linux-kernel - Re: [PATCH v2] xen: Fix selfballooning and ensure it doesn't go too far

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Message-ID: <4E820316.6070101@citrix.com>
Date:	Tue, 27 Sep 2011 18:08:38 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
CC:	Konrad Wilk <konrad.wilk@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH v2] xen: Fix selfballooning and ensure it doesn't go too
 far

On 27/09/11 17:19, Dan Magenheimer wrote:
>> From: David Vrabel [mailto:david.vrabel@...rix.com]
>> Subject: Re: [PATCH v2] xen: Fix selfballooning and ensure it doesn't go too far
>>
>> On 27/09/11 16:03, Dan Magenheimer wrote:
>>> Note: This patch is also now in a git tree at:
>>>
>>> git://oss.oracle.com/git/djm/tmem.git#selfballoon-fix-v2
>>>
>>> The balloon driver's "current_pages" is very different from
>>> totalram_pages.  Self-ballooning needs to be driven by
>>> the latter.
> 
> Hi David --
> 
> Thanks for the feedback!
>  
>> I don't think this part of the change makes any difference. It looks like it
>> rearranges the maths without changing the end result (other than
>> slightly increasing the rate of change).
>> I think this (partial, untested) patch is equivalent:
> 
> Actually it does.

Really?

Both patched and unpatched the new target, S, is (eventually):

   S = V + F + C - T

where V is vm_committed_as, F is frontswap_curr_pages(), C is
balloon_stats.current_pages, and T = totalram_pages.

Perhaps the refactoring of the maths is a good idea (I don't think so)
but it shouldn't be part of this patch and it shouldn't be described as
a fix.

David
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