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

["Vishal Moola (Oracle)" <vishal.moola@gmail.com>]

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.

> > two atomic operations (one on alloc, one on free) by allocating frozen
> > pages here.  This does not interfere with compaction as page tables are
> > non-movable allocations.
> > 
> > pagetable_alloc() and pagetable_free() need to move out of line to make
> > this work as alloc_frozen_page() and free_frozen_page() are not exported
> 
> Nit: s/page/pages/g
> 
> > outside the mm for now.  We'll want them out of line anyway soon.
> > 
> > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> 
> LGTM.
> Reviewed-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>

So I guess I retract this for now...