From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCH v2 repost 6/7] mm: add the related functions to get free
 page info
Date: Wed, 27 Jul 2016 09:40:56 -0700
Message-ID: <5798E418.7080608@intel.com>
References: <1469582616-5729-1-git-send-email-liang.z.li@intel.com>
 <1469582616-5729-7-git-send-email-liang.z.li@intel.com>
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Cc: virtualization@lists.linux-foundation.org, linux-mm@kvack.org,
 virtio-dev@lists.oasis-open.org, kvm@vger.kernel.org, qemu-devel@nongnu.org,
 dgilbert@redhat.com, quintela@redhat.com,
 Andrew Morton <akpm@linux-foundation.org>, Vlastimil Babka <vbabka@suse.cz>,
 Mel Gorman <mgorman@techsingularity.net>, "Michael S. Tsirkin"
 <mst@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>,
 Cornelia Huck <cornelia.huck@de.ibm.com>, Amit Shah <amit.shah@redhat.com>
To: Liang Li <liang.z.li@intel.com>, linux-kernel@vger.kernel.org
Return-path: <owner-linux-mm@kvack.org>
In-Reply-To: <1469582616-5729-7-git-send-email-liang.z.li@intel.com>
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List-Id: kvm.vger.kernel.org

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Isn't this bitmap out of date by the time it's send up to the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?

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