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 E45632F1FF4; Tue, 28 Apr 2026 07:52:23 +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=1777362744; cv=none; b=WuwGpDxzHddhB946vCevDM063FTfFA1WXkq23a8GJWWwxej09jaJIM+RB2frUboZqdamCQgkd4jsA0Z0SqEkJr/M2j1TyTxZE1fWXpTcCCZPfFzE8CQjXTjUKkjFWI6OV4YkBPVy6P1/e4YsvyK25e+xAOnNPniG1t5HCrJ+J9o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777362744; c=relaxed/simple; bh=KiGBp9SBRr0S2SXmmAPqSl+u4SEOgHA1uGT3SstawwI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=pqcx8wkVajfoC7QZdQIEj8vxvD6U6dMa4znLI/H37Pr3YObolGAztrFUz7S1c5k+HvTCElYBcZrYtjW3JwvZtsq0Qz8S0ugt2L7fra+O202oMAB17Z9Mt1hvYMGEWVKn+wKnGJOaa0+QOib4Wnb0w8lUiRpRWP4j5LLXZ1sQ1B8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GjLCFQjU; 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="GjLCFQjU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B08F6C2BCAF; Tue, 28 Apr 2026 07:52:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777362743; bh=KiGBp9SBRr0S2SXmmAPqSl+u4SEOgHA1uGT3SstawwI=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=GjLCFQjU5XtMIR8p2eUHF/UWAM3rz6xZtiteqH9mcF/Bbm0PvaCdhkYoFJLGQSAH6 NU+UqmQjnxZXYTuWhqjjm8pLO7oFBCYo+7rRTICVh4gAu67PGrqy90X1HVTMfio0E4 p35H3mRqvSxp47kRl96y94PYS6TM0FqgsBA89sR0EGpc7PfaGDp1yKJxz+SN67b8w9 GhHHdfFSgrTeOLdduvttmvYXLk4gsAiP9oUfNNhG9OwyzcAhwxyN2FGmmOMyfDjv7l WQU1ikAd8gcOb21b696ddPm2emWuXyL07t8Bxx9eFLZCAjBk2rh4RhpUAjz8Xklfjk Yrbw1tNNzGoVA== Message-ID: <6dd52f8b-7092-4d02-ba24-f8b55409b7b6@kernel.org> Date: Tue, 28 Apr 2026 09:52:15 +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 , Marek Szyprowski , Robin Murphy , Ying Huang , Andrew Morton Cc: 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> 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 4/28/26 08:05, Feng Tang wrote: > There was a report on a multi-numa-nodes ARM server that when IOMMU is > disabled, the dma_alloc_coherent() function always returns memory from > node 0 even for devices attaching to other nodes, while they can get > local dma memory when IOMMU is on with the same API. > > The reason is, when IOMMU is disabled, the dma_alloc_coherent() will > go the direct way and call dma_alloc_contiguous(). The system doesn't > have any explicit cma setting (like per-numa cma), and only has a > default 64MB cma reserved area (on node 0), where kernel will try > first to allocate memory from. > > Robin Murphy suggested to setup pernuma cma or disable cma, which did > solve the issue. That sounds like the obvious approach to me. > While there is still concern that for customers > which don't have much kernel knowledge, they could still suffer from > this silently as some architectures enable cma area by default (not > an issue for X86 though, which set CONFIG_CMA_SIZE_MBYTES to 0 by > default) for most Linux distributions. Okay, so on x86 it is not silent, because they don't even have a default CMA area? > > One thought is to follow the current cma reserving policy for platform > with 'CONFIG_DMA_NUMA_CMA=y', that if the numa cma (either the 'numa cma' > or 'cma pernuma' method) is not explicitly configured, set it up > according to size of default 'dma_contiguous_default_area', while > skipping the numa node where the 'dma_contiguous_default_area' lies > in, this way the default behavior of platform with one NUMA node is > kept unchanged. So, the kernel is configured to have a certain CONFIG_CMA_SIZE_MBYTES size, but you go ahead and multiply that by the number of nodes? Sounds wrong. The whole proposal here looks rather hacky. Wouldn't a default for e.g., pernuma_size_bytes make more sense, that users can then overwrite on the cmdline? > > To get the node info of cma area, add some helpr funciton and setup > in cma code. > > Reported-by: Changrong Chen > Suggested-by: Ying Huang > Suggested-by: Robin Murphy > Signed-off-by: Feng Tang > --- > Changelog: > > since v2: > * setup the numa cma are following default cma, while > skipping the node holds the default cma (Robin Murphy) > * add cma_get_node() help and related code > * add reporter info > > since v1: > * don't use the original way of adding alloc_pages_node() > before trying default cma node (Robin Murphy) > * setup default numa cma area if not configured (Ying Huang) > > v2: https://lore.kernel.org/lkml/20260423095243.14239-1-feng.tang@linux.alibaba.com/ > v1: https://lore.kernel.org/lkml/20260414090310.92055-1-feng.tang@linux.alibaba.com/ > > include/linux/cma.h | 1 + > kernel/dma/contiguous.c | 14 ++++++++++++-- > mm/cma.c | 11 ++++++++++- > 3 files changed, 23 insertions(+), 3 deletions(-) [...] > if (numa_cma_size[nid]) { > > cma = &dma_contiguous_numa_area[nid]; > @@ -255,8 +265,6 @@ void __init dma_contiguous_reserve(phys_addr_t limit) > phys_addr_t selected_limit = limit; > bool fixed = false; > > - dma_numa_cma_reserve(); > - > pr_debug("%s(limit %08lx)\n", __func__, (unsigned long)limit); > > if (size_cmdline != -1) { > @@ -312,6 +320,8 @@ void __init dma_contiguous_reserve(phys_addr_t limit) > if (ret) > pr_warn("Couldn't queue default CMA region for heap creation."); > } > + > + dma_numa_cma_reserve(); > } > > void __weak > diff --git a/mm/cma.c b/mm/cma.c > index c7ca567f4c5c..3bbfafeaf6c1 100644 > --- a/mm/cma.c > +++ b/mm/cma.c > @@ -54,6 +54,11 @@ const char *cma_get_name(const struct cma *cma) > } > EXPORT_SYMBOL_GPL(cma_get_name); > > +extern int cma_get_nid(const struct cma *cma) > +{ > + return cma->nid; > +} Why do you have to store the nid instead of just looking it up from the base_pfn in here? Also, what is the expectation when the ranges would span different NIDs? (is that possible?) -- Cheers, David