[...]
Thanks for giving mu sugegstions a churn. I think we can further
improve/simplify some things. I added some comments, but might have more
regarding MMF_VM_MERGE_ANY / MMF_VM_MERGEABLE.
[I'll try reowkring your patch after I send this mail to play with some
simplifications]
arch/s390/mm/gmap.c | 1 +
include/linux/ksm.h | 23 +++++--
include/linux/sched/coredump.h | 1 +
include/uapi/linux/prctl.h | 2 +
kernel/fork.c | 1 +
kernel/sys.c | 23 +++++++
mm/ksm.c | 111 ++++++++++++++++++++++++++-------
mm/mmap.c | 7 +++
8 files changed, 142 insertions(+), 27 deletions(-)
diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index 5a716bdcba05..9d85e5589474 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -2591,6 +2591,7 @@ int gmap_mark_unmergeable(void)
int ret;
VMA_ITERATOR(vmi, mm, 0);
+ clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
Okay, that should keep the existing mechanism working. (but users can
still mess it up)
Might be worth a comment
/*
* 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.
*/
for_each_vma(vmi, vma) {
/* Copy vm_flags to avoid partial modifications in ksm_madvise */
vm_flags = vma->vm_flags;
diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 7e232ba59b86..f24f9faf1561 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -18,20 +18,29 @@
#ifdef CONFIG_KSM
int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
unsigned long end, int advice, unsigned long *vm_flags);
-int __ksm_enter(struct mm_struct *mm);
-void __ksm_exit(struct mm_struct *mm);
+
+int ksm_add_mm(struct mm_struct *mm);
+void ksm_add_vma(struct vm_area_struct *vma);
+void ksm_add_vmas(struct mm_struct *mm);
+
+int __ksm_enter(struct mm_struct *mm, int flag);
+void __ksm_exit(struct mm_struct *mm, int flag);
static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
{
+ if (test_bit(MMF_VM_MERGE_ANY, &oldmm->flags))
+ return ksm_add_mm(mm);
ksm_fork() runs before copying any VMAs. Copying the bit should be
sufficient.
Would it be possible to rework to something like:
if (test_bit(MMF_VM_MERGE_ANY, &oldmm->flags))
set_bit(MMF_VM_MERGE_ANY, &mm->flags)
if (test_bit(MMF_VM_MERGEABLE, &oldmm->flags))
return __ksm_enter(mm);
work? IOW, not exporting ksm_add_mm() and not passing a flag to
__ksm_enter() -- it would simply set MMF_VM_MERGEABLE ?
I rememebr proposing that enabling MMF_VM_MERGE_ANY would simply enable
MMF_VM_MERGEABLE.
if (test_bit(MMF_VM_MERGEABLE, &oldmm->flags))
- return __ksm_enter(mm);
+ return __ksm_enter(mm, MMF_VM_MERGEABLE);
return 0;
}
static inline void ksm_exit(struct mm_struct *mm)
{
- if (test_bit(MMF_VM_MERGEABLE, &mm->flags))
- __ksm_exit(mm);
+ if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))
+ __ksm_exit(mm, MMF_VM_MERGE_ANY);
+ else if (test_bit(MMF_VM_MERGEABLE, &mm->flags))
+ __ksm_exit(mm, MMF_VM_MERGEABLE);
Can we do
if (test_bit(MMF_VM_MERGEABLE, &mm->flags))
__ksm_exit(mm);
And simply let __ksm_exit() clear both bits?
}
/*
@@ -53,6 +62,10 @@ void folio_migrate_ksm(struct folio *newfolio, struct folio *folio);
#else /* !CONFIG_KSM */
[...]
#endif /* _LINUX_SCHED_COREDUMP_H */
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 1312a137f7fb..759b3f53e53f 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -290,4 +290,6 @@ struct prctl_mm_map {
#define PR_SET_VMA 0x53564d41
# define PR_SET_VMA_ANON_NAME 0
+#define PR_SET_MEMORY_MERGE 67
+#define PR_GET_MEMORY_MERGE 68
#endif /* _LINUX_PRCTL_H */
diff --git a/kernel/fork.c b/kernel/fork.c
index f68954d05e89..1520697cf6c7 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -686,6 +686,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
if (vma_iter_bulk_store(&vmi, tmp))
goto fail_nomem_vmi_store;
+ ksm_add_vma(tmp);
Is this really required? The relevant VMAs should have VM_MERGEABLE set.
