will have to be as pessimistic as it ever was. 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. 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