These are effectively the sum of free memory in all zones of each node.
It's an optimization to avoid doing that operation frequently in
following patches that introduce exact-node claims.

Signed-off-by: Alejandro Vallejo <alejandro.vallejo@cloud.com>
---
 xen/common/page_alloc.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 49c3258169db..733b0300a767 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -485,6 +485,9 @@ static unsigned long node_need_scrub[MAX_NUMNODES];
 static unsigned long *avail[MAX_NUMNODES];
 static long total_avail_pages;
 
+/* Per-node counts of free pages */
+static unsigned long pernode_avail_pages[MAX_NUMNODES];
+
 static DEFINE_SPINLOCK(heap_lock);
 static long outstanding_claims; /* total outstanding claims by all domains */
 
@@ -1033,6 +1036,7 @@ static struct page_info *alloc_heap_pages(
 
     ASSERT(avail[node][zone] >= request);
     avail[node][zone] -= request;
+    pernode_avail_pages[node] -= request;
     total_avail_pages -= request;
     ASSERT(total_avail_pages >= 0);
 
@@ -1191,6 +1195,8 @@ static int reserve_offlined_page(struct page_info *head)
             continue;
 
         avail[node][zone]--;
+        ASSERT(pernode_avail_pages[node] > 0);
+        pernode_avail_pages[node]--;
         total_avail_pages--;
         ASSERT(total_avail_pages >= 0);
 
@@ -1515,6 +1521,7 @@ static void free_heap_pages(
     }
 
     avail[node][zone] += 1 << order;
+    pernode_avail_pages[node] += 1 << order;
     total_avail_pages += 1 << order;
     if ( need_scrub )
     {
-- 
2.48.1

On 14.03.2025 18:24, Alejandro Vallejo wrote:
> --- a/xen/common/page_alloc.c
> +++ b/xen/common/page_alloc.c
> @@ -485,6 +485,9 @@ static unsigned long node_need_scrub[MAX_NUMNODES];
>  static unsigned long *avail[MAX_NUMNODES];
>  static long total_avail_pages;
>  
> +/* Per-node counts of free pages */
> +static unsigned long pernode_avail_pages[MAX_NUMNODES];

Performance-wise I find concerning any addition of yet another array like
this one, which - unlike e.g. avail[] - is randomly written from all nodes.
I think we either need to introduce per_node() paralleling per_cpu(), or
(less desirable, but perhaps easier to carry out) data structures need to
be introduced to make sure one particular cache line would only ever be
written from a single node. As it's visible from patch context:
node_need_scrub[] could/should move there, too, for example.

Jan

On Fri, Mar 14, 2025 at 05:24:54PM +0000, Alejandro Vallejo wrote:
> These are effectively the sum of free memory in all zones of each node.
> It's an optimization to avoid doing that operation frequently in
> following patches that introduce exact-node claims.
> 
> Signed-off-by: Alejandro Vallejo <alejandro.vallejo@cloud.com>
> ---
>  xen/common/page_alloc.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
> index 49c3258169db..733b0300a767 100644
> --- a/xen/common/page_alloc.c
> +++ b/xen/common/page_alloc.c
> @@ -485,6 +485,9 @@ static unsigned long node_need_scrub[MAX_NUMNODES];
>  static unsigned long *avail[MAX_NUMNODES];
>  static long total_avail_pages;
>  
> +/* Per-node counts of free pages */
> +static unsigned long pernode_avail_pages[MAX_NUMNODES];
> +
>  static DEFINE_SPINLOCK(heap_lock);
>  static long outstanding_claims; /* total outstanding claims by all domains */
>  
> @@ -1033,6 +1036,7 @@ static struct page_info *alloc_heap_pages(
>  
>      ASSERT(avail[node][zone] >= request);
>      avail[node][zone] -= request;
> +    pernode_avail_pages[node] -= request;

Since it's done for the per-zone tracking, you might as well add:

ASSERT(pernode_avail_pages[node] >= request);

here?

Thanks, Roger.