From owner-freebsd-fs@FreeBSD.ORG Wed Feb 15 16:06:35 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 510C71065670 for ; Wed, 15 Feb 2012 16:06:35 +0000 (UTC) (envelope-from gkontos.mail@gmail.com) Received: from mail-iy0-f182.google.com (mail-iy0-f182.google.com [209.85.210.182]) by mx1.freebsd.org (Postfix) with ESMTP id 1C32E8FC0A for ; Wed, 15 Feb 2012 16:06:34 +0000 (UTC) Received: by iaeo4 with SMTP id o4so2109159iae.13 for ; Wed, 15 Feb 2012 08:06:34 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=Y8M6FJjZz2kGsf0IY3gi0l5F/irHIFjd7j/sooxiYd4=; b=Dr3O9OQBrPr6oCOUvzCRCCX3NBIM8S/1ByUjyxPxgb7TaFtXXFd4/s18/ChgX1nDCq 8k6bmosvtJhgt47Q9NP6V50LQAIXP+S44DvYLT4xB+M1u4JECT2MNXttzTg3iJA+dGlg eEusBY33DZir2XK1f6UOK2rny6PQNBQc6K+G0= MIME-Version: 1.0 Received: by 10.42.138.193 with SMTP id d1mr34537549icu.0.1329321994522; Wed, 15 Feb 2012 08:06:34 -0800 (PST) Received: by 10.231.231.17 with HTTP; Wed, 15 Feb 2012 08:06:34 -0800 (PST) In-Reply-To: <4633.1329320658.10597993752278204416@ffe16.ukr.net> References: <41082.1329320114.6955040073494560768@ffe1.ukr.net> <70229.1329318412.9319724204137054208@ffe16.ukr.net> <4633.1329320658.10597993752278204416@ffe16.ukr.net> Date: Wed, 15 Feb 2012 18:06:34 +0200 Message-ID: From: George Kontostanos To: Pavlo Content-Type: text/plain; charset=ISO-8859-1 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 16:06:35 -0000 2012/2/15 Pavlo : > > > --- 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 ltd > http://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. > I guess then that a memory upgrade should be scheduled. -- George Kontostanos Aicom telecoms ltd http://www.aisecure.net