Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933433Ab3HGVMp (ORCPT ); Wed, 7 Aug 2013 17:12:45 -0400 Received: from server506b.appriver.com ([50.56.144.14]:51367 "EHLO server506.appriver.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S933227Ab3HGVMk convert rfc822-to-8bit (ORCPT ); Wed, 7 Aug 2013 17:12:40 -0400 X-Note-AR-ScanTimeLocal: 8/7/2013 4:12:38 PM X-Policy: GLOBAL - coraid.com X-Policy: GLOBAL - coraid.com X-Policy: GLOBAL - coraid.com X-Primary: ecashin@coraid.com X-Note: This Email was scanned by AppRiver SecureTide X-Virus-Scan: V- X-Note-SnifferID: 0 X-Note: TCH-CT/SI:0-82/SG:2 8/7/2013 4:12:37 PM X-GBUdb-Analysis: 0, 10.242.229.139, Ugly c=1 p=-0.977602 Source White X-Signature-Violations: 0-0-0-4229-c X-Note-419: 15.6008 ms. Fail:0 Chk:1343 of 1343 total X-Note: SCH-CT/SI:0-1343/SG:1 8/7/2013 4:12:19 PM X-Note: Spam Tests Failed: X-Country-Path: PRIVATE->PRIVATE->UNITED STATES X-Note-Sending-IP: 10.242.229.139 X-Note-Reverse-DNS: X-Note-Return-Path: ecashin@coraid.com X-Note: User Rule Hits: X-Note: Global Rule Hits: G319 G320 G321 G322 G326 G327 G434 X-Note: Encrypt Rule Hits: X-Note: Mail Class: VALID X-Note: Headers Injected Subject: Re: [PATCH] aoe: adjust ref of head for compound page tails MIME-Version: 1.0 (Apple Message framework v1085) Content-Type: text/plain; charset="us-ascii" From: Ed Cashin In-Reply-To: <20130807135804.e62b75f6986e9568ab787562@linux-foundation.org> Date: Wed, 7 Aug 2013 17:12:36 -0400 CC: , Christoph Hellwig Content-Transfer-Encoding: 8BIT Message-ID: <8DFEA276-4EE1-44B4-9669-5634631D7BBC@coraid.com> References: <0c8aff39249c1da6b9cc3356650149d065c3ebd2.1375320764.git.ecashin@coraid.com> <20130807135804.e62b75f6986e9568ab787562@linux-foundation.org> To: Andrew Morton X-Mailer: Apple Mail (2.1085) X-Rerouted-By-Exchange: X-Rerouted-By-Exchange: X-Rerouted-By-Exchange: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1728 Lines: 40 On Aug 7, 2013, at 4:58 PM, Andrew Morton wrote: > On Thu, 1 Aug 2013 21:29:59 -0400 Ed Cashin wrote: > >> As discussed previously, > > I think I missed that. > >> the fact that some users of the block >> layer provide bios that point to pages with a zero _count means >> that it is not OK for the network layer to do a put_page on the >> skb frags during an skb_linearize, so the aoe driver gets a >> reference to pages in bios and puts the reference before ending >> the bio. And because it cannot use get_page on a page with a >> zero _count, it manipulates the value directly. > > Eh? What code is putting count==0 pages into bios? That sounds very > weird and broken. I thought so in 2007 but couldn't solicit a clear "this is wrong" consensus from the discussion. http://article.gmane.org/gmane.linux.kernel/499197 https://lkml.org/lkml/2007/1/19/56 https://lkml.org/lkml/2006/12/18/230 We were seeing zero-count pages in bios from XFS, but Christoph Hellwig pointed out that kmalloced pages can also come from ext3 when it's doing log recovery, and they'll have zero page counts. I don't have a counter in the driver to track how often zero-count pages show up in bios, so I don't know how common it is these days. I would have been motivated to look if I had gotten the impression that there was any interest in identifying and eliminating cases where zero-count pages were being used in bios. -- Ed Cashin ecashin@coraid.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/