On Thu, Oct 10, 2024 at 07:15:08AM -0700, Breno Leitao wrote:
> Whenever an I/O elevator is changed, the system attempts to load a
> module for the new elevator. This occurs regardless of whether the
> elevator is already loaded or built directly into the kernel. This
> behavior introduces unnecessary overhead and potential issues.
>
> This makes the operation slower, and more error-prone. For instance,
> making the problem fixed by [1] visible for users that doesn't even rely
> on modules being available through modules.
>
> Do not try to load the ioscheduler if it is already visible.
>
> This change brings two main benefits: it improves the performance of
> elevator changes, and it reduces the likelihood of errors occurring
> during this process.
>
> [1] Commit e3accac1a976 ("block: Fix elv_iosched_local_module handling of "none" scheduler")
> Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
> ---
> block/elevator.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/block/elevator.c b/block/elevator.c
> index 4122026b11f1..1904e217505a 100644
> --- a/block/elevator.c
> +++ b/block/elevator.c
> @@ -709,13 +709,16 @@ int elv_iosched_load_module(struct gendisk *disk, const char *buf,
> size_t count)
> {
> char elevator_name[ELV_NAME_MAX];
> + const char *name;
>
> if (!elv_support_iosched(disk->queue))
> return -EOPNOTSUPP;
>
> strscpy(elevator_name, buf, sizeof(elevator_name));
> + name = strstrip(elevator_name);
>
> - request_module("%s-iosched", strstrip(elevator_name));
> + if (!__elevator_find(name))
__elevator_find needs to be called with elv_list_lock.
