Re: [PATCH for-7.5 5/5] memcg: simplify high limit handling after a charge

[Michal Hocko <mhocko@suse.com>]

On Sat 10-10-26 14:09:57, Shakeel Butt wrote:
[...]
> -	/* Interrupts, kernel threads, and remote chargers stop here. */
> -	if (use_worker)
> +	/*
> +	 * Use a worker for interrupts, kernel threads, and tasks whose mm
> +	 * does not match the charged hierarchy.
> +	 */
> +	if (use_high_work) {
> +		if (!iter)
> +			return;
> +		if (allow_spinning)
> +			schedule_work(&iter->high_work);
> +		else
> +			irq_work_queue(&iter->high_irq_work);
>  		return;
> +	}
> +
> +	if (iter) {

Would it be much simpler to bail out on iter==NULL (i.e. nothing over
high limit) right after the loop?

> +		/*
> +		 * Count the full batch so reclaim work and delay penalties scale
> +		 * with the pages charged by this task.
> +		 */
> +		current->memcg_nr_pages_over_high += nr_pages;
> +		set_notify_resume(current);
> +	}
>  
>  	/*
> -	 * Reclaim is set up above to be called from the userland
> -	 * return path. But also attempt synchronous reclaim to avoid
> -	 * excessive overrun while the task is still inside the
> -	 * kernel. If this is successful, the return path will see it
> -	 * when it rechecks the overage and simply bail out.
> +	 * Earlier charges may have left high overage pending even if this charge
> +	 * found no new overage. Handle it now if this charge can block, to limit
> +	 * overrun while the task remains in the kernel.
>  	 */
>  	if (current->memcg_nr_pages_over_high > MEMCG_CHARGE_BATCH &&
>  	    !(current->flags & PF_MEMALLOC) &&
> -- 
> 2.53.0-Meta

-- 
Michal Hocko
SUSE Labs