On Thu, Jul 11, 2024 at 07:24:33PM +0200, David Hildenbrand wrote: > On 11.07.24 19:17, Jason A. Donenfeld wrote: > > On Thu, Jul 11, 2024 at 07:09:36PM +0200, Jason A. Donenfeld wrote: > >> So, hmm... The swapbacked thing really seemed so simple... I wonder if > >> there's a way of recovering that. > > > > Not wanting to introduce a new bitflag, I went looking and noticed this: > > > > /* > > * Private page markings that may be used by the filesystem that owns the page > > * for its own purposes. > > * - PG_private and PG_private_2 cause release_folio() and co to be invoked > > */ > > PAGEFLAG(Private, private, PF_ANY) > > PAGEFLAG(Private2, private_2, PF_ANY) TESTSCFLAG(Private2, private_2, PF_ANY) > > PAGEFLAG(OwnerPriv1, owner_priv_1, PF_ANY) > > TESTCLEARFLAG(OwnerPriv1, owner_priv_1, PF_ANY) > > > > The below +4/-1 diff is pretty hacky and might be illegal in the state > > of California, but I think it does work. The idea is that if that bit is > > normally only used for filesystems, then in the anonymous case, it's > > free to be used for this. > > > > Any opinions about this, or a suggestion on how to do that in a less > > ugly way? > > > > Jason > > > > > > diff --git a/mm/rmap.c b/mm/rmap.c > > index 1f9b5a9cb121..090554277e4a 100644 > > --- a/mm/rmap.c > > +++ b/mm/rmap.c > > @@ -1403,6 +1403,8 @@ void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma, > > */ > > if (!(vma->vm_flags & VM_DROPPABLE)) > > __folio_set_swapbacked(folio); > > + else > > + folio_set_owner_priv_1(folio); > > > PG_owner_priv_1 maps to PG_swapcache? :) Oh, drat, it looks like this overloading is nothing new then.
