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, 3 insertions, 9 deletions

diff --git a/io_uring/poll.c b/io_uring/poll.c
index 5d55bbf1de15..0a8e02944689 100644
--- a/io_uring/poll.c
+++ b/io_uring/poll.c
@@ -14,6 +14,7 @@
 #include <uapi/linux/io_uring.h>
 
 #include "io_uring.h"
+#include "alloc_cache.h"
 #include "refs.h"
 #include "napi.h"
 #include "opdef.h"
@@ -686,17 +687,15 @@ static struct async_poll *io_req_alloc_apoll(struct io_kiocb *req,
 					     unsigned issue_flags)
 {
 	struct io_ring_ctx *ctx = req->ctx;
-	struct io_cache_entry *entry;
 	struct async_poll *apoll;
 
 	if (req->flags & REQ_F_POLLED) {
 		apoll = req->apoll;
 		kfree(apoll->double_poll);
 	} else if (!(issue_flags & IO_URING_F_UNLOCKED)) {
-		entry = io_alloc_cache_get(&ctx->apoll_cache);
-		if (entry == NULL)
+		apoll = io_alloc_cache_get(&ctx->apoll_cache);
+		if (!apoll)
 			goto alloc_apoll;
-		apoll = container_of(entry, struct async_poll, cache);
 		apoll->poll.retries = APOLL_MAX_RETRY;
 	} else {
 alloc_apoll:
@@ -1055,8 +1054,3 @@ out:
 	io_req_set_res(req, ret, 0);
 	return IOU_OK;
 }
-
-void io_apoll_cache_free(struct io_cache_entry *entry)
-{
-	kfree(container_of(entry, struct async_poll, cache));
-}