On Tuesday, 2 March 2021 4:46:42 AM AEDT Jason Gunthorpe wrote:

I wish you could come up with a more descriptive word that special
here

What I understand is this is true when the swap_offset is a pfn?

Correct, and that points to a better name. Maybe is_pfn_swap_entry()? In which 
case adding a helper as Christoph suggested makes some more sense. Eg: 
pfn_swap_entry_to_page()

quoted

-static inline struct page *migration_entry_to_page(swp_entry_t entry)
-{
-	struct page *p = pfn_to_page(swp_offset(entry));
-	/*
-	 * Any use of migration entries may only occur while the
-	 * corresponding page is locked
-	 */
-	BUG_ON(!PageLocked(compound_head(p)));
-	return p;

And this constraint has been completely lost?

Yes, sorry I should have called that out. I didn't think loosing the check was 
a big deal, but I can add some checks to some of the call sites which would 
catch a page being incorrectly unlocked.

A comment in front of the is_special_entry explaining all the rule
would help alot

Will add one.

Transformation looks fine otherwise

Thanks.

 - Alistair
 

Jason