mm->map_count++;
if (!(tmp->vm_flags & VM_WIPEONFORK))
retval = copy_page_range(tmp, mpnt);
diff --git a/kernel/sys.c b/kernel/sys.c
index 495cd87d9bf4..9bba163d2d04 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -15,6 +15,7 @@
#include <linux/highuid.h>
#include <linux/fs.h>
#include <linux/kmod.h>
+#include <linux/ksm.h>
#include <linux/perf_event.h>
#include <linux/resource.h>
#include <linux/kernel.h>
@@ -2661,6 +2662,28 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
case PR_SET_VMA:
error = prctl_set_vma(arg2, arg3, arg4, arg5);
break;
+#ifdef CONFIG_KSM
+ case PR_SET_MEMORY_MERGE:
+ if (mmap_write_lock_killable(me->mm))
+ return -EINTR;
+
+ if (arg2) {
+ int err = ksm_add_mm(me->mm);
+
+ if (!err)
+ ksm_add_vmas(me->mm);
+ } else {
+ clear_bit(MMF_VM_MERGE_ANY, &me->mm->flags);
Okay, so disabling doesn't actually unshare anything.
+ }
+ mmap_write_unlock(me->mm);
+ break;
+ case PR_GET_MEMORY_MERGE:
+ if (arg2 || arg3 || arg4 || arg5)
+ return -EINVAL;
+
+ error = !!test_bit(MMF_VM_MERGE_ANY, &me->mm->flags);
+ break;
+#endif
default:
error = -EINVAL;
break;
diff --git a/mm/ksm.c b/mm/ksm.c
index d7bd28199f6c..ab95ae0f9def 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -534,10 +534,33 @@ static int break_ksm(struct vm_area_struct *vma, unsigned long addr,
return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
}
+static bool vma_ksm_compatible(struct vm_area_struct *vma)
+{
+ if (vma->vm_flags & (VM_SHARED | VM_MAYSHARE | VM_PFNMAP |
+ VM_IO | VM_DONTEXPAND | VM_HUGETLB |
+ VM_MIXEDMAP))
+ return false; /* just ignore the advice */
+
+ if (vma_is_dax(vma))
+ return false;
+
+#ifdef VM_SAO
+ if (vma->vm_flags & VM_SAO)
+ return false;
+#endif
+#ifdef VM_SPARC_ADI
+ if (vma->vm_flags & VM_SPARC_ADI)
+ return false;
+#endif
+
+ return true;
+}
+
static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
unsigned long addr)
{
struct vm_area_struct *vma;
+
unrelated change
if (ksm_test_exit(mm))
return NULL;
vma = vma_lookup(mm, addr);
@@ -1065,6 +1088,7 @@ static int unmerge_and_remove_all_rmap_items(void)
mm_slot_free(mm_slot_cache, mm_slot);
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
+ clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
mmdrop(mm);
} else
spin_unlock(&ksm_mmlist_lock);
@@ -2495,6 +2519,7 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
mm_slot_free(mm_slot_cache, mm_slot);
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
+ clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
mmap_read_unlock(mm);
mmdrop(mm);
} else {
@@ -2571,6 +2596,63 @@ static int ksm_scan_thread(void *nothing)
return 0;
}
+static void __ksm_add_vma(struct vm_area_struct *vma)
+{
+ unsigned long vm_flags = vma->vm_flags;
+
+ if (vm_flags & VM_MERGEABLE)
+ return;
+
+ if (vma_ksm_compatible(vma)) {
+ vm_flags |= VM_MERGEABLE;
+ vm_flags_reset(vma, vm_flags);
+ }
+}
+
+/**
+ * ksm_add_vma - Mark vma as mergeable
"if compatible"
+ *
+ * @vma: Pointer to vma
+ */
+void ksm_add_vma(struct vm_area_struct *vma)
+{
+ struct mm_struct *mm = vma->vm_mm;
+
+ if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))
+ __ksm_add_vma(vma);
+}
+
+/**
+ * ksm_add_vmas - Mark all vma's of a process as mergeable
+ *
+ * @mm: Pointer to mm
+ */
+void ksm_add_vmas(struct mm_struct *mm)
I'd suggest calling this
+{
+ struct vm_area_struct *vma;
+
+ VMA_ITERATOR(vmi, mm, 0);
+ for_each_vma(vmi, vma)
+ __ksm_add_vma(vma);
+}
+
+/**
+ * ksm_add_mm - Add mm to mm ksm list
+ *
+ * @mm: Pointer to mm
+ *
+ * Returns 0 on success, otherwise error code
+ */
+int ksm_add_mm(struct mm_struct *mm)
+{
+ if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))
+ return -EINVAL;
+ if (test_bit(MMF_VM_MERGEABLE, &mm->flags))
+ return -EINVAL;
+
+ return __ksm_enter(mm, MMF_VM_MERGE_ANY);
+}
+
int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
unsigned long end, int advice, unsigned long *vm_flags)
{
@@ -2579,28 +2661,13 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
switch (advice) {
case MADV_MERGEABLE:
- /*
- * Be somewhat over-protective for now!
