From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752932Ab0KOJFE (ORCPT ); Mon, 15 Nov 2010 04:05:04 -0500 Received: from mail-iw0-f174.google.com ([209.85.214.174]:47980 "EHLO mail-iw0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751547Ab0KOJFB convert rfc822-to-8bit (ORCPT ); Mon, 15 Nov 2010 04:05:01 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=DcdDSOBxVqetra4YHQOaZ78eeHNg9aHSSKGoSFdSgRGQzie7U4xhdPZ7LJuqyDzr4T iMeUU5hcxbfklfQaeg+vn4Bzv1XYe2p6Kdwx00kmptuyji6IEPwXUEu97mpu235gfR3P l5ZgTpy5MKPzSfW0DxrOoFp6h2Nu68XarYV+0= MIME-Version: 1.0 In-Reply-To: <1289810825.2109.469.camel@laptop> References: <20101109162525.BC87.A69D9226@jp.fujitsu.com> <877hgmr72o.fsf@gmail.com> <20101114140920.E013.A69D9226@jp.fujitsu.com> <1289810825.2109.469.camel@laptop> Date: Mon, 15 Nov 2010 18:05:00 +0900 Message-ID: Subject: Re: fadvise DONTNEED implementation (or lack thereof) From: Minchan Kim To: Peter Zijlstra Cc: KOSAKI Motohiro , Ben Gamari , linux-kernel@vger.kernel.org, rsync@lists.samba.org, linux-mm@kvack.org, Wu Fengguang , Rik van Riel Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 15, 2010 at 5:47 PM, Peter Zijlstra wrote: > On Mon, 2010-11-15 at 15:07 +0900, Minchan Kim wrote: >> On Sun, Nov 14, 2010 at 2:09 PM, KOSAKI Motohiro >> wrote: >> >> On Tue,  9 Nov 2010 16:28:02 +0900 (JST), KOSAKI Motohiro wrote: >> >> > So, I don't think application developers will use fadvise() aggressively >> >> > because we don't have a cross platform agreement of a fadvice behavior. >> >> > >> >> I strongly disagree. For a long time I have been trying to resolve >> >> interactivity issues caused by my rsync-based backup script. Many kernel >> >> developers have said that there is nothing the kernel can do without >> >> more information from user-space (e.g. cgroups, madvise). While cgroups >> >> help, the fix is round-about at best and requires configuration where >> >> really none should be necessary. The easiest solution for everyone >> >> involved would be for rsync to use FADV_DONTNEED. The behavior doesn't >> >> need to be perfectly consistent between platforms for the flag to be >> >> useful so long as each implementation does something sane to help >> >> use-once access patterns. >> >> >> >> People seem to mention frequently that there are no users of >> >> FADV_DONTNEED and therefore we don't need to implement it. It seems like >> >> this is ignoring an obvious catch-22. Currently rsync has no fadvise >> >> support at all, since using[1] the implemented hints to get the desired >> >> effect is far too complicated^M^M^M^Mhacky to be considered >> >> merge-worthy. Considering the number of Google hits returned for >> >> fadvise, I wouldn't be surprised if there were countless other projects >> >> with this same difficulty. We want to be able to tell the kernel about >> >> our useage patterns, but the kernel won't listen. >> > >> > Because we have an alternative solution already. please try memcgroup :) > > Using memcgroup for this is utter crap, it just contains the trainwreck, > it doesn't solve it in any way. > >> I think memcg could be a solution of them but fundamental solution is >> that we have to cure it in VM itself. >> I feel it's absolutely absurd to enable and use memcg for amending it. > > Agreed.. > >> I wonder what's the problem in Peter's patch 'drop behind'. >> http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg179576.html >> >> Could anyone tell me why it can't accept upstream? > > Read the thread, its quite clear nobody got convinced it was a good idea > and wanted to fix the use-once policy, then Rik rewrote all of > page-reclaim. > Thanks for the information. I hope this is a chance to rethink about it. Rik, Could you give us to any comment about this idea? -- Kind regards, Minchan Kim