From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with ESMTP id 3B5386B013E for ; Wed, 13 May 2009 19:17:26 -0400 (EDT) Date: Wed, 13 May 2009 16:17:39 -0700 From: Andrew Morton Subject: Re: [PATCH 5/5] add ksm kernel shared memory driver. Message-Id: <20090513161739.d801ab67.akpm@linux-foundation.org> In-Reply-To: <1240191366-10029-6-git-send-email-ieidus@redhat.com> References: <1240191366-10029-1-git-send-email-ieidus@redhat.com> <1240191366-10029-2-git-send-email-ieidus@redhat.com> <1240191366-10029-3-git-send-email-ieidus@redhat.com> <1240191366-10029-4-git-send-email-ieidus@redhat.com> <1240191366-10029-5-git-send-email-ieidus@redhat.com> <1240191366-10029-6-git-send-email-ieidus@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Izik Eidus Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, kvm@vger.kernel.org, avi@redhat.com, aarcange@redhat.com, chrisw@redhat.com, mtosatti@redhat.com, hugh@veritas.com List-ID: On Mon, 20 Apr 2009 04:36:06 +0300 Izik Eidus wrote: > Ksm is driver that allow merging identical pages between one or more > applications in way unvisible to the application that use it. > Pages that are merged are marked as readonly and are COWed when any > application try to change them. > > Ksm is used for cases where using fork() is not suitable, > one of this cases is where the pages of the application keep changing > dynamicly and the application cannot know in advance what pages are > going to be identical. > > Ksm works by walking over the memory pages of the applications it > scan in order to find identical pages. > It uses a two sorted data strctures called stable and unstable trees > to find in effective way the identical pages. > > When ksm finds two identical pages, it marks them as readonly and merges > them into single one page, > after the pages are marked as readonly and merged into one page, linux > will treat this pages as normal copy_on_write pages and will fork them > when write access will happen to them. > > Ksm scan just memory areas that were registred to be scanned by it. > > ... > + copy_user_highpage(kpage, page1, addr1, vma); > ... Breaks ppc64 allmodcofnig because that architecture doesn't export its copy_user_page() to modules. Architectures are inconsistent about this. x86 _does_ export it, because it bounces it to the exported copy_page(). So can I ask that you sit down and work out upon which architectures it really makes sense to offer KSM? Disallow the others in Kconfig and arrange for copy_user_highpage() to be available on the allowed architectures? Thanks. -- 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