Re: [PATCH] blkcg: Optimize exit to user space

[Tejun Heo <tj@kernel.org>]

On Wed, Aug 13, 2025 at 04:59:57PM +0200, Thomas Gleixner wrote:
> blkcg uses TIF_NOTIFY_RESUME to handle throttling on exit to user
> space. TIF_NOTIFY_RESUME is a multiplexing TIF bit, which is utilized by
> other entities as well.
> 
> This results in a unconditional blkcg_maybe_throttle_current() call for
> every invocation of resume_user_mode_work(), which is a pointless exercise
> as most of the time there is no throttling work to do.
> 
> Optimize this by doing a quick check of the throttling condition before
> invoking it.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Josef Bacik <josef@toxicpanda.com>
> Cc: Jens Axboe <axboe@kernel.dk>
...
> -void blkcg_maybe_throttle_current(void)
> +void __blkcg_maybe_throttle_current(void)
>  {
>  	struct gendisk *disk = current->throttle_disk;
>  	struct blkcg *blkcg;

A nit: __blkcg_maybe_throttle_current() ends up doing another NULL check.
Maybe drop that? Other than that,

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun