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

David Hildenbrand
2023-04-19T11:41:15Z

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@redhat.com>
>> ---
>> 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@linux.ibm.net>

Thanks!

--
Thanks,

David / dhildenb