[RFC PATCH v2 00/19] mm: process/cgroup ksm support

[RFC PATCH v2 00/19] mm: process/cgroup ksm support

[Stefan Roesch]

So far KSM can only be enabled by calling madvise for memory regions. What is
required to enable KSM for more workloads is to enable / disable it at the
process / cgroup level.

Use case:
The madvise call is not available in the programming language. An example for
this are programs with forked workloads using a garbage collected language without
pointers. In such a language madvise cannot be made available.

In addition the addresses of objects get moved around as they are garbage
collected. KSM sharing needs to be enabled "from the outside" for these type of
workloads.

Experiments with using UKSM have shown a capacity increase of around 20%.


1. New options for prctl system command
This patch series adds two new options to the prctl system call. The first
one allows to enable KSM at the process level and the second one to query the
setting.

The setting will be inherited by child processes.

With the above setting, KSM can be enabled for the seed process of a cgroup
and all processes in the cgroup will inherit the setting.

2. Changes to KSM processing
When KSM is enabled at the process level, the KSM code will iterate over all
the VMA's and enable KSM for the eligible VMA's.

When forking a process that has KSM enabled, the setting will be inherited by
the new child process.

In addition when KSM is disabled for a process, KSM will be disabled for the
VMA's where KSM has been enabled.

3. Add general_profit metric
The general_profit metric of KSM is specified in the documentation, but not
calculated. This adds the general profit metric to /sys/kernel/debug/mm/ksm.

4. Add more metrics to ksm_stat
This adds the process profit and ksm type metric to /proc/<pid>/ksm_stat.

5. Add more tests to ksm_tests
This adds an option to specify the merge type to the ksm_tests. This allows to
test madvise and prctl KSM. It also adds a new option to query if prctl KSM has
been enabled. It adds a fork test to verify that the KSM process setting is
inherited by client processes.


Changes:
- V2:
  - Added use cases to the cover letter
  - Removed the tracing patch from the patch series and posted it as an
    individual patch
  - Refreshed repo



Stefan Roesch (19):
  mm: add new flag to enable ksm per process
  mm: add flag to __ksm_enter
  mm: add flag to __ksm_exit call
  mm: invoke madvise for all vmas in scan_get_next_rmap_item
  mm: support disabling of ksm for a process
  mm: add new prctl option to get and set ksm for a process
  mm: split off pages_volatile function
  mm: expose general_profit metric
  docs: document general_profit sysfs knob
  mm: calculate ksm process profit metric
  mm: add ksm_merge_type() function
  mm: expose ksm process profit metric in ksm_stat
  mm: expose ksm merge type in ksm_stat
  docs: document new procfs ksm knobs
  tools: add new prctl flags to prctl in tools dir
  selftests/vm: add KSM prctl merge test
  selftests/vm: add KSM get merge type test
  selftests/vm: add KSM fork test
  selftests/vm: add two functions for debugging merge outcome

 Documentation/ABI/testing/sysfs-kernel-mm-ksm |   8 +
 Documentation/admin-guide/mm/ksm.rst          |   8 +-
 fs/proc/base.c                                |   5 +
 include/linux/ksm.h                           |  19 +-
 include/linux/sched/coredump.h                |   1 +
 include/uapi/linux/prctl.h                    |   2 +
 kernel/sys.c                                  |  29 ++
 mm/ksm.c                                      | 114 +++++++-
 tools/include/uapi/linux/prctl.h              |   2 +
 tools/testing/selftests/mm/Makefile           |   3 +-
 tools/testing/selftests/mm/ksm_tests.c        | 254 +++++++++++++++---
 11 files changed, 389 insertions(+), 56 deletions(-)


base-commit: 234a68e24b120b98875a8b6e17a9dead277be16a
-- 
2.30.2

[RFC PATCH v2 01/19] mm: add new flag to enable ksm per process

[Stefan Roesch]

This introduces the new flag MMF_VM_MERGE_ANY flag. When this flag is
set, kernel samepage merging (ksm) gets enabled for all vma's of a
process.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 include/linux/sched/coredump.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h
index 0e17ae7fbfd3..0ee96ea7a0e9 100644
--- a/include/linux/sched/coredump.h
+++ b/include/linux/sched/coredump.h
@@ -90,4 +90,5 @@ static inline int get_dumpable(struct mm_struct *mm)
 #define MMF_INIT_MASK		(MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\
 				 MMF_DISABLE_THP_MASK | MMF_HAS_MDWE_MASK)
 
