linux-kernel - Re: [PATCHv1 6/8] xen/balloon: only hotplug additional memory if required

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Message-ID: <20150625211834.GO14050@olila.local.net-space.pl>
Date:	Thu, 25 Jun 2015 23:18:34 +0200
From:	Daniel Kiper <daniel.kiper@...cle.com>
To:	David Vrabel <david.vrabel@...rix.com>
Cc:	xen-devel@...ts.xenproject.org,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv1 6/8] xen/balloon: only hotplug additional memory if
 required

On Thu, Jun 25, 2015 at 06:11:01PM +0100, David Vrabel wrote:
> Now that we track the total number of pages (included hotplugged
> regions), it is easy to determine if more memory needs to be
> hotplugged.
>
> Signed-off-by: David Vrabel <david.vrabel@...rix.com>
> ---
>  drivers/xen/balloon.c |   16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index 960ac79..dd41da8 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -241,12 +241,22 @@ static void release_memory_resource(struct resource *resource)
>   * bit set). Real size of added memory is established at page onlining stage.
>   */
>
> -static enum bp_state reserve_additional_memory(long credit)
> +static enum bp_state reserve_additional_memory(void)
>  {
> +	long credit;
>  	struct resource *resource;
>  	int nid, rc;
>  	unsigned long balloon_hotplug;
>
> +	credit = balloon_stats.target_pages - balloon_stats.total_pages;
> +
> +	/*
> +	 * Already hotplugged enough pages?  Wait for them to be
> +	 * onlined.
> +	 */

Comment is wrong or at least misleading. Both values does not depend on onlining.

> +	if (credit <= 0)
> +		return BP_EAGAIN;

Not BP_EAGAIN for sure. It should be BP_DONE but then balloon_process() will go
into loop until memory is onlined at least up to balloon_stats.target_pages.
BP_ECANCELED does work but it is misleading because it is not an error. So, maybe
we should introduce BP_STOP (or something like that) which works like BP_ECANCELED
and is not BP_ECANCELED.

Daniel
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