From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753269Ab0KIIDP (ORCPT ); Tue, 9 Nov 2010 03:03:15 -0500 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:43671 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753082Ab0KIIDN (ORCPT ); Tue, 9 Nov 2010 03:03:13 -0500 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 From: KOSAKI Motohiro To: KOSAKI Motohiro Subject: Re: fadvise DONTNEED implementation (or lack thereof) Cc: kosaki.motohiro@jp.fujitsu.com, Ben Gamari , linux-kernel@vger.kernel.org, rsync@lists.samba.org, linux-mm@kvack.org In-Reply-To: <20101109162525.BC87.A69D9226@jp.fujitsu.com> References: <87lj597hp9.fsf@gmail.com> <20101109162525.BC87.A69D9226@jp.fujitsu.com> Message-Id: <20101109170303.BC90.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.50.07 [ja] Date: Tue, 9 Nov 2010 17:03:09 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > I've recently been trying to track down the root cause of my server's > > persistent issue of thrashing horribly after being left inactive. It > > seems that the issue is likely my nightly backup schedule (using rsync) > > which traverses my entire 50GB home directory. I was surprised to find > > that rsync does not use fadvise to notify the kernel of its use-once > > data usage pattern. > > > > It looks like a patch[1] was written (although never merged, it seems) > > incorporating fadvise support, but I found its implementation rather > > odd, using mincore() and FADV_DONTNEED to kick out only regions brought > > in by rsync. It seemed to me the simpler and more appropriate solution > > would be to simply flag every touched file with FADV_NOREUSE and let the > > kernel manage automatically expelling used pages. > > > > After looking deeper into the kernel implementation[2] of fadvise() the > > reason for using DONTNEED became more apparant. It seems that the kernel > > implements NOREUSE as a noop. A little googling revealed[3] that I not > > the first person to encounter this limitation. It looks like a few > > folks[4] have discussed addressing the issue in the past, but nothing > > has happened as of 2.6.36. Are there plans to implement this > > functionality in the near future? It seems like the utility of fadvise > > is severely limited by lacking support for NOREUSE. > > btw, Other OSs seems to also don't implement it. > example, I've heared other OSs status of fadvise() from private mail. NetBSD: no-op (as linux) FreeBSD/DragonflyBSD/OpenBSD: don't exist posix_fadvise(2)