Re: [Xen-devel] [PATCH] xmalloc: return unused full pages on multi-page allocations

[Keir Fraser <keir@xxxxxxx>]

On 13/10/2011 08:27, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> Certain (boot time) allocations are relatively large (particularly when
> building with high NR_CPUS), but can also happen to be pretty far away
> from a power-of-two size. Utilize the page allocator's (other than
> Linux'es) capability of allowing to return space from higher-order
> allocations in smaller pieces to return the unused parts immediately.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Acked-by: Keir Fraser <keir@xxxxxxx>

> --- a/xen/common/xmalloc_tlsf.c
> +++ b/xen/common/xmalloc_tlsf.c
> @@ -527,13 +527,21 @@ static void xmalloc_pool_put(void *p)
>  static void *xmalloc_whole_pages(unsigned long size)
>  {
>      struct bhdr *b;
> -    unsigned int pageorder = get_order_from_bytes(size + BHDR_OVERHEAD);
> +    unsigned int i, pageorder = get_order_from_bytes(size + BHDR_OVERHEAD);
> +    char *p;
>  
>      b = alloc_xenheap_pages(pageorder, 0);
>      if ( b == NULL )
>          return NULL;
>  
> -    b->size = (1 << (pageorder + PAGE_SHIFT));
> +    b->size = PAGE_ALIGN(size + BHDR_OVERHEAD);
> +    for ( p = (char *)b + b->size, i = 0; i < pageorder; ++i )
> +        if ( (unsigned long)p & (PAGE_SIZE << i) )
> +        {
> +            free_xenheap_pages(p, i);
> +            p += PAGE_SIZE << i;
> +        }
> +
>      return (void *)b->ptr.buffer;
>  }
>  
> @@ -611,7 +619,20 @@ void xfree(void *p)
>      }
>  
>      if ( b->size >= PAGE_SIZE )
> -        free_xenheap_pages((void *)b, get_order_from_bytes(b->size));
> +    {
> +        unsigned int i, order = get_order_from_bytes(b->size);
> +
> +        BUG_ON((unsigned long)b & ((PAGE_SIZE << order) - 1));
> +        for ( i = 0; ; ++i )
> +        {
> +            if ( !(b->size & (PAGE_SIZE << i)) )
> +                continue;
> +            b->size -= PAGE_SIZE << i;
> +            free_xenheap_pages((void *)b + b->size, i);
> +            if ( i + 1 >= order )
> +                break;
> +        }
> +    }
>      else
>          xmem_pool_free(p, xenpool);
>  }
> 
> 
> 
> 
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