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, 2 insertions, 5 deletions

diff --git a/io_uring/rw.h b/io_uring/rw.h
index cf51d0eb407a..3f432dc75441 100644
--- a/io_uring/rw.h
+++ b/io_uring/rw.h
@@ -3,10 +3,7 @@
 #include <linux/pagemap.h>
 
 struct io_async_rw {
-	union {
-		size_t			bytes_done;
-		struct io_cache_entry	cache;
-	};
+	size_t				bytes_done;
 	struct iov_iter			iter;
 	struct iov_iter_state		iter_state;
 	struct iovec			fast_iov;
@@ -28,4 +25,4 @@ void io_rw_fail(struct io_kiocb *req);
 void io_req_rw_complete(struct io_kiocb *req, struct io_tw_state *ts);
 int io_read_mshot_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
 int io_read_mshot(struct io_kiocb *req, unsigned int issue_flags);
-void io_rw_cache_free(struct io_cache_entry *entry);
+void io_rw_cache_free(const void *entry);