linux-kernel - vmalloc huge mappings

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Message-ID: <13ff700d-1dfc-4758-8621-8efa84481c73@arm.com>
Date: Thu, 7 Aug 2025 09:59:42 +0530
From: Dev Jain <dev.jain@....com>
To: npiggin@...il.com
Cc: linuxppc-dev@...ts.ozlabs.org, LKML <linux-kernel@...r.kernel.org>
Subject: vmalloc huge mappings

Hi Nicholas,

I was looking at all the previous discussions at [1] and [2], wherein 
vmalloc-huge was

switched on by default, and then had to be switched off on all arches 
after an year...

a) I am wondering whether ppc supports vmalloc-huge by default right now?

It doesn't look like it since the VM_ALLOW_HUGE_VMAP flag is still there.

b) From reading all the discussions, I could only figure two problems 
with vmalloc-huge - one

being the drivers operating on tail pages of a large page, thus needing 
us to split the compound page,

which has been solved. The other being partial permission change. Is 
there any other case I am missing,

or any other problems you speculate?

[1] https://lore.kernel.org/all/20220422060107.781512-2-npiggin@gmail.com/

[2] https://lore.kernel.org/all/20220415164413.2727220-1-song@kernel.org/