linux-kernel - Re: [PATCH] xen/balloon: Memory hotplug support for Xen balloon driver

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Message-ID: <1301327727.31700.8354.camel@nimitz>
Date:	Mon, 28 Mar 2011 08:55:27 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Daniel Kiper <dkiper@...-space.pl>
Cc:	ian.campbell@...rix.com, akpm@...ux-foundation.org,
	andi.kleen@...el.com, haicheng.li@...ux.intel.com,
	fengguang.wu@...el.com, jeremy@...p.org, konrad.wilk@...cle.com,
	dan.magenheimer@...cle.com, v.tolstov@...fip.ru, pasik@....fi,
	wdauchy@...il.com, rientjes@...gle.com,
	xen-devel@...ts.xensource.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] xen/balloon: Memory hotplug support for Xen balloon
 driver

On Mon, 2011-03-28 at 11:47 +0200, Daniel Kiper wrote:
> 
> +static enum bp_state reserve_additional_memory(long credit)
> +{
> +       int nid, rc;
> +       u64 start;
> +       unsigned long balloon_hotplug = credit;
> +
> +       start = PFN_PHYS(SECTION_ALIGN_UP(max_pfn));
> +       balloon_hotplug = (balloon_hotplug & PAGE_SECTION_MASK) + PAGES_PER_SECTION;
> +       nid = memory_add_physaddr_to_nid(start); 

Is the 'balloon_hotplug' calculation correct?  I _think_ you're trying
to round up to the SECTION_SIZE_PAGES.  But, if 'credit' was already
section-aligned I think you'll unnecessarily round up to the next
SECTION_SIZE_PAGES boundary.  Should it just be:

	balloon_hotplug = ALIGN(balloon_hotplug, PAGES_PER_SECTION);

You might also want to consider some nicer units for those suckers.
'start_paddr' is _much_ easier to grok than 'start', for instance.

-- Dave

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