linux-kernel - [PATCH mel-git 3/3] net: page_pool: convert to use alloc_pages_bulk

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Date:   Wed, 24 Mar 2021 22:34:59 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Mel Gorman <mgorman@...hsingularity.net>, linux-mm@...ck.org
Cc:     Jesper Dangaard Brouer <brouer@...hat.com>, chuck.lever@...cle.com,
        Alexander Duyck <alexander.duyck@...il.com>,
        netdev@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH mel-git 3/3] net: page_pool: convert to use
 alloc_pages_bulk_array variant

Using the API variant alloc_pages_bulk_array from page_pool
was done in a separate patch to ease benchmarking the
variants separately.  Maintainers can squash patch if preferred.

Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
---
 include/net/page_pool.h |    2 +-
 net/core/page_pool.c    |   22 ++++++++++++++++------
 2 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index b5b195305346..6d517a37c18b 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h
@@ -65,7 +65,7 @@
 #define PP_ALLOC_CACHE_REFILL	64
 struct pp_alloc_cache {
 	u32 count;
-	void *cache[PP_ALLOC_CACHE_SIZE];
+	struct page *cache[PP_ALLOC_CACHE_SIZE];
 };
 
 struct page_pool_params {
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 3bf6e7f5fc89..9ec1aa9640ad 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -233,24 +233,34 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
 	const int bulk = PP_ALLOC_CACHE_REFILL;
 	unsigned int pp_flags = pool->p.flags;
 	unsigned int pp_order = pool->p.order;
-	struct page *page, *next;
-	LIST_HEAD(page_list);
+	struct page *page;
+	int i, nr_pages;
 
 	/* Don't support bulk alloc for high-order pages */
 	if (unlikely(pp_order))
 		return __page_pool_alloc_page_order(pool, gfp);
 
-	if (unlikely(!alloc_pages_bulk_list(gfp, bulk, &page_list)))
+	/* Unnecessary as alloc cache is empty, but guarantees zero count */
+	if (unlikely(pool->alloc.count > 0))
+		return pool->alloc.cache[--pool->alloc.count];
+
+	/* Mark empty alloc.cache slots "empty" for alloc_pages_bulk_array */
+	memset(&pool->alloc.cache, 0, sizeof(void *) * bulk);
+
+	nr_pages = alloc_pages_bulk_array(gfp, bulk, pool->alloc.cache);
+	if (unlikely(!nr_pages))
 		return NULL;
 
-	list_for_each_entry_safe(page, next, &page_list, lru) {
-		list_del(&page->lru);
+	/* Pages have been filled into alloc.cache array, but count is zero and
+	 * page element have not been (possibly) DMA mapped.
+	 */
+	for (i = 0; i < nr_pages; i++) {
+		page = pool->alloc.cache[i];
 		if ((pp_flags & PP_FLAG_DMA_MAP) &&
 		    unlikely(!page_pool_dma_map(pool, page))) {
 			put_page(page);
 			continue;
 		}
-		/* Alloc cache have room as it is empty on function call */
 		pool->alloc.cache[pool->alloc.count++] = page;
 		/* Track how many pages are held 'in-flight' */
 		pool->pages_state_hold_cnt++;