linux-kernel - Re: [PATCH] replace various uses of num_physpages by totalram

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Message-Id: <4A8AE95C020000780001055F@vpn.id2.novell.com>
Date:	Tue, 18 Aug 2009 16:48:12 +0100
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	<linux-mm@...ck.org>, "Rusty Russell" <rusty@...tcorp.com.au>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] replace various uses of num_physpages by
	 totalram_pages

>>> Ingo Molnar <mingo@...e.hu> 18.08.09 17:38 >>>
>
>* Jan Beulich <JBeulich@...ell.com> wrote:
>
>> Sizing of memory allocations shouldn't depend on the number of 
>> physical pages found in a system, as that generally includes 
>> (perhaps a huge amount of) non-RAM pages. The amount of what 
>> actually is usable as storage should instead be used as a basis 
>> here.
>> 
>> Some of the calculations (i.e. those not intending to use high 
>> memory) should likely even use (totalram_pages - 
>> totalhigh_pages).
>> 
>> Signed-off-by: Jan Beulich <jbeulich@...ell.com>
>> Acked-by: Rusty Russell <rusty@...tcorp.com.au>
>> 
>> ---
>>  arch/x86/kernel/microcode_core.c  |    4 ++--
>
>Acked-by: Ingo Molnar <mingo@...e.hu>
>
>Just curious: how did you find this bug? Did you find this by 
>experiencing problems on a system with a lot of declared non-RAM 
>memory?

Actually, I noticed this on Xen (non-pv-ops) when booting a domain with
a sufficiently large initial balloon. Under that condition, booting would
frequently fail due to various table sizes being calculated way too large.

Jan

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