[net-next v6 PATCH 2/2] page_pool: help compiler remove code in case CONFIG_NUMA=n

Jesper Dangaard Brouer
2019-12-27T17:13:34Z

When kernel is compiled without NUMA support, then page_pool NUMA
config setting (pool->p.nid) doesn't make any practical sense. The
compiler cannot see that it can remove the code paths.

This patch avoids reading pool->p.nid setting in case of !CONFIG_NUMA,
in allocation and numa check code, which helps compiler to see the
optimisation potential. It leaves update code intact to keep API the
same.

$ ./scripts/bloat-o-meter net/core/page_pool.o-numa-enabled \
net/core/page_pool.o-numa-disabled
add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-113 (-113)
Function old new delta
page_pool_create 401 398 -3
__page_pool_alloc_pages_slow 439 426 -13
page_pool_refill_alloc_cache 425 328 -97
Total: Before=3611, After=3498, chg -3.13%

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
net/core/page_pool.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 748f0d36f4be..28fe694f9ab2 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -113,7 +113,12 @@ static struct page *page_pool_refill_alloc_cache(struct page_pool *pool,
/* Softirq guarantee CPU and thus NUMA node is stable. This,
* assumes CPU refilling driver RX-ring will also run RX-NAPI.
*/
+#ifdef CONFIG_NUMA
pref_nid = (pool->p.nid == NUMA_NO_NODE) ? numa_mem_id() : pool->p.nid;
+#else
+ /* Ignore pool->p.nid setting if !CONFIG_NUMA, helps compiler */
+ pref_nid = numa_mem_id(); /* will be zero like page_to_nid() */
+#endif

/* Slower-path: Get pages from locked ring queue */
spin_lock(&r->consumer_lock);
@@ -200,7 +205,11 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
*/

/* Cache was empty, do real allocation */
+#ifdef CONFIG_NUMA
page = alloc_pages_node(pool->p.nid, gfp, pool->p.order);
+#else
+ page = alloc_pages(gfp, pool->p.order);
+#endif
if (!page)
return NULL;