linux-kernel - Re: [PATCH 09/13] mm/powerpc: Redefine pXd_huge() with pXd

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Message-ID: <2e632389-eb4e-42af-adee-36d5ba6c3d0f@csgroup.eu>
Date: Wed, 20 Mar 2024 17:40:39 +0000
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Peter Xu <peterx@...hat.com>, Aneesh Kumar K.V
	<aneesh.kumar@...ux.ibm.com>
CC: Jason Gunthorpe <jgg@...dia.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, Matthew Wilcox <willy@...radead.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>, Andrew
 Morton <akpm@...ux-foundation.org>, "x86@...nel.org" <x86@...nel.org>, Mike
 Rapoport <rppt@...nel.org>, Muchun Song <muchun.song@...ux.dev>,
	"sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>, Michael Ellerman
	<mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>, "Naveen N. Rao"
	<naveen.n.rao@...ux.ibm.com>
Subject: Re: [PATCH 09/13] mm/powerpc: Redefine pXd_huge() with pXd_leaf()



Le 20/03/2024 à 17:09, Peter Xu a écrit :
> On Wed, Mar 20, 2024 at 06:16:43AM +0000, Christophe Leroy wrote:
>> At the first place that was to get a close fit between hardware
>> pagetable topology and linux pagetable topology. But obviously we
>> already stepped back for 512k pages, so let's go one more step aside and
>> do similar with 8M pages.
>>
>> I'll give it a try and see how it goes.
> 
> So you're talking about 8M only for 8xx, am I right?

Yes I am.

> 
> There seem to be other PowerPC systems use hugepd.  Is it possible that we
> convert all hugepd into cont_pte form?

Indeed.

Seems like we have hugepd for book3s/64 and for nohash.

For book3s I don't know, may Aneesh can answer.

For nohash I think it should be possible because TLB misses are handled 
by software. Even the e6500 which has a hardware tablewalk falls back on 
software walk when it is a hugepage IIUC.

Christophe