From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E57801FECBA; Fri, 8 May 2026 11:46:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778240771; cv=none; b=buPX4INcYaK0rzcGE58zWwh3G0bl9Fv1/F4UNuoDTIxMEqScfpgwhAV03jdathR5XCNxvVlAlyL7KRTghrcFWb4/Nm0w9NaY7i1n5DoNDmqfSBTRCfvGBQwwEmez3kO8HeACBzAHBHH2yQABfh7RcfsDqVSrrrD0vrBag/BKXKg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778240771; c=relaxed/simple; bh=2kzRnBqgBU5KvKIDqJxGWoWinU1iXToqRq/hGbyW4rI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Fj//aegbSefYOMOww0v9ShcoyBDiCrJ8Ywrd5xKxQQJRzI9+YSOvFpXw+gb9ui56hmP7A+oILI9AvXUtwSldxTjpPkVYLVPguPCK+sbr4KEyxxwRV1K5a0R5Qq9E0Aj8MqEjoMeUIRkp2HbWA3EAED/HRZcrD8GVnpSlqoHlkgw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bqs1FXjS; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bqs1FXjS" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 13763C2BCB0; Fri, 8 May 2026 11:46:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778240770; bh=2kzRnBqgBU5KvKIDqJxGWoWinU1iXToqRq/hGbyW4rI=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=bqs1FXjS13wNgcrsExd9ewUN58pNMxoAP7eGdSlYnjyF9xKfP2iBHfxOe2KfZVREM 9gxfVARpua7JlcnWeFDB36Ex/f7obduxKx7a0GCETaRR9lUsUihaUKvaK18xEp9oXQ EY0CpVjwQJzDNGZVmxxjeVnj4xgCbadZtPEi+x6O7czh1R5FJzdEmTz2myEDvJV5r5 qBXv/Sp+zgF4dzaeaYRg1oDi+w5cSztHW6FsrRzRsCQnX51ZZY4sObGOlPDyPUTaaJ ileYHXScFqnzAik6050zNfYLeWzMHmZI+BsS7c9EbmjnQ3tlKrKYq/ykTeRAnIJPO3 cL2zQ6WDr2C6g== Message-ID: Date: Fri, 8 May 2026 13:46:03 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] dma-contiguous: setup default numa cma area if not configured explicitly To: Feng Tang Cc: Marek Szyprowski , Robin Murphy , Ying Huang , Andrew Morton , Lorenzo Stoakes , Liam.Howlett@oracle.com, Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, Christoph Hellwig , Catalin Marinas , Will Deacon , iommu@lists.linux.dev, linux-kernel@vger.kernel.org, Changrong Chen References: <20260428060550.7167-1-feng.tang@linux.alibaba.com> <6dd52f8b-7092-4d02-ba24-f8b55409b7b6@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/6/26 17:46, Feng Tang wrote: > On Fri, May 01, 2026 at 08:51:39PM +0200, David Hildenbrand (Arm) wrote: >> On 4/28/26 10:37, Feng Tang wrote: >>> Hi David, >> >> Hi! >> >> [...] >> >>> >>> Right for default kernel configs. >>> >>> In kernel/dma/Kconfig: >>> >>> config CMA_SIZE_MBYTES >>> int "Size in Mega Bytes" >>> depends on !CMA_SIZE_SEL_PERCENTAGE >>> default 0 if X86 >>> default 16 >>> >>> config CMA_SIZE_PERCENTAGE >>> int "Percentage of total memory" >>> depends on !CMA_SIZE_SEL_MBYTES >>> default 0 if X86 >>> default 10 >>> >>> >>> Yes. I thought about that, and didn't have good solution, and used this >>> given it's on a multi-numa-node machine, which may not be too bad >>> regarding memory usage. >> >> It sounds wrong given the existing config options. > > Yes, it is confusing. > >>> >>> Robin did concern about the memory usage for embedded/small devices in >>> v2 review, and we change to v3 to not affect them. >>> >>> >>> I agree :) >>> >>> >>> This sounds good to me, if no objection from others. Maybe default 64MB >>> or more. One good part is, all these setup is under protection of >>> CONFIG_DMA_NUMA_CMA. >> >> I cannot do the heavy thinking here because -EBUSY, but maybe you want a config >> option similar to CMA_SIZE_MBYTES/CMA_SIZE_PERCENTAGE that either controls that >> these sizes will be split over NUMA nodes, or another one, that sets the default >> for pernuma. > > Maybe a CMA_NUMA_SIZE_MBYTES? Maybe, I'm hoping some CMA DMA people have the capacity to provide input. > >> [...] >> >>> >>> My thought was 'struct cma' already have 'nid' member, and when CONFIG_NUMA=y, >>> it may be useful to save the 'nid' info instead of NUMA_NO_NODE for the default >>> cma area (cmdline like cma=XXG@YYG could make it on different node) >> >> Ah, yeah. It's a bit nasty that we have to handle the default area like that. >> >> Another sign that we probably shouldn't deal with the default area :) > > Yep, in v2 I didn't touch the default area, while Robin had a concern > that the v2 approach will bindly add an extra per-numa cma area for > the node which already has the default area, which will hurt those > small/embedded devices which has limited number of memory. Adding > the nid check is trying to keep the behavior of one node device > unchanged. > >>> >>> >>> Per my understanding, it won't. There is a cma_validate_zones() to prevent it >>> from crossing zones. >> >> It's a bit confusing, because it ignores other nids. > > I might have missed your point. Do you mean one cma are could have > multiple ranges? I don't know, it's confusing :) -- Cheers, David