linux-kernel - Re: [GIT PATCH] x86,percpu: fix pageattr handling with remap allocator

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Message-Id: <1242436626.27006.8623.camel@localhost.localdomain>
Date:	Fri, 15 May 2009 18:17:06 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	"JBeulich@...ell.com" <JBeulich@...ell.com>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"linux-kernel-owner@...r.kernel.org" 
	<linux-kernel-owner@...r.kernel.org>,
	"hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PATCH] x86,percpu: fix pageattr handling with remap
 allocator

On Thu, 2009-05-14 at 05:49 -0700, Tejun Heo wrote:
> Hello,
> 
> Upon ack, please pull from the following git tree.
> 
>  git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git x86-percpu-pageattr
> 
> This patchset fixes subtile bug in pageattr handling when remap percpu
> first chunk allocator is in use and implements percpu_alloc kernel
> parameter so that allocator can be selected from boot prompt.
> 
> This problem was spotted by Jan Beulich.
> 
> The remap allocator allocates a PMD page per cpu, returns whatever is
> unnecessary to the page allocator and remaps the PMD page into vmalloc
> area to construct the first percpu chunk.  This is to take advantage
> of large page mapping.  

Tejun, Can you please educate me why we need to map this first percpu
chunk (which is pre-allocated during boot and is physically contiguous)
into vmalloc area? Perhaps even for the other dynamically allocated
secondary chunks? (as far as I can see, all the chunk allocations seems
to be physically contiguous and later mapped into vmalloc area)..

That should simplify these things quite a bit(atleast for first percpu
chunk). I am missing something obvious I guess.

thanks,
suresh

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