Re: [Xen-devel] [PATCH v3 19/20] xen/privcmd: Add support for Linux 64KB page granularity

From: David Vrabel <david.vrabel@citrix.com>
To: Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
	Julien Grall <julien.grall@citrix.com>
Cc: <ian.campbell@citrix.com>, <linux-kernel@vger.kernel.org>,
	David Vrabel <david.vrabel@citrix.com>,
	<xen-devel@lists.xenproject.org>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [Xen-devel] [PATCH v3 19/20] xen/privcmd: Add support for Linux 64KB page granularity
Date: Mon, 10 Aug 2015 13:14:32 +0100	[thread overview]
Message-ID: <55C895A8.9020004@citrix.com> (raw)
In-Reply-To: <alpine.DEB.2.02.1508101230260.11337@kaball.uk.xensource.com>

On 10/08/15 13:03, Stefano Stabellini wrote:
> On Fri, 7 Aug 2015, Julien Grall wrote:
>> -	rc = HYPERVISOR_memory_op(XENMEM_add_to_physmap_range, &xatp);
>> -	return rc < 0 ? rc : err;
>> +	for (i = 0; i < nr_gfn; i++) {
>> +		if ((i % XEN_PFN_PER_PAGE) == 0) {
>> +			page = pages[i / XEN_PFN_PER_PAGE];
> 
> If this function is going to be called very frequently you might want to
> consider using a shift instead.
> 
>     page = pages[i >> 4];
> 
> With an appropriate macro of course.

This change isn't necessary.  Compilers already turn divides into
suitable shifts.

David