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

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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>
This commit is contained in:
David Hildenbrand 2023-04-22 22:54:18 +02:00 committed by Andrew Morton
parent 70307b0e29
commit 24139c07f4
3 changed files with 63 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/ksm.h
View File

@ -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);

12
kernel/sys.c
View File

@ -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:

59
mm/ksm.c
View File

@ -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)
{