+#define MMF_VM_MERGE_ANY	29
 #endif /* _LINUX_SCHED_COREDUMP_H */
-- 
2.30.2

[RFC PATCH v2 02/19] mm: add flag to __ksm_enter

[Stefan Roesch]

This change adds the flag parameter to __ksm_enter. This allows to
distinguish if ksm was called by prctl or madvise.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 include/linux/ksm.h | 6 ++++--
 mm/ksm.c            | 9 +++++----
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 7e232ba59b86..50e6b56092f3 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -18,13 +18,15 @@
 #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_enter(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_enter(mm, MMF_VM_MERGE_ANY);
 	if (test_bit(MMF_VM_MERGEABLE, &oldmm->flags))
-		return __ksm_enter(mm);
+		return __ksm_enter(mm, MMF_VM_MERGEABLE);
 	return 0;
 }
 
diff --git a/mm/ksm.c b/mm/ksm.c
index 56808e3bfd19..afc0980592af 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2595,8 +2595,9 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
 			return 0;
 #endif
 
-		if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
-			err = __ksm_enter(mm);
+		if (!test_bit(MMF_VM_MERGEABLE, &mm->flags) &&
+		    !test_bit(MMF_VM_MERGE_ANY, &mm->flags)) {
+			err = __ksm_enter(mm, MMF_VM_MERGEABLE);
 			if (err)
 				return err;
 		}
@@ -2622,7 +2623,7 @@ 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;
@@ -2655,7 +2656,7 @@ 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)
-- 
2.30.2

[RFC PATCH v2 03/19] mm: add flag to __ksm_exit call

[Stefan Roesch]

This adds the flag parameter to the __ksm_exit() call. This allows to
distinguish if this call is for an prctl or madvise invocation.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 include/linux/ksm.h | 8 +++++---
 mm/ksm.c            | 8 ++++++--
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 50e6b56092f3..d38a05a36298 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -18,8 +18,8 @@
 #ifdef CONFIG_KSM
 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
 		unsigned long end, int advice, unsigned long *vm_flags);
-void __ksm_exit(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)
 {
@@ -32,8 +32,10 @@ static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
 
 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);
 }
 
 /*
diff --git a/mm/ksm.c b/mm/ksm.c
index afc0980592af..3597ae52fe7b 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2665,12 +2665,16 @@ int __ksm_enter(struct mm_struct *mm, int flag)
 	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;
 	int easy_to_free = 0;
 
+	if (!(current->flags & PF_EXITING) && flag == MMF_VM_MERGE_ANY &&
+	    test_bit(MMF_VM_MERGE_ANY, &mm->flags))
+		clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
+
 	/*
 	 * This process is exiting: if it's straightforward (as is the
 	 * case when ksmd was never running), free mm_slot immediately.
@@ -2697,7 +2701,7 @@ 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);
-- 
2.30.2

[RFC PATCH v2 04/19] mm: invoke madvise for all vmas in scan_get_next_rmap_item

[Stefan Roesch]

If the new flag MMF_VM_MERGE_ANY has been set for a process, iterate
over all the vmas and enable ksm if possible. For the vmas that can be
ksm enabled this is only done once.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 mm/ksm.c | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 3597ae52fe7b..efd8d3804de3 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1063,6 +1063,7 @@ 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);
@@ -2329,6 +2330,17 @@ static struct ksm_rmap_item *get_next_rmap_item(struct ksm_mm_slot *mm_slot,
 	return rmap_item;
 }
 
