linux-kernel - Re: [PATCH v2 2/2] arm64: mm: reserve per-numa CMA after numa

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Date:   Thu, 25 Jun 2020 12:15:50 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Barry Song <song.bao.hua@...ilicon.com>, hch@....de,
        m.szyprowski@...sung.com, will@...nel.org,
        ganapatrao.kulkarni@...ium.com, catalin.marinas@....com
Cc:     iommu@...ts.linux-foundation.org, linuxarm@...wei.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Steve Capper <steve.capper@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.ibm.com>
Subject: Re: [PATCH v2 2/2] arm64: mm: reserve per-numa CMA after numa_init

On 2020-06-25 08:43, Barry Song wrote:
> Right now, smmu is using dma_alloc_coherent() to get memory to save queues
> and tables. Typically, on ARM64 server, there is a default CMA located at
> node0, which could be far away from node2, node3 etc.
> with this patch, smmu will get memory from local numa node to save command
> queues and page tables. that means dma_unmap latency will be shrunk much.
> Meanwhile, when iommu.passthrough is on, device drivers which call dma_
> alloc_coherent() will also get local memory and avoid the travel between
> numa nodes.
> 
> Cc: Christoph Hellwig <hch@....de>
> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Robin Murphy <robin.murphy@....com>
> Cc: Ganapatrao Kulkarni <ganapatrao.kulkarni@...ium.com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
> Cc: Steve Capper <steve.capper@....com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Mike Rapoport <rppt@...ux.ibm.com>
> Signed-off-by: Barry Song <song.bao.hua@...ilicon.com>
> ---
>   arch/arm64/mm/init.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 1e93cfc7c47a..07d4d1fe7983 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -420,6 +420,8 @@ void __init bootmem_init(void)
>   
>   	arm64_numa_init();
>   
> +	dma_pernuma_cma_reserve();
> +

It might be worth putting this after the hugetlb_cma_reserve() call for 
clarity, since the comment below applies equally to this call too.

Robin.

>   	/*
>   	 * must be done after arm64_numa_init() which calls numa_init() to
>   	 * initialize node_online_map that gets used in hugetlb_cma_reserve()
>