From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with SMTP id A50E06B01F9 for ; Mon, 26 Apr 2010 09:50:11 -0400 (EDT) Received: by pwi10 with SMTP id 10so2371685pwi.14 for ; Mon, 26 Apr 2010 06:50:07 -0700 (PDT) Message-ID: <4BD59956.7050508@vflare.org> Date: Mon, 26 Apr 2010 19:17:02 +0530 From: Nitin Gupta Reply-To: ngupta@vflare.org MIME-Version: 1.0 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> <4BD52D55.3070803@redhat.com> In-Reply-To: <4BD52D55.3070803@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Avi Kivity 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 List-ID: On 04/26/2010 11:36 AM, Avi Kivity wrote: > 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? > No, we cannot issue discard bio at this place since swap_lock spinlock is held. Thanks, Nitin -- 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