On Thu, Apr 04, 2019 at 09:21:52AM +0200, Peter Zijlstra wrote:
> On Wed, Apr 03, 2019 at 11:34:04AM -0600, Khalid Aziz wrote:
> > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> > index 2c471a2c43fa..d17d33f36a01 100644
> > --- a/include/linux/mm_types.h
> > +++ b/include/linux/mm_types.h
> > @@ -204,6 +204,14 @@ struct page {
> > #ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS
> > int _last_cpupid;
> > #endif
> > +
> > +#ifdef CONFIG_XPFO
> > + /* Counts the number of times this page has been kmapped. */
> > + atomic_t xpfo_mapcount;
> > +
> > + /* Serialize kmap/kunmap of this page */
> > + spinlock_t xpfo_lock;
>
> NAK, see ALLOC_SPLIT_PTLOCKS
>
> spinlock_t can be _huge_ (CONFIG_PROVE_LOCKING=y), also are you _really_
> sure you want spinlock_t and not raw_spinlock_t ? For
> CONFIG_PREEMPT_FULL spinlock_t turns into a rtmutex.
>
> > +#endif
>
> Growing the page-frame by 8 bytes (in the good case) is really sad,
> that's a _lot_ of memory.
Originally we had this in page_ext, it's not really clear to me why we
moved it out.
Julien?
Tycho
