Re: [PATCH 04/37] xen: introduce an arch helper for default dma zone status

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 23 Sep 2021, Wei Chen wrote:
> In current code, when Xen is running in a multiple nodes NUMA
> system, it will set dma_bitsize in end_boot_allocator to reserve
> some low address memory for DMA.
> 
> There are some x86 implications in current implementation. Becuase
                                    ^ the                    ^Because

> on x86, memory starts from 0. On a multiple nodes NUMA system, if
> a single node contains the majority or all of the DMA memory. x86
                                                              ^,

> prefer to give out memory from non-local allocations rather than
> exhausting the DMA memory ranges. Hence x86 use dma_bitsize to set
> aside some largely arbitrary amount memory for DMA memory ranges.
                                     ^ of memory

> The allocations from these memory ranges would happen only after
> exhausting all other nodes' memory.
> 
> But the implications are not shared across all architectures. For
> example, Arm doesn't have these implications. So in this patch, we
> introduce an arch_have_default_dmazone helper for arch to determine
> that it need to set dma_bitsize for reserve DMA allocations or not.
          ^ needs

> 
> Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> ---
>  xen/arch/x86/numa.c        | 5 +++++
>  xen/common/page_alloc.c    | 2 +-
>  xen/include/asm-arm/numa.h | 5 +++++
>  xen/include/asm-x86/numa.h | 1 +
>  4 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/arch/x86/numa.c b/xen/arch/x86/numa.c
> index ce79ee44ce..1fabbe8281 100644
> --- a/xen/arch/x86/numa.c
> +++ b/xen/arch/x86/numa.c
> @@ -371,6 +371,11 @@ unsigned int __init arch_get_dma_bitsize(void)
>                   + PAGE_SHIFT, 32);
>  }
>  
> +unsigned int arch_have_default_dmazone(void)

Can this function return bool?
Also, can it be a static inline?


> +{
> +    return ( num_online_nodes() > 1 ) ? 1 : 0;
> +}
> +
>  static void dump_numa(unsigned char key)
>  {
>      s_time_t now = NOW();
> diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
> index 5801358b4b..80916205e5 100644
> --- a/xen/common/page_alloc.c
> +++ b/xen/common/page_alloc.c
> @@ -1889,7 +1889,7 @@ void __init end_boot_allocator(void)
>      }
>      nr_bootmem_regions = 0;
>  
> -    if ( !dma_bitsize && (num_online_nodes() > 1) )
> +    if ( !dma_bitsize && arch_have_default_dmazone() )
>          dma_bitsize = arch_get_dma_bitsize();
>  
>      printk("Domain heap initialised");
> diff --git a/xen/include/asm-arm/numa.h b/xen/include/asm-arm/numa.h
> index 31a6de4e23..9d5739542d 100644
> --- a/xen/include/asm-arm/numa.h
> +++ b/xen/include/asm-arm/numa.h
> @@ -25,6 +25,11 @@ extern mfn_t first_valid_mfn;
>  #define node_start_pfn(nid) (mfn_x(first_valid_mfn))
>  #define __node_distance(a, b) (20)
>  
> +static inline unsigned int arch_have_default_dmazone(void)
> +{
> +    return 0;
> +}
> +
>  #endif /* __ARCH_ARM_NUMA_H */
>  /*
>   * Local variables:
> diff --git a/xen/include/asm-x86/numa.h b/xen/include/asm-x86/numa.h
> index 3cf26c2def..8060cbf3f4 100644
> --- a/xen/include/asm-x86/numa.h
> +++ b/xen/include/asm-x86/numa.h
> @@ -78,5 +78,6 @@ extern int valid_numa_range(u64 start, u64 end, nodeid_t 
> node);
>  void srat_parse_regions(u64 addr);
>  extern u8 __node_distance(nodeid_t a, nodeid_t b);
>  unsigned int arch_get_dma_bitsize(void);
> +unsigned int arch_have_default_dmazone(void);
>  
>  #endif
> -- 
> 2.25.1
>