On 02/26, Christian Borntraeger wrote:
>
> On 26/02/14 15:50, Oleg Nesterov wrote:
> >
> > But perhaps qemu can be changed to avoid MADV_HUGEPAGE on s390 ?
> > Otherwise I'd suggest the change below.
> >
> > Oleg.
> >
> >
> > --- x/mm/huge_memory.c
> > +++ x/mm/huge_memory.c
> > @@ -1968,8 +1968,6 @@ out:
> > int hugepage_madvise(struct vm_area_struct *vma,
> > unsigned long *vm_flags, int advice)
> > {
> > - struct mm_struct *mm = vma->vm_mm;
> > -
> > switch (advice) {
> > case MADV_HUGEPAGE:
> > /*
> > @@ -1977,8 +1975,16 @@ int hugepage_madvise(struct vm_area_stru
> > */
> > if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP))
> > return -EINVAL;
> > - if (mm->def_flags & VM_NOHUGEPAGE)
> > +
> > +/*
> > + * MADV_HUGEPAGE after PRCTL_THP_DISABLE is broken on s390 because
> > + * qemu blindly does madvise(MADV_HUGEPAGE) after s390_enable_sie().
> > + */
> > +#ifdef CONFIG_S390
> > + if (vma->vm_mm->def_flags & VM_NOHUGEPAGE)
> > return -EINVAL;
> > +#endif
> > +
>
> Ifdefs are ugly but might be the only way of not breaking existing userspace.
Yes, agreed. but note that this code is already s390-specific, nobody
else puts VM_NOHUGEPAGE into ->def_flags (until this series of course).
> If we come up with a solution for THP in KVM host processes on s390, we can
> then remove that wart. We could even limit that hack to KVM only processes
> to retain Alex' prctl capability by checking mm_has_pgste
Yes, yes, I looked at mm->context.has_pgste too ;) But I wasn't sure
we can rely on it. Thanks.
> > +/*
> > + * MADV_HUGEPAGE after PRCTL_THP_DISABLE is broken on s390 because
> > + * qemu blindly does madvise(MADV_HUGEPAGE) after s390_enable_sie().
> > + */
> > +#ifdef CONFIG_S390
> > + if ((vma->vm_mm->def_flags & VM_NOHUGEPAGE) &&
> > mm_has_pgste(vma->vm_mm))
> > return -EINVAL;
Hmm... but why do we need to check VM_NOHUGEPAGE then? Can't the
change below work?
Oleg.
--- x/arch/s390/mm/pgtable.c
+++ x/arch/s390/mm/pgtable.c
@@ -1084,7 +1084,6 @@ static inline void thp_split_mm(struct m
vma->vm_flags &= ~VM_HUGEPAGE;
vma->vm_flags |= VM_NOHUGEPAGE;
}
- mm->def_flags |= VM_NOHUGEPAGE;
}
#else
static inline void thp_split_mm(struct mm_struct *mm)
--- x/mm/huge_memory.c
+++ x/mm/huge_memory.c
@@ -1968,8 +1968,6 @@ out:
int hugepage_madvise(struct vm_area_struct *vma,
unsigned long *vm_flags, int advice)
{
- struct mm_struct *mm = vma->vm_mm;
-
switch (advice) {
case MADV_HUGEPAGE:
/*
@@ -1977,8 +1975,12 @@ int hugepage_madvise(struct vm_area_stru
*/
if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP))
return -EINVAL;
- if (mm->def_flags & VM_NOHUGEPAGE)
+
+#ifdef CONFIG_S390
+ if (mm_has_pgste(vma->vm_mm))
return -EINVAL;
+#endif
+
*vm_flags &= ~VM_NOHUGEPAGE;
*vm_flags |= VM_HUGEPAGE;
/*
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
