linux-kernel - Re: [PATCH v2 repost 6/7] mm: add the related functions to get free page info

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Message-ID: <5798E418.7080608@intel.com>
Date:	Wed, 27 Jul 2016 09:40:56 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Liang Li <liang.z.li@...el.com>, linux-kernel@...r.kernel.org
Cc:	virtualization@...ts.linux-foundation.org, linux-mm@...ck.org,
	virtio-dev@...ts.oasis-open.org, kvm@...r.kernel.org,
	qemu-devel@...gnu.org, dgilbert@...hat.com, quintela@...hat.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Mel Gorman <mgorman@...hsingularity.net>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Amit Shah <amit.shah@...hat.com>
Subject: Re: [PATCH v2 repost 6/7] mm: add the related functions to get free
 page info

On 07/26/2016 06:23 PM, Liang Li wrote:
> +	for_each_migratetype_order(order, t) {
> +		list_for_each(curr, &zone->free_area[order].free_list[t]) {
> +			pfn = page_to_pfn(list_entry(curr, struct page, lru));
> +			if (pfn >= start_pfn && pfn <= end_pfn) {
> +				page_num = 1UL << order;
> +				if (pfn + page_num > end_pfn)
> +					page_num = end_pfn - pfn;
> +				bitmap_set(bitmap, pfn - start_pfn, page_num);
> +			}
> +		}
> +	}

Nit:  The 'page_num' nomenclature really confused me here.  It is the
number of bits being set in the bitmap.  Seems like calling it nr_pages
or num_pages would be more appropriate.

Isn't this bitmap out of date by the time it's send up to the
hypervisor?  Is there something that makes the inaccuracy OK here?