Re: [PATCH next] powerpc/mm: fix _PAGE_PTE breaking swapoff

"Aneesh Kumar K.V" [off-list ref] writes:

Hugh Dickins [off-list ref] writes:

quoted

Swapoff after swapping hangs on the G5.  That's because the _PAGE_PTE
bit, added by set_pte_at(), is not expected by swapoff: so swap ptes
cannot be recognized.

I'm not sure whether a swap pte should or should not have _PAGE_PTE set:
this patch assumes not, and fixes set_pte_at() to set _PAGE_PTE only on
present entries.

One of the reason we added _PAGE_PTE is to enable HUGETLB migration. So
we want migratio ptes to have _PAGE_PTE set.

quoted

But if that's wrong, a reasonable alternative would be to
#define __pte_to_swp_entry(pte)	((swp_entry_t) { pte_val(pte) & ~_PAGE_PTE })
#define __swp_entry_to_pte(x)	__pte((x).val | _PAGE_PTE)

You other email w.r.t soft dirty bits explained this. What I missed was
the fact that core kernel expect swp_entry_t to be of an arch neutral
format.  The confusing part was "arch_entry"

static inline pte_t swp_entry_to_pte(swp_entry_t entry)
{
	swp_entry_t arch_entry;
.....
}
	
IMHO we should use the alternative you suggested above. I can write a
patch with additional comments around that if you want me to do that.

-aneesh