+static bool vma_ksm_mergeable(struct vm_area_struct *vma)
+{
+	if (vma->vm_flags & VM_MERGEABLE)
+		return true;
+
+	if (test_bit(MMF_VM_MERGE_ANY, &vma->vm_mm->flags))
+		return true;
+
+	return false;
+}
+
 static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
 {
 	struct mm_struct *mm;
@@ -2405,8 +2417,20 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
 		goto no_vmas;
 
 	for_each_vma(vmi, vma) {
-		if (!(vma->vm_flags & VM_MERGEABLE))
+		if (!vma_ksm_mergeable(vma))
 			continue;
+		if (!(vma->vm_flags & VM_MERGEABLE)) {
+			unsigned long flags = vma->vm_flags;
+
+			/* madvise failed, use next vma */
+			if (ksm_madvise(vma, vma->vm_start, vma->vm_end, MADV_MERGEABLE, &flags))
+				continue;
+			/* vma, not supported as being mergeable */
+			if (!(flags & VM_MERGEABLE))
+				continue;
+
+			vm_flags_set(vma, VM_MERGEABLE);
+		}
 		if (ksm_scan.address < vma->vm_start)
 			ksm_scan.address = vma->vm_start;
 		if (!vma->anon_vma)
@@ -2491,6 +2515,7 @@ 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 {
-- 
2.30.2

[RFC PATCH v2 05/19] mm: support disabling of ksm for a process

[Stefan Roesch]

This adds the ability to disable ksm for a process if ksm has been
enabled for the process.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 mm/ksm.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index efd8d3804de3..23d6944f78ad 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2690,6 +2690,27 @@ int __ksm_enter(struct mm_struct *mm, int flag)
 	return 0;
 }
 
+static void unmerge_vmas(struct mm_struct *mm)
+{
+	struct vm_area_struct *vma;
+	struct vma_iterator vmi;
+
+	vma_iter_init(&vmi, mm, 0);
+
+	mmap_read_lock(mm);
+	for_each_vma(vmi, vma) {
+		if (vma->vm_flags & VM_MERGEABLE) {
+			unsigned long flags = vma->vm_flags;
+
+			if (ksm_madvise(vma, vma->vm_start, vma->vm_end, MADV_UNMERGEABLE, &flags))
+				continue;
+
+			vm_flags_clear(vma, VM_MERGEABLE);
+		}
+	}
+	mmap_read_unlock(mm);
+}
+
 void __ksm_exit(struct mm_struct *mm, int flag)
 {
 	struct ksm_mm_slot *mm_slot;
@@ -2697,8 +2718,10 @@ void __ksm_exit(struct mm_struct *mm, int flag)
 	int easy_to_free = 0;
 
 	if (!(current->flags & PF_EXITING) && flag == MMF_VM_MERGE_ANY &&
-	    test_bit(MMF_VM_MERGE_ANY, &mm->flags))
+		test_bit(MMF_VM_MERGE_ANY, &mm->flags)) {
 		clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
+		unmerge_vmas(mm);
+	}
 
 	/*
 	 * This process is exiting: if it's straightforward (as is the
-- 
2.30.2

[RFC PATCH v2 06/19] mm: add new prctl option to get and set ksm for a process

[Stefan Roesch]

This adds two new options to the prctl system call
- enable ksm for all vmas of a process (if the vmas support it).
- query if ksm has been enabled for a process.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 include/uapi/linux/prctl.h |  2 ++
 kernel/sys.c               | 29 +++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

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/sys.c b/kernel/sys.c
index b3cab94545ed..495bab3ed2ad 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>
@@ -2659,6 +2660,34 @@ 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 (!capable(CAP_SYS_RESOURCE))
+			return -EPERM;
+
+		if (arg2) {
+			if (mmap_write_lock_killable(me->mm))
+				return -EINTR;
+
+			if (test_bit(MMF_VM_MERGEABLE, &me->mm->flags))
+				error = -EINVAL;
+			else if (!test_bit(MMF_VM_MERGE_ANY, &me->mm->flags))
+				error = __ksm_enter(me->mm, MMF_VM_MERGE_ANY);
+			mmap_write_unlock(me->mm);
+		} else {
+			__ksm_exit(me->mm, MMF_VM_MERGE_ANY);
+		}
+		break;
+	case PR_GET_MEMORY_MERGE:
+		if (!capable(CAP_SYS_RESOURCE))
+			return -EPERM;
+
+		if (arg2 || arg3 || arg4 || arg5)
+			return -EINVAL;
+
+		error = !!test_bit(MMF_VM_MERGE_ANY, &me->mm->flags);
+		break;
+#endif
 	default:
 		error = -EINVAL;
 		break;
-- 
2.30.2

