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

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Message-Id: <1242866163.27006.10125.camel@localhost.localdomain>
Date:	Wed, 20 May 2009 17:36:03 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	"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>,
	"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 Wed, 2009-05-20 at 17:08 -0700, Tejun Heo wrote:
> Heh... the problem is that unless I understand what you're trying to
> achieve (and vice-versa), our discussion is likely to be riddled with
> confusions, and currently either you're misunderstanding the whole
> thing or I'm being slow (not too unusual :-).  It would be nice to
> determine which way it is.

At the start of this, I was trying to see a way where we can use large
page mappings for percpu areas and at the same time, avoid the
complexity of cpa() that we are adding in this patchset. So, I was going
down the path of exploiting your bootmem allocation for the first percpu
chunk (as kernel identity mappings are already taken care by cpa()).

> The dynamic onlining will probably use 4k pages so, yeah, it won't
> have the alias issues but that's not the issue here, right?  You can
> already avoid aliasing that way by simply using 4k allocator from the
> get-go.

But now that I learnt about dynamic online allocation, can we avoid the
complexity brought by this patchset, by simply using 4k allocator from
get-go.

i.e., can we drop this remap pageattr handling patchset and simply use
4k mapping for now? And move to dynamic allocation at a later point.

This will simplify quite a bit of code.

thanks,
suresh

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