From owner-freebsd-fs@freebsd.org Sun Aug 21 08:28:53 2016 Return-Path: Delivered-To: freebsd-fs@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 57618BC076F for ; Sun, 21 Aug 2016 08:28:53 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id C762112E6 for ; Sun, 21 Aug 2016 08:28:52 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kib@localhost [127.0.0.1]) by kib.kiev.ua (8.15.2/8.15.2) with ESMTPS id u7L8ShiY047556 (version=TLSv1 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO); Sun, 21 Aug 2016 11:28:43 +0300 (EEST) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua u7L8ShiY047556 Received: (from kostik@localhost) by tom.home (8.15.2/8.15.2/Submit) id u7L8Sg0f047555; Sun, 21 Aug 2016 11:28:42 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Sun, 21 Aug 2016 11:28:42 +0300 From: Konstantin Belousov To: Karl Denninger Cc: freebsd-fs@freebsd.org Subject: Re: ZFS ARC under memory pressure Message-ID: <20160821082842.GR83214@kib.kiev.ua> References: <20160816193416.GM8192@zxy.spb.ru> <8dbf2a3a-da64-f7f8-5463-bfa23462446e@FreeBSD.org> <20160818202657.GS8192@zxy.spb.ru> <20160819201840.GA12519@zxy.spb.ru> <20160820152225.GP83214@kib.kiev.ua> <97f166f0-4d47-d5a3-ecb3-d15f1ecf9c1f@denninger.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <97f166f0-4d47-d5a3-ecb3-d15f1ecf9c1f@denninger.net> User-Agent: Mutt/1.6.1 (2016-04-27) X-Spam-Status: No, score=-2.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FREEMAIL_FROM,NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.1 X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on tom.home X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 21 Aug 2016 08:28:53 -0000 On Sat, Aug 20, 2016 at 11:08:44AM -0500, Karl Denninger wrote: > If you are talking about the case of an executable in which part of the > text is evicted you are correct, however, you are still choosing in that > instance to evict a page for which there will likely be a future demand > and thus require an I/O (should that executable come back up for > execution) as opposed to one for which you have no idea how likely > demand for same will be (a data page in the ARC.) No, I am not talking about only text segments. Any clean page can be reused after unmapping. > > Since the VM has no means of "coloring" the ARC (as it is opaque other > than the consumption of system memory to the VM) as to how "useful" > (e.g. how often used, etc) a particular data item in the ARC is, it has > no information available on which to decide. However, the fact that an > executing process is in some sort of waiting state still likely trumps > an ARC data page in terms of likelihood of future access. Buffer cache behaves exactly the same, since access references are not counted for the pages constituing buffers.