netdev.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Jonathan Lemon <jonathan.lemon@gmail.com>
To: <netdev@vger.kernel.org>, <davem@davemloft.net>
Cc: <brouer@redhat.com>, <ilias.apalodimas@linaro.org>,
	<saeedm@mellanox.com>, <ttoukan.linux@gmail.com>,
	<kernel-team@fb.com>
Subject: [PATCH net-next] page_pool: fix logic in __page_pool_get_cached
Date: Tue, 13 Aug 2019 10:45:09 -0700	[thread overview]
Message-ID: <20190813174509.494723-1-jonathan.lemon@gmail.com> (raw)

__page_pool_get_cached() will return NULL when the ring is
empty, even if there are pages present in the lookaside cache.

It is also possible to refill the cache, and then return a
NULL page.

Restructure the logic so eliminate both cases.

Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
---
 net/core/page_pool.c | 39 ++++++++++++++++-----------------------
 1 file changed, 16 insertions(+), 23 deletions(-)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 68510eb869ea..de09a74a39a4 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -82,12 +82,9 @@ EXPORT_SYMBOL(page_pool_create);
 static struct page *__page_pool_get_cached(struct page_pool *pool)
 {
 	struct ptr_ring *r = &pool->ring;
+	bool refill = false;
 	struct page *page;
 
-	/* Quicker fallback, avoid locks when ring is empty */
-	if (__ptr_ring_empty(r))
-		return NULL;
-
 	/* Test for safe-context, caller should provide this guarantee */
 	if (likely(in_serving_softirq())) {
 		if (likely(pool->alloc.count)) {
@@ -95,27 +92,23 @@ static struct page *__page_pool_get_cached(struct page_pool *pool)
 			page = pool->alloc.cache[--pool->alloc.count];
 			return page;
 		}
-		/* Slower-path: Alloc array empty, time to refill
-		 *
-		 * Open-coded bulk ptr_ring consumer.
-		 *
-		 * Discussion: the ring consumer lock is not really
-		 * needed due to the softirq/NAPI protection, but
-		 * later need the ability to reclaim pages on the
-		 * ring. Thus, keeping the locks.
-		 */
-		spin_lock(&r->consumer_lock);
-		while ((page = __ptr_ring_consume(r))) {
-			if (pool->alloc.count == PP_ALLOC_CACHE_REFILL)
-				break;
-			pool->alloc.cache[pool->alloc.count++] = page;
-		}
-		spin_unlock(&r->consumer_lock);
-		return page;
+		refill = true;
 	}
 
-	/* Slow-path: Get page from locked ring queue */
-	page = ptr_ring_consume(&pool->ring);
+	/* Quicker fallback, avoid locks when ring is empty */
+	if (__ptr_ring_empty(r))
+		return NULL;
+
+	/* Slow-path: Get page from locked ring queue,
+	 * refill alloc array if requested.
+	 */
+	spin_lock(&r->consumer_lock);
+	page = __ptr_ring_consume(r);
+	if (refill)
+		pool->alloc.count = __ptr_ring_consume_batched(r,
+							pool->alloc.cache,
+							PP_ALLOC_CACHE_REFILL);
+	spin_unlock(&r->consumer_lock);
 	return page;
 }
 
-- 
2.17.1


             reply	other threads:[~2019-08-13 17:45 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-13 17:45 Jonathan Lemon [this message]
2019-08-14 12:29 ` [PATCH net-next] page_pool: fix logic in __page_pool_get_cached Jesper Dangaard Brouer
2019-08-14 12:49 ` Ilias Apalodimas
2019-08-15 19:28 ` David Miller

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190813174509.494723-1-jonathan.lemon@gmail.com \
    --to=jonathan.lemon@gmail.com \
    --cc=brouer@redhat.com \
    --cc=davem@davemloft.net \
    --cc=ilias.apalodimas@linaro.org \
    --cc=kernel-team@fb.com \
    --cc=netdev@vger.kernel.org \
    --cc=saeedm@mellanox.com \
    --cc=ttoukan.linux@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).