linux-kernel - Re: [PATCH] mm/hugetlb: reduce arch dependent code about huge_pmd

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Date:	Fri, 24 Apr 2015 16:46:27 +0100
From:	Steve Capper <steve.capper@...aro.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Luck, Tony" <tony.luck@...el.com>,
	Zhang Zhen <zhenzhang.zhang@...wei.com>,
	Linux MM <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"catalin.marinas@....com" <catalin.marinas@....com>,
	"james.hogan@...tec.com" <james.hogan@...tec.com>,
	"ralf@...ux-mips.org" <ralf@...ux-mips.org>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
	"schwidefsky@...ibm.com" <schwidefsky@...ibm.com>,
	"cmetcalf@...hip.com" <cmetcalf@...hip.com>,
	David Rientjes <rientjes@...gle.com>,
	"James.Yang@...escale.com" <James.Yang@...escale.com>,
	"aneesh.kumar@...ux.vnet.ibm.com" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: [PATCH] mm/hugetlb: reduce arch dependent code about huge_pmd_unshare

Hi,

On 23 April 2015 at 23:41, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Thu, 23 Apr 2015 22:26:18 +0000 "Luck, Tony" <tony.luck@...el.com> wrote:
>
>> > Memory fails me.  Why do some architectures (arm, arm64, x86_64) want
>> > huge_pmd_[un]share() while other architectures (ia64, tile, mips,
>> > powerpc, metag, sh, s390) do not?
>>
>> Potentially laziness/ignorance-of-feature?  It looks like this feature started on x86_64 and then spread
>> to arm*.
>
> Yes.  In 3212b535f200c85b5a6 Steve Capper (ARM person) hoisted the code
> out of x86 into generic, then made arm use it.

I tested the pmd sharing code that x86 had and it worked well on ARM
too so I bundled it in when I generalised some of the huge page code.
I didn't know enough about the other architectures to enable it for
them, so played things safe by leaving it disabled for them.
Looking at this patch, I could have done that more cleanly though.

>
> We're not (I'm not) very good about letting arch people know about such
> things.  I wonder how to fix that; does linux-arch work?
>

linux-arch is working for me, maybe a good idea to CC in some arch
maintainers too.

Cheers,
-- 
Steve
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