[RFC PATCH v2 07/19] mm: split off pages_volatile function

[Stefan Roesch]

This splits off the pages_volatile function. The next patch will use
this function.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 mm/ksm.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 23d6944f78ad..7f3b28b7536e 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -3271,8 +3271,7 @@ static ssize_t pages_unshared_show(struct kobject *kobj,
 }
 KSM_ATTR_RO(pages_unshared);
 
-static ssize_t pages_volatile_show(struct kobject *kobj,
-				   struct kobj_attribute *attr, char *buf)
+static long pages_volatile(void)
 {
 	long ksm_pages_volatile;
 
@@ -3284,7 +3283,14 @@ static ssize_t pages_volatile_show(struct kobject *kobj,
 	 */
 	if (ksm_pages_volatile < 0)
 		ksm_pages_volatile = 0;
-	return sysfs_emit(buf, "%ld\n", ksm_pages_volatile);
+
+	return ksm_pages_volatile;
+}
+
+static ssize_t pages_volatile_show(struct kobject *kobj,
+				   struct kobj_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%ld\n", pages_volatile());
 }
 KSM_ATTR_RO(pages_volatile);
 
-- 
2.30.2

[RFC PATCH v2 08/19] mm: expose general_profit metric

[Stefan Roesch]

The documentation mentions a general profit metric, however this metric
is not calculated. In addition the formula depends on the size of
internal structures, which makes it more difficult for an administrator
to make the calculation. Adding the metric for a better user experience.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 mm/ksm.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/mm/ksm.c b/mm/ksm.c
index 7f3b28b7536e..a0b4611112c0 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -3301,6 +3301,21 @@ static ssize_t zero_pages_sharing_show(struct kobject *kobj,
 }
 KSM_ATTR_RO(zero_pages_sharing);
 
+static ssize_t general_profit_show(struct kobject *kobj,
+				   struct kobj_attribute *attr, char *buf)
+{
+	long general_profit;
+	long all_rmap_items;
+
+	all_rmap_items = ksm_max_page_sharing + ksm_pages_shared +
+				ksm_pages_unshared + pages_volatile();
+	general_profit = ksm_pages_sharing * PAGE_SIZE -
+				all_rmap_items * sizeof(struct ksm_rmap_item);
+
+	return sysfs_emit(buf, "%ld\n", general_profit);
+}
+KSM_ATTR_RO(general_profit);
+
 static ssize_t stable_node_dups_show(struct kobject *kobj,
 				     struct kobj_attribute *attr, char *buf)
 {
@@ -3366,6 +3381,7 @@ static struct attribute *ksm_attrs[] = {
 	&stable_node_dups_attr.attr,
 	&stable_node_chains_prune_millisecs_attr.attr,
 	&use_zero_pages_attr.attr,
+	&general_profit_attr.attr,
 	NULL,
 };
 
-- 
2.30.2

[RFC PATCH v2 09/19] docs: document general_profit sysfs knob

[Stefan Roesch]

Document general_progit knob.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 Documentation/ABI/testing/sysfs-kernel-mm-ksm | 8 ++++++++
 Documentation/admin-guide/mm/ksm.rst          | 2 ++
 2 files changed, 10 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-ksm b/Documentation/ABI/testing/sysfs-kernel-mm-ksm
index d244674a9480..7768e90f7a8f 100644
--- a/Documentation/ABI/testing/sysfs-kernel-mm-ksm
+++ b/Documentation/ABI/testing/sysfs-kernel-mm-ksm
@@ -51,3 +51,11 @@ Description:	Control merging pages across different NUMA nodes.
 
