linux-kernel - Re: [PATCH v5 02/18] mm: Define __pte_leaf

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Date: Tue, 11 Jun 2024 11:20:01 -0400
From: Peter Xu <peterx@...hat.com>
To: Oscar Salvador <osalvador@...e.de>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jason Gunthorpe <jgg@...dia.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v5 02/18] mm: Define __pte_leaf_size() to also take a PMD
 entry

On Tue, Jun 11, 2024 at 05:08:45PM +0200, Oscar Salvador wrote:
> The problem is that we do not have spare bits for 8xx to mark these ptes
> as cont-ptes or mark them pte as 8MB, so I do not see a clear path on how
> we could remove huge_ptep_get for 8xx.

Right, I remember I thought about this too when I initially looked at one
previous version of the series, I didn't come up yet with a good solution,
but I guess we probably need to get rid of hugepd first anyway.  We may
somehow still need to identify this is a 8M large leaf, and I guess this is
again the only special case where contpte can go over >1 pmds.

> 
> I am really curious though how we handle that for THP? Or THP on 8xx
> does not support that size?

I'll leave this to Christophe, but IIUC thp is only PMD_ORDER sized, so
shouldn't apply to the 8MB pages.

Thanks,

-- 
Peter Xu