Re: [PATCH 1/2] xen: introduce a no lock version function of free_heap_pages

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 10/06/14 13:18, Bob Liu wrote:
> Function free_heap_pages() needs to get the heap_lock every time. This lock
> may become a problem when there are many CPUs trying to free pages in parallel.
>
> This patch introduces a no lock version function __free_heap_pages(), it can be
> used to free a batch of pages after grabbing the heap_lock.
>
> Signed-off-by: Bob Liu <bob.liu@oracle.com>
> ---
>  xen/common/page_alloc.c |   13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
> index 601319c..56826b4 100644
> --- a/xen/common/page_alloc.c
> +++ b/xen/common/page_alloc.c
> @@ -808,8 +808,8 @@ static int reserve_offlined_page(struct page_info *head)
>      return count;
>  }
>  
> -/* Free 2^@order set of pages. */
> -static void free_heap_pages(
> +/* No lock version, the caller must hold heap_lock */
> +static void __free_heap_pages(
>      struct page_info *pg, unsigned int order)
>  {
>      unsigned long mask, mfn = page_to_mfn(pg);
> @@ -819,8 +819,6 @@ static void free_heap_pages(
>      ASSERT(order <= MAX_ORDER);
>      ASSERT(node >= 0);

Probably best to insert an ASSERT(spin_is_locked(&heap_lock)) here.

~Andrew

>  
> -    spin_lock(&heap_lock);
> -
>      for ( i = 0; i < (1 << order); i++ )
>      {
>          /*
> @@ -894,7 +892,14 @@ static void free_heap_pages(
>  
>      if ( tainted )
>          reserve_offlined_page(pg);
> +}
>  
> +/* Free 2^@order set of pages. */
> +static void free_heap_pages(
> +    struct page_info *pg, unsigned int order)
> +{
> +    spin_lock(&heap_lock);
> +    __free_heap_pages(pg, order);
>      spin_unlock(&heap_lock);
>  }
>