linux-kernel - Re: [PATCH 1/2] mm: cma: NUMA node interface

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Date:   Thu, 2 Apr 2020 17:48:00 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Aslan Bakirov <aslan@...com>, akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kernel-team@...com, riel@...riel.com, guro@...com,
        mhocko@...nel.org, hannes@...xchg.org
Subject: Re: [PATCH 1/2] mm: cma: NUMA node interface

On 3/26/20 10:27 PM, Aslan Bakirov wrote:
> I've noticed that there is no interfaces exposed by CMA which would let me
> to declare contigous memory on particular NUMA node.
> 
> This patchset adds the ability to try to allocate contiguous memory on
> specific node.

I would say more explicitly that 'try' here means it will fallback to other
nodes if the specific one doesn't work. At least AFAICS that's what it does by
calling memblock_alloc_range_nid() with exact_nid=false.

> Implement a new method for declaring contigous memory on particular node
> and keep cma_declare_contiguous() as a wrapper.

Should there be also support for using this node spcification in the cma=X boot
param?

> Signed-off-by: Aslan Bakirov <aslan@...com>

...

> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -220,7 +220,7 @@ int __init cma_init_reserved_mem(phys_addr_t base, phys_addr_t size,
>  }
>  
>  /**
> - * cma_declare_contiguous() - reserve custom contiguous area
> + * cma_declare_contiguous_nid() - reserve custom contiguous area
>   * @base: Base address of the reserved area optional, use 0 for any
>   * @size: Size of the reserved area (in bytes),
>   * @limit: End address of the reserved memory (optional, 0 for any).
> @@ -229,6 +229,7 @@ int __init cma_init_reserved_mem(phys_addr_t base, phys_addr_t size,
>   * @fixed: hint about where to place the reserved area
>   * @name: The name of the area. See function cma_init_reserved_mem()
>   * @res_cma: Pointer to store the created cma region.
> + * @nid: nid of the free area to find, %NUMA_NO_NODE for any node

The bit about fallback should be also specified here.

>   *
>   * This function reserves memory from early allocator. It should be
>   * called by arch specific code once the early allocator (memblock or bootmem)
> @@ -238,10 +239,10 @@ int __init cma_init_reserved_mem(phys_addr_t base, phys_addr_t size,
>   * If @fixed is true, reserve contiguous area at exactly @base.  If false,
>   * reserve in range from @base to @limit.
>   */
> -int __init cma_declare_contiguous(phys_addr_t base,
> +int __init cma_declare_contiguous_nid(phys_addr_t base,
>  			phys_addr_t size, phys_addr_t limit,
>  			phys_addr_t alignment, unsigned int order_per_bit,
> -			bool fixed, const char *name, struct cma **res_cma)
> +			bool fixed, const char *name, struct cma **res_cma, int nid)
>  {
>  	phys_addr_t memblock_end = memblock_end_of_DRAM();
>  	phys_addr_t highmem_start;