From owner-freebsd-fs@FreeBSD.ORG Wed Feb 15 15:44:19 2012 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id B91C01065679 for ; Wed, 15 Feb 2012 15:44:19 +0000 (UTC) (envelope-from devgs@ukr.net) Received: from ffe16.ukr.net (ffe16.ukr.net [195.214.192.51]) by mx1.freebsd.org (Postfix) with ESMTP id 46FA18FC14 for ; Wed, 15 Feb 2012 15:44:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=ukr.net; s=ffe; h=Date:Message-Id:From:To:References:In-Reply-To:Subject:Cc:Content-Type:Content-Transfer-Encoding:MIME-Version; bh=5XPzh5pRot8Rh7B0OHK9x6pnz/2UeL8q6UksFyAIfsY=; b=FCdkzkuSGn5mSqSbZJF1giLSaWAGHKGYpHbWPkj/Bi5fwOqlja4WlZdF/AlCJ2gAR4yuJzaeWMkTyx+gKJWwbUu1pvm0aCR4BGyXb8si2D5YwTRDuo1lvaZ4efdRyzIhqrM25VggT/YiDZhVJ5ocRy41Y+2MxPCvk7PLoBGy91I=; Received: from mail by ffe16.ukr.net with local ID 1Rxh1m-0001IR-5m ; Wed, 15 Feb 2012 17:44:18 +0200 MIME-Version: 1.0 In-Reply-To: References: <41082.1329320114.6955040073494560768@ffe1.ukr.net> <70229.1329318412.9319724204137054208@ffe16.ukr.net> To: "George Kontostanos" From: "Pavlo" X-Mailer: freemail.ukr.net 4.0 X-Originating-Ip: [212.42.94.154] Message-Id: <4633.1329320658.10597993752278204416@ffe16.ukr.net> X-Browser: Mozilla/5.0 (X11; Ubuntu; Linux i686; rv:10.0.1) Gecko/20100101 Firefox/10.0.1 Date: Wed, 15 Feb 2012 17:44:18 +0200 Content-Type: text/plain; charset="windows-1251" Content-Transfer-Encoding: binary Content-Disposition: inline X-Content-Filtered-By: Mailman/MimeDel 2.1.5 Cc: freebsd-fs@freebsd.org Subject: Re: ZFS and mem management X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 15 Feb 2012 15:44:19 -0000 --- Original message --- From: "George Kontostanos" To: "Pavlo" Date: 15 February 2012, 17:39:46 Subject: Re: ZFS and mem management > 2012/2/15 Pavlo : > > > 2012/2/15 Pavlo : >> >> >> >>>On 15/02/2012 13:39, Pavlo wrote: >>>> >> >>>> >> >> Unfortunately we can't afford disabling prefetch. It is too much >>>> >> >> of an>> overhead.>> >> Also I made some tests. I have process that maps file >>>> >> >> using mmap() and>> writes or reads first byte of each page of mapped file >>>> >> >> with some data.> >>>Note that ZFS is designed so that it interacts somewhat badly with >>>mmap() and other kernel services which rely on coherency between VM and >>>IO such as sendfile(). At the very best, you will have two in-kernel >>>copies of all data buffers used with such interfaces, but there have >>>been sporadic reports that there are other bugs with it. >>> >>>If you have a test server, I'd recommend you do the same test on UFS for >>>comparison. >> >> Was going to try this... Thanks for reply. >> _______________________________________________ >> freebsd-fs@freebsd.org mailing list >> http://lists.freebsd.org/mailman/listinfo/freebsd-fs>> To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org" > > Why do you think that disabling prefetch is an overhead? > > > -- > George Kontostanos > Aicom telecoms ltd > http://www.aisecure.net> > > > Well... not me though. System administrator >_> . I suppose because we have > a big IO traffic. Not for a highly random I/O environment. -- George Kontostanos Aicom telecoms ltdhttp://www.aisecure.net > That's is a reason we don't disable. Our reads and writes mostly contiguous. And that problem arises on machines with low RAM (8Gb and less). Also for obvious reasons swap is disabled.