Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934982AbaKNBYF (ORCPT ); Thu, 13 Nov 2014 20:24:05 -0500 Received: from smtp.codeaurora.org ([198.145.11.231]:32960 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934699AbaKNBYD (ORCPT ); Thu, 13 Nov 2014 20:24:03 -0500 Message-ID: <546559B2.4090003@codeaurora.org> Date: Thu, 13 Nov 2014 17:24:02 -0800 From: Laura Abbott User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 To: Gioh Kim , Colin Cross , Joonsoo Kim CC: John Stultz , Greg Kroah-Hartman , devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org, =?EUC-KR?B?IsDMsMfIoy/DpcDTv6yxuL/4L1NXIFBsYXRmb3JtKL+sKUFPVMbAKGd1bmhvLg==?= =?EUC-KR?B?bGVlQGxnZS5jb20pIg==?= Subject: Re: Why does ion_cma_allocate need GFP_HIGHUSER | __GFP_ZERO flags? References: <54645B38.10603@lge.com> In-Reply-To: <54645B38.10603@lge.com> Content-Type: text/plain; charset=euc-kr Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/12/2014 11:18 PM, Gioh Kim wrote: > Hi, > > I'm wondering why dma_alloc_coherent needs GFP_HIGHUSER | __GFP_ZERO flags in ion_cma_allocate(). > > I think dma_alloc_coherent can go to __dma_alloc if the system has CMA area. > If __GFP_WAIT flag is set, it allocates memory from atomic pool. > So I think calling dma_alloc_coherent with __GFP_WAIT is enough. > > And can I get zero-filled-memory from CMA if I set __GFP_ZERO? > > If we are actually using CMA, the GFP flags don't make much of a difference. If we didn't have CMA, using GFP_HIGHUSER would still be appropriate. The memory is going to userspace so the user part is necessary and there should be no need for a lowmem mapping so highmem can be used. __GFP_ZERO might be redundant since the dma layer zeros memory anyway but it's probably safe. I think the flags should be fine as is. Thanks, Laura -- Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project -- 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/