From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4D89FC43382 for ; Fri, 28 Sep 2018 00:08:56 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id BA2882172C for ; Fri, 28 Sep 2018 00:08:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BA2882172C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 42LsTx53FXzF39K for ; Fri, 28 Sep 2018 10:08:53 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: lists.ozlabs.org; spf=permerror (mailfrom) smtp.mailfrom=kernel.crashing.org (client-ip=63.228.1.57; helo=gate.crashing.org; envelope-from=benh@kernel.crashing.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 42LsRs14s0zF38s for ; Fri, 28 Sep 2018 10:07:04 +1000 (AEST) Received: from localhost (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id w8S06mRi025169; Thu, 27 Sep 2018 19:06:49 -0500 Message-ID: <514bd29960cb1573ead2f3956f18e1cbaa5f32f7.camel@kernel.crashing.org> Subject: Re: [PATCH 3/5] dma-direct: refine dma_direct_alloc zone selection From: Benjamin Herrenschmidt To: Christoph Hellwig Date: Fri, 28 Sep 2018 10:06:48 +1000 In-Reply-To: <20180927134922.GA8281@lst.de> References: <20180920185247.20037-1-hch@lst.de> <20180920185247.20037-4-hch@lst.de> <1811156d5a1df1166c7ab7522525619b951f047d.camel@kernel.crashing.org> <20180927134922.GA8281@lst.de> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5 (3.28.5-1.fc28) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Greg Kroah-Hartman , Robin Murphy , linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, linuxppc-dev@lists.ozlabs.org, Marek Szyprowski Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Thu, 2018-09-27 at 15:49 +0200, Christoph Hellwig wrote: > On Thu, Sep 27, 2018 at 11:45:15AM +1000, Benjamin Herrenschmidt wrote: > > I'm not sure this is entirely right. > > > > Let's say the mask is 30 bits. You will return GFP_DMA32, which will > > fail if you allocate something above 1G (which is legit for > > ZONE_DMA32). > > And then we will try GFP_DMA further down in the function: > > if (IS_ENABLED(CONFIG_ZONE_DMA) && > dev->coherent_dma_mask < DMA_BIT_MASK(32) && > !(gfp & GFP_DMA)) { > gfp = (gfp & ~GFP_DMA32) | GFP_DMA; > goto again; > } > > This is and old optimization from x86, because chances are high that > GFP_DMA32 will give you suitable memory for the infamous 31-bit > dma mask devices (at least at boot time) and thus we don't have > to deplete the tiny ZONE_DMA pool. I see, it's rather confusing :-) Wouldn't it be better to check against top of 32-bit memory instead here too ? Cheers, Ben.