mm/ksm: unmerge and clear VM_MERGEABLE when setting PR_SET_MEMORY_MERGE=0

Patch series "mm/ksm: improve PR_SET_MEMORY_MERGE=0 handling and cleanup
disabling KSM", v2.

(1) Make PR_SET_MEMORY_MERGE=0 unmerge pages like setting MADV_UNMERGEABLE
does, (2) add a selftest for it and (3) factor out disabling of KSM from
s390/gmap code.

This patch (of 3):

Let's unmerge any KSM pages when setting PR_SET_MEMORY_MERGE=0, and clear
the VM_MERGEABLE flag from all VMAs -- just like KSM would.  Of course,
only do that if we previously set PR_SET_MEMORY_MERGE=1.

Link: https://lkml.kernel.org/r/20230422205420.30372-1-david@redhat.com
Link: https://lkml.kernel.org/r/20230422205420.30372-2-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Stefan Roesch <shr@devkernel.io>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 7a9b76fb6c3f721686f9eee1e0f38a3c17ea74b6..429efa6ff4ae85b699857fb14b38f4ddb1494b6b 100644 (file)
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -21,6 +21,7 @@ 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_enter(struct mm_struct *mm);
 void __ksm_exit(struct mm_struct *mm);

diff --git a/kernel/sys.c b/kernel/sys.c
index 72cdb16e26366b17308b698abb7e91dcc12eb67d..339fee3eff6a2bb2f25d1663d91e17178302c03f 100644 (file)
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2695,16 +2695,10 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
                if (mmap_write_lock_killable(me->mm))
                        return -EINTR;
 
-               if (arg2) {
+               if (arg2)
                        error = ksm_enable_merge_any(me->mm);
-               } else {
-                       /*
-                        * TODO: we might want disable KSM on all VMAs and
-                        * trigger unsharing to completely disable KSM.
-                        */
-                       clear_bit(MMF_VM_MERGE_ANY, &me->mm->flags);
-                       error = 0;
-               }
+               else
+                       error = ksm_disable_merge_any(me->mm);
                mmap_write_unlock(me->mm);
                break;
        case PR_GET_MEMORY_MERGE:

diff --git a/mm/ksm.c b/mm/ksm.c
index 9e48258985d2f42ec3acd62787378e813eee3d4c..823bb3475a680ee7c6238e9950ee3fe8c65370f5 100644 (file)
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2520,6 +2520,22 @@ static void __ksm_add_vma(struct vm_area_struct *vma)
                vm_flags_set(vma, VM_MERGEABLE);
 }
 
+static int __ksm_del_vma(struct vm_area_struct *vma)
+{
+       int err;
+
+       if (!(vma->vm_flags & VM_MERGEABLE))
+               return 0;
+
+       if (vma->anon_vma) {
+               err = unmerge_ksm_pages(vma, vma->vm_start, vma->vm_end);
+               if (err)
+                       return err;
+       }
+
+       vm_flags_clear(vma, VM_MERGEABLE);
+       return 0;
+}
 /**
  * ksm_add_vma - Mark vma as mergeable if compatible
  *
@@ -2542,6 +2558,20 @@ static void ksm_add_vmas(struct mm_struct *mm)
                __ksm_add_vma(vma);
 }
 
+static int ksm_del_vmas(struct mm_struct *mm)
+{
+       struct vm_area_struct *vma;
+       int err;
+
+       VMA_ITERATOR(vmi, mm, 0);
+       for_each_vma(vmi, vma) {
+               err = __ksm_del_vma(vma);
+               if (err)
+                       return err;
+       }
+       return 0;
+}
+
 /**
  * ksm_enable_merge_any - Add mm to mm ksm list and enable merging on all
  *                        compatible VMA's
@@ -2569,6 +2599,35 @@ int ksm_enable_merge_any(struct mm_struct *mm)
        return 0;
 }
 
+/**
+ * ksm_disable_merge_any - Disable merging on all compatible VMA's of the mm,
+ *                        previously enabled via ksm_enable_merge_any().
+ *
+ * Disabling merging implies unmerging any merged pages, like setting
+ * MADV_UNMERGEABLE would. If unmerging fails, the whole operation fails and
+ * merging on all compatible VMA's remains enabled.
+ *
+ * @mm: Pointer to mm
+ *
+ * Returns 0 on success, otherwise error code
+ */
+int ksm_disable_merge_any(struct mm_struct *mm)
+{
+       int err;
+
+       if (!test_bit(MMF_VM_MERGE_ANY, &mm->flags))
+               return 0;
+
+       err = ksm_del_vmas(mm);
+       if (err) {
+               ksm_add_vmas(mm);
+               return err;
+       }
+
+       clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
+       return 0;
+}
+
 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
                unsigned long end, int advice, unsigned long *vm_flags)
 {