From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: [PATCH] [13/21] Use blk_q_mask/get_pages_mask in sg driver Date: Mon, 17 Nov 2008 12:23:46 +0100 Message-ID: <20081117112346.GI6703@one.firstfloor.org> References: <20081116221722.GB6703@one.firstfloor.org> <20081117141240X.fujita.tomonori@lab.ntt.co.jp> <20081117102227.GG6703@one.firstfloor.org> <20081117200720M.fujita.tomonori@lab.ntt.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from one.firstfloor.org ([213.235.205.2]:52650 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751048AbYKQLOJ (ORCPT ); Mon, 17 Nov 2008 06:14:09 -0500 Content-Disposition: inline In-Reply-To: <20081117200720M.fujita.tomonori@lab.ntt.co.jp> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: FUJITA Tomonori Cc: andi@firstfloor.org, dgilbert@interlog.com, James.Bottomley@HansenPartnership.com, axboe@kernel.dk, linux-scsi@vger.kernel.org > > I would rather prefer to fix the driver to always GFP_DMA, but I am > > not aware of any driver who needs it. Are you? > > Well, theoretically, there migth be an user who want these ioctl with > all the drivers that are not capable of 64bit DMA since sg allocates > the reserved buffer with GFP_KERNEL. These driver might use the > block-layer bounce buffer. Users might want to use > SG_SET_FORCE_LOW_DMA to avoid the bounce buffer latency. But that would force everything through the 16MB zone, putting a lot of pressure on it and might even overflow on some loads. I don't think that's a good strategy for any application. -Andi -- ak@linux.intel.com