Commit 24139c07 authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
Browse files

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: default avatarDavid Hildenbrand <david@redhat.com>
Acked-by: default avatarStefan 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 70307b0e

include/linux/ksm.h

+1 −0
Original line number Diff line number Diff line
@@ -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);

kernel/sys.c

+3 −9
Original line number Diff line number Diff line
@@ -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:

mm/ksm.c

+59 −0
Original line number Diff line number Diff line
@@ -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)

{