Hi Jonathan,
Thanks!
On Tue, Aug 13, 2019 at 10:45:09AM -0700, Jonathan Lemon wrote:
> __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.
Acked-by: Ilias Apalodimas <ilias.apalodi...@linaro.org>
>
> Signed-off-by: Jonathan Lemon <jonathan.le...@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
>
