On Fri 20-07-18 14:34:21, David Hildenbrand wrote: > The reserved bit once was used to hinder pages from getting swapped. While > this still works,
Does it? There is no single PageReserved check in the reclaim path. I have no idea when we stopped checking but it must be loooong ago. > the semantics are a little bit stronger nowadays: The > page should never be touched by anybody in the system except by the owner. > The original comment already gave a hint about that. > > So especially, these pages should also not be dumped by dumping tools. > Let's make that more clear by updating the comment. > > This will be useful especially in the future in virtual environments where > pages marked with the reserved bit might no longer be accessible. > > Cc: Andrew Morton <a...@linux-foundation.org> > Cc: Michal Hocko <mho...@suse.com> > Cc: Vlastimil Babka <vba...@suse.cz> > Cc: "Kirill A. Shutemov" <kirill.shute...@linux.intel.com> > Cc: Matthew Wilcox <mawil...@microsoft.com> > Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org> > Cc: David Hildenbrand <da...@redhat.com> > Cc: Huang Ying <ying.hu...@intel.com> > Cc: Pavel Tatashin <pasha.tatas...@oracle.com> > Cc: Miles Chen <miles.c...@mediatek.com> > Cc: Dave Young <dyo...@redhat.com> > Cc: Baoquan He <b...@redhat.com> > Cc: "Marc-André Lureau" <marcandre.lur...@redhat.com> > Cc: Petr Tesarik <ptesa...@suse.cz> > Signed-off-by: David Hildenbrand <da...@redhat.com> Anyway Acked-by: Michal Hocko <mho...@suse.com> for this change > --- > include/linux/page-flags.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 901943e4754b..ba81e11a868c 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -17,8 +17,8 @@ > /* > * Various page->flags bits: > * > - * PG_reserved is set for special pages, which can never be swapped out. Some > - * of them might not even exist... > + * PG_reserved is set for special pages, which should never be touched (read/ > + * write) by anybody except their owner. Some of them might not even exist. > * > * The PG_private bitflag is set on pagecache pages if they contain > filesystem > * specific data (which is normally at page->private). It can be used by > -- > 2.17.1 > -- Michal Hocko SUSE Labs
