| Message ID | 20180720123422.10127-2-david@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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 <akpm@linux-foundation.org> > Cc: Michal Hocko <mhocko@suse.com> > Cc: Vlastimil Babka <vbabka@suse.cz> > Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> > Cc: Matthew Wilcox <mawilcox@microsoft.com> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > Cc: David Hildenbrand <david@redhat.com> > Cc: Huang Ying <ying.huang@intel.com> > Cc: Pavel Tatashin <pasha.tatashin@oracle.com> > Cc: Miles Chen <miles.chen@mediatek.com> > Cc: Dave Young <dyoung@redhat.com> > Cc: Baoquan He <bhe@redhat.com> > Cc: "Marc-André Lureau" <marcandre.lureau@redhat.com> > Cc: Petr Tesarik <ptesarik@suse.cz> > Signed-off-by: David Hildenbrand <david@redhat.com> Anyway Acked-by: Michal Hocko <mhocko@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 >
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
The reserved bit once was used to hinder pages from getting swapped. While this still works, 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 <akpm@linux-foundation.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Matthew Wilcox <mawilcox@microsoft.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: David Hildenbrand <david@redhat.com> Cc: Huang Ying <ying.huang@intel.com> Cc: Pavel Tatashin <pasha.tatashin@oracle.com> Cc: Miles Chen <miles.chen@mediatek.com> Cc: Dave Young <dyoung@redhat.com> Cc: Baoquan He <bhe@redhat.com> Cc: "Marc-André Lureau" <marcandre.lureau@redhat.com> Cc: Petr Tesarik <ptesarik@suse.cz> Signed-off-by: David Hildenbrand <david@redhat.com> --- include/linux/page-flags.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)