On 01/13/2014 02:02 PM, Ingo Molnar wrote:
* Josef Bacik <jba...@fb.com> wrote:From: Josef Bacik <jba...@fusionio.com> Btrfs needs a simple way to know if it needs to let go of it's read lock on a rwsem. Introduce rwsem_is_contended to check to see if there are any waiters on this rwsem currently. This is just a hueristic, it is meant to be light and not 100% accurate and called by somebody already holding on to the rwsem in either read or write. Thanks, Signed-off-by: Josef Bacik <jba...@fusionio.com> --- include/linux/rwsem.h | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h index 0616ffe..03f3b05 100644 --- a/include/linux/rwsem.h +++ b/include/linux/rwsem.h @@ -75,6 +75,17 @@ do { \ } while (0)/*+ * This is the same regardless of which rwsem implementation that is being used. + * It is just a heuristic meant to be called by somebody alreadying holding the + * rwsem to see if somebody from an incompatible type is wanting access to the + * lock. + */ +static inline int rwsem_is_contended(struct rw_semaphore *sem) +{ + return !list_empty(&sem->wait_list); +} + +/* * lock for reading */ extern void down_read(struct rw_semaphore *sem);Looks good to me. To make it easier to merge 2/2 feel free to add this to the BTRFS tree, with my Acked-by: Acked-by: Ingo Molnar <mi...@kernel.org>
Great thanks Ingo, Josef -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