- */
- if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
- VM_PFNMAP | VM_IO | VM_DONTEXPAND |
- VM_HUGETLB | VM_MIXEDMAP))
- return 0; /* just ignore the advice */
-
- if (vma_is_dax(vma))
+ if (vma->vm_flags & VM_MERGEABLE)
return 0;
-
-#ifdef VM_SAO
- if (*vm_flags & VM_SAO)
+ if (!vma_ksm_compatible(vma))
return 0;
-#endif
-#ifdef VM_SPARC_ADI
- if (*vm_flags & VM_SPARC_ADI)
- return 0;
-#endif
if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
- err = __ksm_enter(mm);
+ err = __ksm_enter(mm, MMF_VM_MERGEABLE);
if (err)
return err;
}
@@ -2626,7 +2693,7 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
}
EXPORT_SYMBOL_GPL(ksm_madvise);
-int __ksm_enter(struct mm_struct *mm)
+int __ksm_enter(struct mm_struct *mm, int flag)
{
struct ksm_mm_slot *mm_slot;
struct mm_slot *slot;
@@ -2659,7 +2726,7 @@ int __ksm_enter(struct mm_struct *mm)
list_add_tail(&slot->mm_node, &ksm_scan.mm_slot->slot.mm_node);
spin_unlock(&ksm_mmlist_lock);
- set_bit(MMF_VM_MERGEABLE, &mm->flags);
+ set_bit(flag, &mm->flags);
mmgrab(mm);
if (needs_wakeup)
@@ -2668,7 +2735,7 @@ int __ksm_enter(struct mm_struct *mm)
return 0;
}
-void __ksm_exit(struct mm_struct *mm)
+void __ksm_exit(struct mm_struct *mm, int flag)
{
struct ksm_mm_slot *mm_slot;
struct mm_slot *slot;
@@ -2700,7 +2767,7 @@ void __ksm_exit(struct mm_struct *mm)
if (easy_to_free) {
mm_slot_free(mm_slot_cache, mm_slot);
- clear_bit(MMF_VM_MERGEABLE, &mm->flags);
+ clear_bit(flag, &mm->flags);
mmdrop(mm);
} else if (mm_slot) {
mmap_write_lock(mm);
diff --git a/mm/mmap.c b/mm/mmap.c
index 740b54be3ed4..483e182e0b9d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -46,6 +46,7 @@
#include <linux/pkeys.h>
#include <linux/oom.h>
#include <linux/sched/mm.h>
+#include <linux/ksm.h>
#include <linux/uaccess.h>
#include <asm/cacheflush.h>
@@ -2213,6 +2214,8 @@ int __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
/* vma_complete stores the new vma */
vma_complete(&vp, vmi, vma->vm_mm);
+ ksm_add_vma(new);
+
Splitting a VMA shouldn't modify VM_MERGEABLE, so I assume this is not
required?
/* Success. */
if (new_below)
vma_next(vmi);
@@ -2664,6 +2667,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
if (file && vm_flags & VM_SHARED)
mapping_unmap_writable(file->f_mapping);
file = vma->vm_file;
+ ksm_add_vma(vma);
expanded:
perf_event_mmap(vma);
@@ -2936,6 +2940,7 @@ static int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,
goto mas_store_fail;
mm->map_count++;
+ ksm_add_vma(vma);
out:
perf_event_mmap(vma);
mm->total_vm += len >> PAGE_SHIFT;
@@ -3180,6 +3185,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
if (vma_link(mm, new_vma))
goto out_vma_link;
*need_rmap_locks = false;
+ ksm_add_vma(new_vma);
Copying shouldn't modify VM_MERGEABLE, so I think this is not required?
}
validate_mm_mt(mm);
return new_vma;
@@ -3356,6 +3362,7 @@ static struct vm_area_struct *__install_special_mapping(
vm_stat_account(mm, vma->vm_flags, len >> PAGE_SHIFT);
perf_event_mmap(vma);
+ ksm_add_vma(vma);
IIUC, special mappings will never be considered a reasonable target for
KSM (especially, because at least VM_DONTEXPAND is always set).
I think you can just drop this call.
--
Thanks,
David / dhildenb
