net: page_pool: scale alloc cache with PAGE_SIZE

The current page_pool alloc-cache size and refill values were chosen to
match the NAPI budget and to leave headroom for XDP_DROP recycling.
These fixed values do not scale well with large pages,
as they significantly increase a given page_pool's memory footprint.

Scale these values to better balance memory footprint across page sizes,
while keeping behavior on 4KB-page systems unchanged.

Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Nimrod Oren <noren@nvidia.com>
Link: https://patch.msgid.link/20260309081301.103152-1-noren@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/page_pool/types.h

@@ -44,6 +44,8 @@
  * use-case.  The NAPI budget is 64 packets.  After a NAPI poll the RX
  * ring is usually refilled and the max consumed elements will be 64,
  * thus a natural max size of objects needed in the cache.
+ * The refill watermark is set to 64 for 4KB pages,
+ * and scales to balance its size in bytes across page sizes.
  *
  * Keeping room for more objects, is due to XDP_DROP use-case.  As
  * XDP_DROP allows the opportunity to recycle objects directly into
@@ -51,8 +53,15 @@
  * cache is already full (or partly full) then the XDP_DROP recycles
  * would have to take a slower code path.
  */
-#define PP_ALLOC_CACHE_SIZE	128
+#if PAGE_SIZE >= SZ_64K
+#define PP_ALLOC_CACHE_REFILL	4
+#elif PAGE_SIZE >= SZ_16K
+#define PP_ALLOC_CACHE_REFILL	16
+#else
 #define PP_ALLOC_CACHE_REFILL	64
+#endif
+
+#define PP_ALLOC_CACHE_SIZE	(PP_ALLOC_CACHE_REFILL * 2)
 struct pp_alloc_cache {
 	u32 count;
 	netmem_ref cache[PP_ALLOC_CACHE_SIZE];