Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753496Ab0DZGGh (ORCPT ); Mon, 26 Apr 2010 02:06:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59572 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752076Ab0DZGGg (ORCPT ); Mon, 26 Apr 2010 02:06:36 -0400 Message-ID: <4BD52D55.3070803@redhat.com> Date: Mon, 26 Apr 2010 09:06:13 +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: ngupta@vflare.org CC: Dan Magenheimer , 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> <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> In-Reply-To: <4BD4684E.9040802@vflare.org> 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: 1947 Lines: 55 On 04/25/2010 07:05 PM, Nitin Gupta wrote: > >>> Increasing the frequency of discards is also not an option: >>> - Creating discard bio requests themselves need memory and these >>> swap devices >>> come into picture only under low memory conditions. >>> >>> >> That's fine, swap works under low memory conditions by using reserves. >> >> > Ok, but still all this bio allocation and block layer overhead seems > unnecessary and is easily avoidable. I think frontswap code needs > clean up but at least it avoids all this bio overhead. > Ok. I agree it is silly to go through the block layer and end up servicing it within the kernel. >>> - We need to regularly scan swap_map to issue these discards. >>> Increasing discard >>> frequency also means more frequent scanning (which will still not be >>> fast enough >>> for ramzswap needs). >>> >>> >> How does frontswap do this? Does it maintain its own data structures? >> >> > frontswap simply calls frontswap_flush_page() in swap_entry_free() i.e. as > soon as a swap slot is freed. No bio allocation etc. > The same code could also issue the discard? >> Even for copying to RAM an async API is wanted, so you can dma it >> instead of copying. >> >> > Maybe incremental development is better? Stabilize and refine existing > code and gradually move to async API, if required in future? > Incremental development is fine, especially for ramzswap where the APIs are all internal. I'm more worried about external interfaces, these stick around a lot longer and if not done right they're a pain forever. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. -- 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/