io_uring/zcrx: netmem array as refiling format

Instead of peeking into page pool allocation cache directly or via
net_mp_netmem_place_in_cache(), pass a netmem array around. It's a
better intermediate format, e.g. you can have it on stack and reuse the
refilling code and decouples it from page pools a bit more.

It still points into the page pool directly, there will be no additional
copies. As the next step, we can change the callback prototype to take
the netmem array from page pool.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://patch.msgid.link/9d8549adb7ef6672daf2d8a52858ce5926279a82.1774261953.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: isilence

io_uring/zcrx.c

@@ -1011,19 +1011,21 @@ static inline bool io_parse_rqe(struct io_uring_zcrx_rqe *rqe,
 	return true;
 }
 
-static void io_zcrx_ring_refill(struct page_pool *pp,
-				struct io_zcrx_ifq *ifq)
+static unsigned io_zcrx_ring_refill(struct page_pool *pp,
+				    struct io_zcrx_ifq *ifq,
+				    netmem_ref *netmems, unsigned to_alloc)
 {
 	struct zcrx_rq *rq = &ifq->rq;
 	unsigned int mask = rq->nr_entries - 1;
 	unsigned int entries;
+	unsigned allocated = 0;
 
 	guard(spinlock_bh)(&rq->lock);
 
 	entries = zcrx_rq_entries(rq);
-	entries = min_t(unsigned, entries, PP_ALLOC_CACHE_REFILL);
+	entries = min_t(unsigned, entries, to_alloc);
 	if (unlikely(!entries))
-		return;
+		return 0;
 
 	do {
 		struct io_uring_zcrx_rqe *rqe = zcrx_next_rqe(rq, mask);
@@ -1045,48 +1047,56 @@ static void io_zcrx_ring_refill(struct page_pool *pp,
 		}
 
 		io_zcrx_sync_for_device(pp, niov);
-		net_mp_netmem_place_in_cache(pp, netmem);
+		netmems[allocated] = netmem;
+		allocated++;
 	} while (--entries);
 
 	smp_store_release(&rq->ring->head, rq->cached_head);
+	return allocated;
 }
 
-static void io_zcrx_refill_slow(struct page_pool *pp, struct io_zcrx_ifq *ifq)
+static unsigned io_zcrx_refill_slow(struct page_pool *pp, struct io_zcrx_ifq *ifq,
+				    netmem_ref *netmems, unsigned to_alloc)
 {
 	struct io_zcrx_area *area = ifq->area;
+	unsigned allocated = 0;
 
 	guard(spinlock_bh)(&area->freelist_lock);
 
-	while (pp->alloc.count < PP_ALLOC_CACHE_REFILL) {
+	for (allocated = 0; allocated < to_alloc; allocated++) {
 		struct net_iov *niov = zcrx_get_free_niov(area);
-		netmem_ref netmem;
 
 		if (!niov)
 			break;
 		net_mp_niov_set_page_pool(pp, niov);
 		io_zcrx_sync_for_device(pp, niov);
-		netmem = net_iov_to_netmem(niov);
-		net_mp_netmem_place_in_cache(pp, netmem);
+		netmems[allocated] = net_iov_to_netmem(niov);
 	}
+	return allocated;
 }
 
 static netmem_ref io_pp_zc_alloc_netmems(struct page_pool *pp, gfp_t gfp)
 {
 	struct io_zcrx_ifq *ifq = io_pp_to_ifq(pp);
+	netmem_ref *netmems = pp->alloc.cache;
+	unsigned to_alloc = PP_ALLOC_CACHE_REFILL;
+	unsigned allocated;
 
 	/* pp should already be ensuring that */
 	if (WARN_ON_ONCE(pp->alloc.count))
 		return 0;
 
-	io_zcrx_ring_refill(pp, ifq);
-	if (likely(pp->alloc.count))
+	allocated = io_zcrx_ring_refill(pp, ifq, netmems, to_alloc);
+	if (likely(allocated))
 		goto out_return;
 
-	io_zcrx_refill_slow(pp, ifq);
-	if (!pp->alloc.count)
+	allocated = io_zcrx_refill_slow(pp, ifq, netmems, to_alloc);
+	if (!allocated)
 		return 0;
 out_return:
-	return pp->alloc.cache[--pp->alloc.count];
+	allocated--;
+	pp->alloc.count += allocated;
+	return netmems[allocated];
 }
 
 static bool io_pp_zc_release_netmem(struct page_pool *pp, netmem_ref netmem)