 		When it is set to 0 only pages from the same node are merged,
 		otherwise pages from all nodes can be merged together (default).
+
+What:		/sys/kernel/mm/ksm/general_profit
+Date:		January 2023
+KernelVersion:  6.1
+Contact:	Linux memory management mailing list <linux-mm@kvack.org>
+Description:	Measure how effective KSM is.
+		general_profit: how effective is KSM. The formula for the
+		calculation is in Documentation/admin-guide/mm/ksm.rst.
diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst
index f160f9487a90..5c4daf44d79d 100644
--- a/Documentation/admin-guide/mm/ksm.rst
+++ b/Documentation/admin-guide/mm/ksm.rst
@@ -159,6 +159,8 @@ stable_node_chains_prune_millisecs
 
 The effectiveness of KSM and MADV_MERGEABLE is shown in ``/sys/kernel/mm/ksm/``:
 
+general_profit
+        how effective is KSM. The calculation is explained below.
 pages_shared
         how many shared pages are being used
 pages_sharing
-- 
2.30.2

Re: [RFC PATCH v2 09/19] docs: document general_profit sysfs knob

[Bagas Sanjaya]

On 2/11/23 04:50, Stefan Roesch wrote:
> Document general_progit knob.

Book about Git :); it should have been general_profit.
 
> diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-ksm b/Documentation/ABI/testing/sysfs-kernel-mm-ksm
> index d244674a9480..7768e90f7a8f 100644
> --- a/Documentation/ABI/testing/sysfs-kernel-mm-ksm
> +++ b/Documentation/ABI/testing/sysfs-kernel-mm-ksm
> @@ -51,3 +51,11 @@ Description:	Control merging pages across different NUMA nodes.
>  
>  		When it is set to 0 only pages from the same node are merged,
>  		otherwise pages from all nodes can be merged together (default).
> +
> +What:		/sys/kernel/mm/ksm/general_profit
> +Date:		January 2023
> +KernelVersion:  6.1
> +Contact:	Linux memory management mailing list <linux-mm@kvack.org>
> +Description:	Measure how effective KSM is.
> +		general_profit: how effective is KSM. The formula for the
> +		calculation is in Documentation/admin-guide/mm/ksm.rst.
> diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst
> index f160f9487a90..5c4daf44d79d 100644
> --- a/Documentation/admin-guide/mm/ksm.rst
> +++ b/Documentation/admin-guide/mm/ksm.rst
> @@ -159,6 +159,8 @@ stable_node_chains_prune_millisecs
>  
>  The effectiveness of KSM and MADV_MERGEABLE is shown in ``/sys/kernel/mm/ksm/``:
>  
> +general_profit
> +        how effective is KSM. The calculation is explained below.
>  pages_shared
>          how many shared pages are being used
>  pages_sharing

LGTM, thanks!

Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>

-- 
An old man doll... just what I always wanted! - Clara

Re: [RFC PATCH v2 09/19] docs: document general_profit sysfs knob

[Stefan Roesch]

Bagas Sanjaya <bagasdotme@gmail.com> writes:

> On 2/11/23 04:50, Stefan Roesch wrote:
>> Document general_progit knob.
>
> Book about Git :); it should have been general_profit.
>

Thanks, Fixed.

>> diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-ksm b/Documentation/ABI/testing/sysfs-kernel-mm-ksm
>> index d244674a9480..7768e90f7a8f 100644
>> --- a/Documentation/ABI/testing/sysfs-kernel-mm-ksm
>> +++ b/Documentation/ABI/testing/sysfs-kernel-mm-ksm
>> @@ -51,3 +51,11 @@ Description:	Control merging pages across different NUMA nodes.
>>
>>  		When it is set to 0 only pages from the same node are merged,
>>  		otherwise pages from all nodes can be merged together (default).
>> +
>> +What:		/sys/kernel/mm/ksm/general_profit
>> +Date:		January 2023
>> +KernelVersion:  6.1
>> +Contact:	Linux memory management mailing list <linux-mm@kvack.org>
>> +Description:	Measure how effective KSM is.
>> +		general_profit: how effective is KSM. The formula for the
>> +		calculation is in Documentation/admin-guide/mm/ksm.rst.
>> diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst
>> index f160f9487a90..5c4daf44d79d 100644
>> --- a/Documentation/admin-guide/mm/ksm.rst
>> +++ b/Documentation/admin-guide/mm/ksm.rst
>> @@ -159,6 +159,8 @@ stable_node_chains_prune_millisecs
>>
>>  The effectiveness of KSM and MADV_MERGEABLE is shown in ``/sys/kernel/mm/ksm/``:
>>
>> +general_profit
>> +        how effective is KSM. The calculation is explained below.
>>  pages_shared
>>          how many shared pages are being used
>>  pages_sharing
>
> LGTM, thanks!
>
> Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>

