Re: [PATCH v1 3/3] mm/ksm: move disabling KSM from s390/gmap code to KSM code

[David Hildenbrand]

On 19.04.23 13:39, Janosch Frank wrote:
> On 4/18/23 17:28, David Hildenbrand wrote:
> > Let's factor out actual disabling of KSM. The existing
> > "mm->def_flags &= ~VM_MERGEABLE;" was essentially a NOP and can be dropped,
> > because def_flags should never include VM_MERGEABLE. Note that we don't
> > currently prevent re-enabling KSM.
> >
> > This should now be faster in case KSM was never enabled, because we only
> > conditionally iterate all VMAs. Further, it certainly looks cleaner.
> >
> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> > ---
> >    arch/s390/mm/gmap.c | 20 +-------------------
> >    include/linux/ksm.h |  6 ++++++
> >    mm/ksm.c            | 11 +++++++++++
> >    3 files changed, 18 insertions(+), 19 deletions(-)
> >
> > diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> > index 0949811761e6..dfe905c7bd8e 100644
> > --- a/arch/s390/mm/gmap.c
> > +++ b/arch/s390/mm/gmap.c
> > @@ -2585,30 +2585,12 @@ EXPORT_SYMBOL_GPL(s390_enable_sie);
> >    
> >    int gmap_mark_unmergeable(void)
> >    {
> > -	struct mm_struct *mm = current->mm;
> > -	struct vm_area_struct *vma;
> > -	unsigned long vm_flags;
> > -	int ret;
> > -	VMA_ITERATOR(vmi, mm, 0);
> > -
> >    	/*
> >    	 * Make sure to disable KSM (if enabled for the whole process or
> >    	 * individual VMAs). Note that nothing currently hinders user space
> >    	 * from re-enabling it.
> >    	 */
>
> Is that still true?

Yes. We'd need another per-MM bit to stop it from getting re-enabled.

> My KSM knowledge is nearly zero but from what I can see the patch looks
> ok to me:
> Acked-by: Janosch Frank <frankja@xxxxxxxxxxxxx>


Thanks!

--
Thanks,

David / dhildenb