Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753532AbaFXOPR (ORCPT ); Tue, 24 Jun 2014 10:15:17 -0400 Received: from fw-tnat.austin.arm.com ([217.140.110.23]:25461 "EHLO collaborate-mta1.arm.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752322AbaFXOPM (ORCPT ); Tue, 24 Jun 2014 10:15:12 -0400 Date: Tue, 24 Jun 2014 15:14:55 +0100 From: Catalin Marinas To: Mark Salter Cc: Will Deacon , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] arm64: make CONFIG_ZONE_DMA user settable Message-ID: <20140624141455.GE4489@arm.com> References: <1403499924-11214-1-git-send-email-msalter@redhat.com> <20140623110937.GB15907@arm.com> <1403529423.755.49.camel@deneb.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1403529423.755.49.camel@deneb.redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 23, 2014 at 02:17:03PM +0100, Mark Salter wrote: > On Mon, 2014-06-23 at 12:09 +0100, Catalin Marinas wrote: > > My proposal (in the absence of any kind of description) is to still > > create a ZONE_DMA if we have DMA memory below 32-bit, otherwise just add > > everything (>32-bit) to ZONE_DMA. Basically an extension from your CMA > > patch, make dma_phys_limit static in that file and set it to > > memblock_end_of_DRAM() if no 32-bit DMA. Re-use it in the > > zone_sizes_init() function for ZONE_DMA (maybe with a pr_info for no > > 32-bit only DMA zone). > > There's a performance issue with all memory being in ZONE_DMA. It means > all normal allocations will fail on ZONE_NORMAL and then have to fall > back to ZONE_DMA. It would be better to put some percentage of memory > in ZONE_DMA. Is the performance penalty real or just theoretical? I haven't run any benchmarks myself. -- Catalin -- 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/