io_uring/alloc_cache: switch to array based caching

Currently lists are being used to manage this, but best practice is
usually to have these in an array instead as that it cheaper to manage.

Outside of that detail, games are also played with KASAN as the list
is inside the cached entry itself.

Finally, all users of this need a struct io_cache_entry embedded in
their struct, which is union'ized with something else in there that
isn't used across the free -> realloc cycle.

Get rid of all of that, and simply have it be an array. This will not
change the memory used, as we're just trading an 8-byte member entry
for the per-elem array size.

This reduces the overhead of the recycled allocations, and it reduces
the amount of code code needed to support recycling to about half of
what it currently is.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 5 insertions, 8 deletions

diff --git a/io_uring/net.c b/io_uring/net.c
index 3bef562b67de..d0abc5689066 100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -137,7 +137,7 @@ static void io_netmsg_recycle(struct io_kiocb *req, unsigned int issue_flags)
 
 	/* Let normal cleanup path reap it if we fail adding to the cache */
 	iov = hdr->free_iov;
-	if (io_alloc_cache_put(&req->ctx->netmsg_cache, &hdr->cache)) {
+	if (io_alloc_cache_put(&req->ctx->netmsg_cache, hdr)) {
 		if (iov)
 			kasan_mempool_poison_object(iov);
 		req->async_data = NULL;
@@ -148,12 +148,10 @@ static void io_netmsg_recycle(struct io_kiocb *req, unsigned int issue_flags)
 static struct io_async_msghdr *io_msg_alloc_async(struct io_kiocb *req)
 {
 	struct io_ring_ctx *ctx = req->ctx;
-	struct io_cache_entry *entry;
 	struct io_async_msghdr *hdr;
 
-	entry = io_alloc_cache_get(&ctx->netmsg_cache);
-	if (entry) {
-		hdr = container_of(entry, struct io_async_msghdr, cache);
+	hdr = io_alloc_cache_get(&ctx->netmsg_cache);
+	if (hdr) {
 		if (hdr->free_iov) {
 			kasan_mempool_unpoison_object(hdr->free_iov,
 				hdr->free_iov_nr * sizeof(struct iovec));
@@ -1490,11 +1488,10 @@ out:
 	return IOU_OK;
 }
 
-void io_netmsg_cache_free(struct io_cache_entry *entry)
+void io_netmsg_cache_free(const void *entry)
 {
-	struct io_async_msghdr *kmsg;
+	struct io_async_msghdr *kmsg = (struct io_async_msghdr *) entry;
 
-	kmsg = container_of(entry, struct io_async_msghdr, cache);
 	if (kmsg->free_iov) {
 		kasan_mempool_unpoison_object(kmsg->free_iov,
 				kmsg->free_iov_nr * sizeof(struct iovec));