Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754251Ab0DYAl6 (ORCPT ); Sat, 24 Apr 2010 20:41:58 -0400 Received: from rcsinet10.oracle.com ([148.87.113.121]:23754 "EHLO rcsinet10.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752721Ab0DYAl5 convert rfc822-to-8bit (ORCPT ); Sat, 24 Apr 2010 20:41:57 -0400 MIME-Version: 1.0 Message-ID: <1c02a94a-a6aa-4cbb-a2e6-9d4647760e91@default> Date: Sat, 24 Apr 2010 17:41:04 -0700 (PDT) From: Dan Magenheimer To: Avi Kivity Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, jeremy@goop.org, hugh.dickins@tiscali.co.uk, ngupta@vflare.org, JBeulich@novell.com, chris.mason@oracle.com, kurt.hackel@oracle.com, dave.mccracken@oracle.com, npiggin@suse.de, akpm@linux-foundation.org, riel@redhat.com Subject: RE: Frontswap [PATCH 0/4] (was Transcendent Memory): overview References: <20100422134249.GA2963@ca-server1.us.oracle.com> <4BD06B31.9050306@redhat.com> <53c81c97-b30f-4081-91a1-7cef1879c6fa@default> <4BD07594.9080905@redhat.com> <4BD16D09.2030803@redhat.com> <4BD1A74A.2050003@redhat.com> <4830bd20-77b7-46c8-994b-8b4fa9a79d27@default> <4BD1B427.9010905@redhat.com> <4BD1B626.7020702@redhat.com> <5fa93086-b0d7-4603-bdeb-1d6bfca0cd08@default 4BD3377E.6010303@redhat.com> In-Reply-To: <4BD3377E.6010303@redhat.com> X-Priority: 3 X-Mailer: Oracle Beehive Extensions for Outlook 1.5.1.5.2 (401224) [OL 12.0.6514.5000] Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-Auth-Type: Internal IP X-Source-IP: acsinet15.oracle.com [141.146.126.227] X-CT-RefId: str=0001.0A090202.4BD38FBA.001E:SCFMA922111,ss=1,fgs=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1316 Lines: 25 > > No, ANY put_page can fail, and this is a critical part of the API > > that provides all of the flexibility for the hypervisor and all > > the guests. (See previous reply.) > > The guest isn't required to do any put_page()s. It can issue lots of > them when memory is available, and keep them in the hypervisor forever. > Failing new put_page()s isn't enough for a dynamic system, you need to > be able to force the guest to give up some of its tmem. Yes, indeed, this is true. That is why it is important for any policy implemented behind frontswap to "bill" the guest if it is attempting to keep frontswap pages in the hypervisor forever and to prod the guest to reclaim them when it no longer needs super-fast emergency swap space. The frontswap patch already includes the kernel mechanism to enable this and the prodding can be implemented by a guest daemon (of which there already exists an existence proof). (While devil's advocacy is always welcome, frontswap is NOT a cool academic science project where these issues have not been considered or tested.) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/