Re: [PATCH 1/4] mm: Use frozen pages for page tables

[Will Deacon <will@kernel.org>]

On Thu, Nov 13, 2025 at 11:14:38AM -0800, Vishal Moola (Oracle) wrote:
> On Thu, Nov 13, 2025 at 10:24:27AM -0800, Vishal Moola (Oracle) wrote:
> > On Thu, Nov 13, 2025 at 02:04:43PM +0000, Matthew Wilcox (Oracle) wrote:
> > > Page tables do not use the reference count.  That means we can avoid
> 
> While looking into the second patch, I came across this one instance in
> sparc32. Commit 1996d47a0db ("sparc32: mm: Only call ctor()/dtor()
> functions for first and last user") decided to start using the refcount
> for something.
> 
> I'm not certain this code should even be using ptdescs, but theres a
> page_ptdesc() call in there for now :(.
> 
> As far as I can tell, this is only a thing for sparc32. Cc-ing Will as
> the author of those commits.

I'm afraid I've forgotten most of this as the only reason I found myself
hacking on sparc32 back in 2020 was because I was reworking READ_ONCE()
to operate only on scalar types and the srmmu code needed some surgery
to make that work.

However, from what I can tell/recall, pte_alloc_one() ends up calling
srmmu_get_nocache() which uses a custom allocator backed by a memblock
allocation from memblock_alloc_or_panic(). See srmmu_nocache_init().

Will