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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham 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 9F55DC07E85 for ; Fri, 7 Dec 2018 07:25:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6A85D208E7 for ; Fri, 7 Dec 2018 07:25:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6A85D208E7 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726015AbeLGHZe (ORCPT ); Fri, 7 Dec 2018 02:25:34 -0500 Received: from mx2.suse.de ([195.135.220.15]:34004 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725948AbeLGHZd (ORCPT ); Fri, 7 Dec 2018 02:25:33 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 9CE7FAF0C; Fri, 7 Dec 2018 07:25:31 +0000 (UTC) Subject: Re: [PATCH v5 1/3] mm: Add support for kmem caches in DMA32 zone To: Nicolas Boichat , Will Deacon Cc: Robin Murphy , Joerg Roedel , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Michal Hocko , Mel Gorman , Levin Alexander , Huaisheng Ye , Mike Rapoport , linux-arm-kernel@lists.infradead.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Yong Wu , Matthias Brugger , Tomasz Figa , yingjoe.chen@mediatek.com, hch@infradead.org, Matthew Wilcox References: <20181207061620.107881-1-drinkcat@chromium.org> <20181207061620.107881-2-drinkcat@chromium.org> From: Vlastimil Babka Openpgp: preference=signencrypt Autocrypt: addr=vbabka@suse.cz; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1 MIME-Version: 1.0 In-Reply-To: <20181207061620.107881-2-drinkcat@chromium.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/7/18 7:16 AM, Nicolas Boichat wrote: > IOMMUs using ARMv7 short-descriptor format require page tables > to be allocated within the first 4GB of RAM, even on 64-bit systems. > On arm64, this is done by passing GFP_DMA32 flag to memory allocation > functions. > > For IOMMU L2 tables that only take 1KB, it would be a waste to allocate > a full page using get_free_pages, so we considered 3 approaches: > 1. This patch, adding support for GFP_DMA32 slab caches. > 2. genalloc, which requires pre-allocating the maximum number of L2 > page tables (4096, so 4MB of memory). > 3. page_frag, which is not very memory-efficient as it is unable > to reuse freed fragments until the whole page is freed. > > This change makes it possible to create a custom cache in DMA32 zone > using kmem_cache_create, then allocate memory using kmem_cache_alloc. > > We do not create a DMA32 kmalloc cache array, as there are currently > no users of kmalloc(..., GFP_DMA32). These calls will continue to > trigger a warning, as we keep GFP_DMA32 in GFP_SLAB_BUG_MASK. > > This implies that calls to kmem_cache_*alloc on a SLAB_CACHE_DMA32 > kmem_cache must _not_ use GFP_DMA32 (it is anyway redundant and > unnecessary). > > Signed-off-by: Nicolas Boichat Acked-by: Vlastimil Babka