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

David Hildenbrand david@redhat.com writes:

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.
  */
• clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
• for_each_vma(vmi, vma) {

• /* Copy vm_flags to avoid partial modifications in ksm_madvise */
  

• vm_flags = vma->vm_flags;
  

• ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
  

• 		  MADV_UNMERGEABLE, &vm_flags);
  

• if (ret)
  

• 	return ret;
  

• vm_flags_reset(vma, vm_flags);
  

• }
• mm->def_flags &= ~VM_MERGEABLE;

This clears the def_flags struct member, however, in ksm_disable() we clear the __flags struct member. Is this a problem?

• return 0;

• return ksm_disable(current->mm);

} EXPORT_SYMBOL_GPL(gmap_mark_unmergeable);

diff --git a/include/linux/ksm.h b/include/linux/ksm.h index 7108bc65dc2a..b3d8b7849e18 100644 --- a/include/linux/ksm.h +++ b/include/linux/ksm.h @@ -22,6 +22,7 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start, void ksm_add_vma(struct vm_area_struct *vma); int ksm_enable_merge_any(struct mm_struct *mm); int ksm_disable_merge_any(struct mm_struct *mm); +int ksm_disable(struct mm_struct *mm);

int __ksm_enter(struct mm_struct *mm); void __ksm_exit(struct mm_struct *mm); @@ -75,6 +76,11 @@ static inline void ksm_add_vma(struct vm_area_struct *vma) { }

+static inline int ksm_disable(struct mm_struct *mm) +{

• return 0;

+}

static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm) { return 0; diff --git a/mm/ksm.c b/mm/ksm.c index 813f7fbc1832..208311cbb019 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -2616,6 +2616,17 @@ int ksm_disable_merge_any(struct mm_struct *mm) return 0; }

+int ksm_disable(struct mm_struct *mm) +{

• mmap_assert_write_locked(mm);
• if (!test_bit(MMF_VM_MERGEABLE, &mm->flags))

• return 0;
  

• if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))

• return ksm_disable_merge_any(mm);
  

• return ksm_del_vmas(mm);

+}

int ksm_madvise(struct vm_area_struct *vma, unsigned long start, unsigned long end, int advice, unsigned long *vm_flags) {