Re: [PATCH v15 4/7] mm: Introduce Reported pages

[Nitesh Narayan Lal]

On 12/5/19 11:22 AM, Alexander Duyck wrote:
> From: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
>
> In order to pave the way for free page reporting in virtualized
> environments we will need a way to get pages out of the free lists and
> identify those pages after they have been returned. To accomplish this,
> this patch adds the concept of a Reported Buddy, which is essentially
> meant to just be the Uptodate flag used in conjunction with the Buddy
> page type.

[...]

> +enum {
> +	PAGE_REPORTING_IDLE = 0,
> +	PAGE_REPORTING_REQUESTED,
> +	PAGE_REPORTING_ACTIVE
> +};
> +
> +/* request page reporting */
> +static void
> +__page_reporting_request(struct page_reporting_dev_info *prdev)
> +{
> +	unsigned int state;
> +
> +	/* Check to see if we are in desired state */
> +	state = atomic_read(&prdev->state);
> +	if (state == PAGE_REPORTING_REQUESTED)
> +		return;
> +
> +	/*
> +	 *  If reporting is already active there is nothing we need to do.
> +	 *  Test against 0 as that represents PAGE_REPORTING_IDLE.
> +	 */
> +	state = atomic_xchg(&prdev->state, PAGE_REPORTING_REQUESTED);
> +	if (state != PAGE_REPORTING_IDLE)
> +		return;
> +
> +	/*
> +	 * Delay the start of work to allow a sizable queue to build. For
> +	 * now we are limiting this to running no more than once every
> +	 * couple of seconds.
> +	 */
> +	schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY);
> +}
> +

I think you recently switched to using an atomic variable for maintaining page
reporting status as I was doing in v12.
Which is good, as we will not have a disagreement on it now.

On a side note, apologies for not getting involved actively in the
discussions/reviews as I am on PTO.

-- 

Nitesh