Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756275AbYGPSD2 (ORCPT ); Wed, 16 Jul 2008 14:03:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752573AbYGPSDR (ORCPT ); Wed, 16 Jul 2008 14:03:17 -0400 Received: from mx1.redhat.com ([66.187.233.31]:33262 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751763AbYGPSDQ (ORCPT ); Wed, 16 Jul 2008 14:03:16 -0400 Date: Wed, 16 Jul 2008 14:02:27 -0400 (EDT) From: Mikulas Patocka X-X-Sender: mpatocka@devserv.devel.redhat.com To: FUJITA Tomonori cc: jens.axboe@oracle.com, linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, davem@davemloft.net, linux-parisc@vger.kernel.org Subject: Re: [PATCH] block: fix q->max_segment_size checking in blk_recalc_rq_segments about VMERGE In-Reply-To: <20080716093456J.fujita.tomonori@lab.ntt.co.jp> Message-ID: References: <20080716003047P.fujita.tomonori@lab.ntt.co.jp> <20080716093456J.fujita.tomonori@lab.ntt.co.jp> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1566 Lines: 39 On Wed, 16 Jul 2008, FUJITA Tomonori wrote: > On Tue, 15 Jul 2008 11:46:46 -0400 (EDT) > Mikulas Patocka wrote: > > > >> Even if we fix it now, the question is: how long it will stay fixed? Until > > >> someone makes another change to struct device that restricts boundaries on > > >> some wacky hardware. > > > > > > I'm not sure how the boundary restriction of a device can break > > > the VMERGE accounting. > > > > Because block layer code doesn't know anything about the device, pci > > access restrictions and so on. > > Not true, the block layer knows about the device restrictions like DMA > boundary. > > But it's not the point here because the boundary restriction doesn't > matter for the VMERGE accounting. An IOMMU just returns an error if it > can't allocate an I/O space fit for the device restrictions. > > > Please give me an example how the boundary restriction of a device can > break the VMERGE accounting and an IOMMU if you aren't still sure. You have dma_get_seg_boundary and dma_get_max_seg_size. On sparc64, adding one of these broken VMERGE accounting (the VMERGE didn't happen past 64-kb boundary and bio layer thought that VMERGE would be possible). And if you fix this case, someone will break it again, sooner or later, by adding new restriction. Mikulas -- 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/