Commit 4ccc6db0 authored by Uros Bizjak's avatar Uros Bizjak Committed by Jens Axboe
Browse files

io_uring: Use atomic_long_try_cmpxchg in __io_account_mem 



Use atomic_long_try_cmpxchg instead of
atomic_long_cmpxchg (*ptr, old, new) == old in __io_account_mem.
x86 CMPXCHG instruction returns success in ZF flag, so this
change saves a compare after cmpxchg (and related move
instruction in front of cmpxchg).

Also, atomic_long_try_cmpxchg implicitly assigns old *ptr value
to "old" when cmpxchg fails, enabling further code simplifications.

No functional change intended.

Signed-off-by: default avatarUros Bizjak <ubizjak@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 9bb66906

io_uring/rsrc.c

+3 −4
Original line number Diff line number Diff line
@@ -56,14 +56,13 @@ static inline int __io_account_mem(struct user_struct *user, 
	/* Don't allow more pages than we can safely lock */

	page_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;



	do {

	cur_pages = atomic_long_read(&user->locked_vm);

	do {

		new_pages = cur_pages + nr_pages;

		if (new_pages > page_limit)

			return -ENOMEM;

	} while (atomic_long_cmpxchg(&user->locked_vm, cur_pages,

					new_pages) != cur_pages);



	} while (!atomic_long_try_cmpxchg(&user->locked_vm,

					  &cur_pages, new_pages));

	return 0;

}