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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9ABDDC433EF for ; Fri, 7 Jan 2022 11:57:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238354AbiAGL47 (ORCPT ); Fri, 7 Jan 2022 06:56:59 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38176 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238445AbiAGL4p (ORCPT ); Fri, 7 Jan 2022 06:56:45 -0500 Received: from mail-pl1-x62c.google.com (mail-pl1-x62c.google.com [IPv6:2607:f8b0:4864:20::62c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4CFDAC034003; Fri, 7 Jan 2022 03:56:45 -0800 (PST) Received: by mail-pl1-x62c.google.com with SMTP id u16so4713690plg.9; Fri, 07 Jan 2022 03:56:45 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=JLgB+8SwNkq1hxQ6rMptEY0LB++ryMfLvvofb8EfBbs=; b=gPQ3FkicBPrX+aFjP0SyJpmjRm6CLsi6+aKZJVRRcQgGb4rsuHqN7+fXtKR1haiDFw h1OpOSFfZ738pdrAI5qr+b7c7uKT0KNseERh1pvJkwKXNfZZyaxo9vU/Ox7ZPTMnp9IR YFaqA75rAJ0+i9zMQdeaXeU7pHiwc807sRl7xRc0BLddaY6u6Fldv3zDd7Wp3jBIvnr1 D4XXpNTzRBawPzTgtkeX4qXUbgsV9PNyXhathIwnWHHHsmCrPDv205TRvhjmsCi2ZtPp wge7F5qu3IJwjSkQynmvaEnXPp1bUsVpm0cKkF7HKhtMf+sOgT4Sz7YeCuOvY8jK1EXk 7qCQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=JLgB+8SwNkq1hxQ6rMptEY0LB++ryMfLvvofb8EfBbs=; b=VpAo2sbTGcX9CQpS8GPPPxmGx5Q/ImXPudpgQkk6g3xzI6+U4819lR8EvvW4c1eqs6 wngA4j9M79vrAfnsD9usI/WpjOmHAhTlDyWsuZg/T6QZBpp0qLx4fSqQ3+xYGOtssGme RBi+P0HmNquNosRkoeYfIKZgfHrUgW+W4YrUVr9z+agE1LcgSbRXVFifEIYaVy/dEVXS P1kOf3bfF3MH/7YphrRO5UwlYbu5TQ+yyhCtoPpTBNvq9IA+Bz7Exb1zx70yePFGdv57 MioW4oTRyPf7bD5u+sLzVXwAq4PSqijN7oADU1pKuexh5wo5SwjUmij+XPCxCAciuuZK c7FQ== X-Gm-Message-State: AOAM531YGwfrRFp4adKFN+CfQZ9ZhBMXkW4+RaV+wZWOlfVwWnrunGUj AwGCy4RCw2dqLnE5ku3QchU= X-Google-Smtp-Source: ABdhPJwSKz9gRS4YXXsG0cGPlKpWY+DCW8zdfng9ZRZ47ARlJnxZvYrQS9W+LrU4kVWZyNJzWcY9uw== X-Received: by 2002:a17:902:8498:b0:149:f459:adfb with SMTP id c24-20020a170902849800b00149f459adfbmr6610921plo.85.1641556604847; Fri, 07 Jan 2022 03:56:44 -0800 (PST) Received: from odroid ([114.29.23.242]) by smtp.gmail.com with ESMTPSA id e11sm5301883pjh.14.2022.01.07.03.56.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Jan 2022 03:56:44 -0800 (PST) Date: Fri, 7 Jan 2022 11:56:38 +0000 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> To: Christoph Hellwig Cc: Vlastimil Babka , Baoquan He , linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, cl@linux.com, John.p.donnelly@oracle.com, kexec@lists.infradead.org, stable@vger.kernel.org, Pekka Enberg , David Rientjes , Joonsoo Kim Subject: Re: [PATCH v3 5/5] mm/slub: do not create dma-kmalloc if no managed pages in DMA zone Message-ID: <20220107115638.GB2769814@odroid> References: <20211213122712.23805-1-bhe@redhat.com> <20211213122712.23805-6-bhe@redhat.com> <20211213134319.GA997240@odroid> <20211214053253.GB2216@MiWiFi-R3L-srv> <20211215044818.GB1097530@odroid> <20211215070335.GA1165926@odroid> <20211215072710.GA3010@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211215072710.GA3010@lst.de> Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Wed, Dec 15, 2021 at 08:27:10AM +0100, Christoph Hellwig wrote: > On Wed, Dec 15, 2021 at 07:03:35AM +0000, Hyeonggon Yoo wrote: > > I'm not sure that allocating from ZONE_DMA32 instead of ZONE_DMA > > for kdump kernel is nice way to solve this problem. > > What is the problem with zones in kdump kernels? > > > Devices that requires ZONE_DMA memory is rare but we still support them. > > Indeed. > > > > 1) Do not call warn_alloc in page allocator if will always fail > > > to allocate ZONE_DMA pages. > > > > > > > > > 2) let's check all callers of kmalloc with GFP_DMA > > > if they really need GFP_DMA flag and replace those by DMA API or > > > just remove GFP_DMA from kmalloc() > > > > > > 3) Drop support for allocating DMA memory from slab allocator > > > (as Christoph Hellwig said) and convert them to use DMA32 > > > > (as Christoph Hellwig said) and convert them to use *DMA API* > > > > > and see what happens > > This is the right thing to do, but it will take a while. In fact > I dont think we really need the warning in step 1, a simple grep > already allows to go over them. I just looked at the uses of GFP_DMA > in drivers/scsi for example, and all but one look bogus. > > > > > > Yeah, I have the same guess too for get_capabilities(), not sure about other > > > > > callers. Or, as ChristophL and ChristophH said(Sorry, not sure if this is > > > > > the right way to call people when the first name is the same. Correct me if > > > > > it's wrong), any buffer requested from kmalloc can be used by device driver. > > > > > Means device enforces getting memory inside addressing limit for those > > > > > DMA transferring buffer which is usually large, Megabytes level with > > > > > vmalloc() or alloc_pages(), but doesn't care about this kind of small > > > > > piece buffer memory allocated with kmalloc()? Just a guess, please tell > > > > > a counter example if anyone happens to know, it could be easy. > > The way this works is that the dma_map* calls will bounce buffer memory > that does to fall into the addressing limitations. This is a performance > overhead, but allows drivers to address all memory in a system. If the > driver controls memory allocation it should use one of the dma_alloc_* > APIs that allocate addressable memory from the start. The allocator > will dip into ZONE_DMA and ZONE_DMA32 when needed. Hello Christoph, Baoquan and I started this cleanup. But we're a bit confused. I want to ask you something. - Did you mean dma_map_* can handle arbitrary buffer, (and dma_map_* will bounce buffer when necessary) Can we assume it on every architectures and buses? Reading at the DMA API documentation and code (dma_map_page_attrs(), dma_direct_map_page()), I'm not sure about that. In the documentation: (dma_map_single) Further, the DMA address of the memory must be within the dma_mask of the device (the dma_mask is a bit mask of the addressable region for the device, i.e., if the DMA address of the memory ANDed with the dma_mask is still equal to the DMA address, then the device can perform DMA to the memory). To ensure that the memory allocated by kmalloc is within the dma_mask, the driver may specify various platform-dependent flags to restrict the DMA address range of the allocation (e.g., on x86, GFP_DMA guarantees to be within the first 16MB of available DMA addresses, as required by ISA devices). - In what function does the DMA API do bounce buffering? Thanks a lot, Hyeonggon