From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752702Ab0KOIq4 (ORCPT ); Mon, 15 Nov 2010 03:46:56 -0500 Received: from casper.infradead.org ([85.118.1.10]:56894 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751023Ab0KOIqz convert rfc822-to-8bit (ORCPT ); Mon, 15 Nov 2010 03:46:55 -0500 Subject: Re: fadvise DONTNEED implementation (or lack thereof) From: Peter Zijlstra To: Minchan Kim Cc: KOSAKI Motohiro , Ben Gamari , linux-kernel@vger.kernel.org, rsync@lists.samba.org, linux-mm@kvack.org, Wu Fengguang In-Reply-To: References: <20101109162525.BC87.A69D9226@jp.fujitsu.com> <877hgmr72o.fsf@gmail.com> <20101114140920.E013.A69D9226@jp.fujitsu.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Mon, 15 Nov 2010 09:47:05 +0100 Message-ID: <1289810825.2109.469.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.