linux-kernel - Re: [Patch V2] xen: release lock occasionally during ballooning

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Date:	Mon, 20 Jul 2015 13:48:22 +0200
From:	Juergen Gross <jgross@...e.com>
To:	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	konrad.wilk@...cle.com, david.vrabel@...rix.com,
	boris.ostrovsky@...cle.com
Subject: Re: [Patch V2] xen: release lock occasionally during ballooning

Please ignore, forgot stg refresh...

Juergen

On 07/20/2015 01:46 PM, Juergen Gross wrote:
> When dom0 is being ballooned balloon_process() will hold the balloon
> mutex until it is finished. This will block e.g. creation of new
> domains as the device backends for the new domain need some
> autoballooned pages for the ring buffers.
>
> Avoid this by releasing the balloon mutex from time to time during
> ballooning. Adjust the comment above balloon_process() regarding
> multiple instances of balloon_process().
>
> Instead of open coding it, just use cond_resched().
>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
>   drivers/xen/balloon.c | 19 +++++++++++++++----
>   1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index fd93369..e6d9eee 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -481,9 +481,16 @@ static void balloon_process(struct work_struct *work)
>   {
>   	enum bp_state state = BP_DONE;
>   	long credit;
> +	static bool active;
>
>   	mutex_lock(&balloon_mutex);
>
> +	if (active) {
> +		mutex_unlock(&balloon_mutex);
> +		return;
> +	}
> +	active = true;
> +
>   	do {
>   		credit = current_credit();
>
> @@ -499,12 +506,16 @@ static void balloon_process(struct work_struct *work)
>
>   		state = update_schedule(state);
>
> -#ifndef CONFIG_PREEMPT
> -		if (need_resched())
> -			schedule();
> -#endif
> +		mutex_unlock(&balloon_mutex);
> +
> +		cond_resched();
> +
> +		mutex_lock(&balloon_mutex);
> +
>   	} while (credit && state == BP_DONE);
>
> +	active = false;
> +
>   	/* Schedule more work if there is some still to be done. */
>   	if (state == BP_EAGAIN)
>   		schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ);
>

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