On Mon, 11 Jan 2016, Aneesh Kumar K.V wrote:
> "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> writes:
> > Hugh Dickins <hughd@xxxxxxxxxx> writes:
> >
> >> 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.
> >
> >>
> >> 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.
Sure, please go ahead - thanks.
Hugh
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