From 4ccc6db0900fe337212b61650663a5dcedb69f25 Mon Sep 17 00:00:00 2001 From: Uros Bizjak Date: Thu, 14 Jul 2022 18:33:01 +0200 Subject: 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: Uros Bizjak Cc: Jens Axboe Cc: Pavel Begunkov Signed-off-by: Jens Axboe --- io_uring/rsrc.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) (limited to 'io_uring/rsrc.c') diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c index 0250c13ae1cd..7f66b0e25674 100644 --- a/io_uring/rsrc.c +++ b/io_uring/rsrc.c @@ -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; + cur_pages = atomic_long_read(&user->locked_vm); do { - cur_pages = atomic_long_read(&user->locked_vm); 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; } -- cgit v1.2.3