Re: [PATCH v3 15/15] slab: Allocate frozen pages

[Matthew Wilcox <willy@infradead.org>]

On Wed, Nov 27, 2024 at 04:07:01PM +0100, David Hildenbrand wrote:
> I think we discussed in v1 or v2 that page isolation should be taught about that.
> 
> Likely we want something like:
> 
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index 7e04047977cfe..7db2f79b39f0d 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -101,6 +101,8 @@ static struct page *has_unmovable_pages(unsigned long start_pfn, unsigned long e
>                  * because their page->_refcount is zero at all time.
>                  */
>                 if (!page_ref_count(page)) {
> +                       if (PageSlab(page))
> +                               return page;
>                         if (PageBuddy(page))
>                                 pfn += (1 << buddy_order(page)) - 1;

Ah, for order 0 slabs!  I got caught up thinking that slabs would be
caught by the earlier PageTransCompound() check.  But that's also a
bit messy since we know that __folio_test_movable() can sometimes appear
true on slab pages.  So I'm tempted to hoist this way up to between the
check for ZONE_MOVABLE and PageHuge.