Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754222Ab0D0JWd (ORCPT ); Tue, 27 Apr 2010 05:22:33 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54345 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751451Ab0D0JWb (ORCPT ); Tue, 27 Apr 2010 05:22:31 -0400 Message-ID: <4BD6AC85.9000009@redhat.com> Date: Tue, 27 Apr 2010 12:21:09 +0300 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100330 Fedora/3.0.4-1.fc12 Thunderbird/3.0.4 MIME-Version: 1.0 To: Dan Magenheimer CC: ngupta@vflare.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, jeremy@goop.org, hugh.dickins@tiscali.co.uk, 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> <4BD24E37.30204@vflare.org> <4BD33822.2000604@redhat.com> <4BD3B2D1.8080203@vflare.org> <4BD4329A.9010509@redhat.com> <4BD4684E.9040802@vflare.org> <4BD52D55.3070803@redhat.com> <2634f2cb-3e7e-4c86-b7ef-cf4a3f1e0d8a@default 4BD5987F.7080505@redhat.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1768 Lines: 41 On 04/27/2010 11:29 AM, Dan Magenheimer wrote: > > OK, so on the one hand, you think that the proposed synchronous > interface for frontswap is insufficiently extensible for other > uses (presumably including KVM). On the other hand, you agree > that using the existing I/O subsystem is unnecessarily heavyweight. > On the third hand, Nitin has answered your questions and spent > a good part of three years finding that extending the existing swap > interface to efficiently support swap-to-pseudo-RAM requires > some kind of in-kernel notification mechanism to which Linus > has already objected. > > So you are instead proposing some new guest-to-host asynchronous > notification mechanism that doesn't use the existing bio > mechanism (and so presumably not irqs), (any notification mechanism has to use irqs if it exits the guest) > imitates or can > utilize a dma engine, and uses less cpu cycles than copying > pages. AND, for long-term maintainability, you'd like to avoid > creating a new guest-host API that does all this, even one that > is as simple and lightweight as the proposed frontswap hooks. > > Does that summarize your objection well? > No. Adding a new async API that parallels the block layer would be madness. My first preference would be to completely avoid new APIs. I think that would work for swap-to-hypervisor but probably not for compcache. Second preference is the synchronous API, third is a new async API. -- error compiling committee.c: too many arguments to function -- 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/