From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752610AbaIGVBG (ORCPT ); Sun, 7 Sep 2014 17:01:06 -0400 Received: from mail1.SerNet.de ([193.175.80.2]:37383 "EHLO mail.SerNet.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752114AbaIGVBF (ORCPT ); Sun, 7 Sep 2014 17:01:05 -0400 X-Greylist: delayed 708 seconds by postgrey-1.27 at vger.kernel.org; Sun, 07 Sep 2014 17:01:04 EDT Date: Sun, 7 Sep 2014 22:48:51 +0200 From: Volker Lendecke To: Milosz Tanski Cc: Christoph Hellwig , Mel Gorman , LKML , Tejun Heo , linux-aio@kvack.org Subject: Re: read()/readv() only from page cache Reply-To: Volker.Lendecke@SerNet.DE References: <20140905110927.GI17501@suse.de> <20140905154829.GA22956@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Message-Id: Organization: SerNet GmbH, Goettingen, Germany Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 05, 2014 at 12:27:21PM -0400, Milosz Tanski wrote: > In a VLDB like workload this would enable me to lower the latency of > common fast requests and. By fast requests I mean ones that do not > require much data, the data is cached, or there's a predictable read > pattern (read-ahead). Obviously it would be at the expense of the > latency of large/slow requests (they have to make 2 read calls, the > first one always EWOULDBLOCK) ... but in that case it doesn't matter > since the time to do actual IO would trump any kind of extra latency. That was my thinking as well when I discussed it with Christoph. Sorry for not getting around to actually test his patch. Samba right now uses a thread pool for aio, we get parallel read requests from clients over a single TCP connection and we need to keep all disks busy simultaneously. We'd like to avoid the thread overhead when it's not necessary because the data is already around. A per-request flag would fit Samba better than a flag settable by fcntl in this pattern. Samba can't easily open a file twice (once with NONBLOCK and once without). Volker -- SerNet GmbH, Bahnhofsallee 1b, 37081 Göttingen phone: +49-551-370000-0, fax: +49-551-370000-9 AG Göttingen, HRB 2816, GF: Dr. Johannes Loxen http://www.sernet.de, mailto:kontakt@sernet.de