[PATCH 17/17] io_uring: defer flushing cached reqs

[Pavel Begunkov <asml.silence@xxxxxxxxx>]

Awhile there are requests in the allocation cache -- use them, only if
those ended go for the stashed memory in comp.free_list. As list
manipulation are generally heavy and are not good for caches, flush them
all or as much as can in one go.

Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
---
 fs/io_uring.c | 29 +++++++++++++++++++----------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 64d3f3e2e93d..17194e0d62ff 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1953,25 +1953,34 @@ static inline void io_req_complete(struct io_kiocb *req, long res)
 	__io_req_complete(req, 0, res, 0);
 }
 
+static void io_flush_cached_reqs(struct io_submit_state *state)
+{
+	do {
+		struct io_kiocb *req = list_first_entry(&state->comp.free_list,
+						struct io_kiocb, compl.list);
+
+		list_del(&req->compl.list);
+		state->reqs[state->free_reqs++] = req;
+		if (state->free_reqs == ARRAY_SIZE(state->reqs))
+			break;
+	} while (!list_empty(&state->comp.free_list));
+}
+
 static struct io_kiocb *io_alloc_req(struct io_ring_ctx *ctx)
 {
 	struct io_submit_state *state = &ctx->submit_state;
 
 	BUILD_BUG_ON(IO_REQ_ALLOC_BATCH > ARRAY_SIZE(state->reqs));
 
-	if (!list_empty(&state->comp.free_list)) {
-		struct io_kiocb *req;
-
-		req = list_first_entry(&state->comp.free_list, struct io_kiocb,
-					compl.list);
-		list_del(&req->compl.list);
-		return req;
-	}
-
 	if (!state->free_reqs) {
 		gfp_t gfp = GFP_KERNEL | __GFP_NOWARN;
 		int ret;
 
+		if (!list_empty(&state->comp.free_list)) {
+			io_flush_cached_reqs(state);
+			goto out;
+		}
+
 		ret = kmem_cache_alloc_bulk(req_cachep, gfp, IO_REQ_ALLOC_BATCH,
 					    state->reqs);
 
@@ -1987,7 +1996,7 @@ static struct io_kiocb *io_alloc_req(struct io_ring_ctx *ctx)
 		}
 		state->free_reqs = ret;
 	}
-
+out:
 	state->free_reqs--;
 	return state->reqs[state->free_reqs];
 }
-- 
2.24.0