[RFC PATCH v2 10/19] mm: calculate ksm process profit metric

[Stefan Roesch]

The ksm documentation mentions the process profit metric and how to
calculate it. This adds the calculation of the metric.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 include/linux/ksm.h | 4 ++++
 mm/ksm.c            | 8 ++++++++
 2 files changed, 12 insertions(+)

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index d38a05a36298..a18cd03efcfb 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -55,6 +55,10 @@ struct page *ksm_might_need_to_copy(struct page *page,
 void rmap_walk_ksm(struct folio *folio, struct rmap_walk_control *rwc);
 void folio_migrate_ksm(struct folio *newfolio, struct folio *folio);
 
+#ifdef CONFIG_PROC_FS
+long ksm_process_profit(struct mm_struct *);
+#endif /* CONFIG_PROC_FS */
+
 #else  /* !CONFIG_KSM */
 
 static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
diff --git a/mm/ksm.c b/mm/ksm.c
index a0b4611112c0..b3db29605303 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -3024,6 +3024,14 @@ static void wait_while_offlining(void)
 }
 #endif /* CONFIG_MEMORY_HOTREMOVE */
 
+#ifdef CONFIG_PROC_FS
+long ksm_process_profit(struct mm_struct *mm)
+{
+	return (long)mm->ksm_merging_pages * PAGE_SIZE -
+		mm->ksm_rmap_items * sizeof(struct ksm_rmap_item);
+}
+#endif /* CONFIG_PROC_FS */
+
 #ifdef CONFIG_SYSFS
 /*
  * This all compiles without CONFIG_SYSFS, but is a waste of space.
-- 
2.30.2

[RFC PATCH v2 11/19] mm: add ksm_merge_type() function

[Stefan Roesch]

This adds the ksm_merge_type function. The function returns the merge
type for the process. For madvise it returns "madvise", for prctl it
returns "process" and otherwise it returns "none".

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 include/linux/ksm.h |  1 +
 mm/ksm.c            | 11 +++++++++++
 2 files changed, 12 insertions(+)

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index a18cd03efcfb..d5f69f18ee5a 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -57,6 +57,7 @@ void folio_migrate_ksm(struct folio *newfolio, struct folio *folio);
 
 #ifdef CONFIG_PROC_FS
 long ksm_process_profit(struct mm_struct *);
+const char *ksm_merge_type(struct mm_struct *mm);
 #endif /* CONFIG_PROC_FS */
 
 #else  /* !CONFIG_KSM */
diff --git a/mm/ksm.c b/mm/ksm.c
index b3db29605303..3121bc0f48f3 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -3030,6 +3030,17 @@ long ksm_process_profit(struct mm_struct *mm)
 	return (long)mm->ksm_merging_pages * PAGE_SIZE -
 		mm->ksm_rmap_items * sizeof(struct ksm_rmap_item);
 }
+
+/* Return merge type name as string. */
+const char *ksm_merge_type(struct mm_struct *mm)
+{
+	if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))
+		return "process";
+	else if (test_bit(MMF_VM_MERGEABLE, &mm->flags))
+		return "madvise";
+	else
+		return "none";
+}
 #endif /* CONFIG_PROC_FS */
 
 #ifdef CONFIG_SYSFS
-- 
2.30.2

[RFC PATCH v2 12/19] mm: expose ksm process profit metric in ksm_stat

[Stefan Roesch]

This exposes the ksm process profit metric in /proc/<pid>/ksm_stat.
The documentation mentions the formula for the ksm process profit
metric, however it does not calculate it. In addition the formula
depends on the size of internal structures. So it makes sense to expose
it.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 fs/proc/base.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index ac9ebe972be0..fb9567bc42a4 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -96,6 +96,7 @@
 #include <linux/time_namespace.h>
 #include <linux/resctrl.h>
 #include <linux/cn_proc.h>
+#include <linux/ksm.h>
 #include <trace/events/oom.h>
 #include "internal.h"
 #include "fd.h"
@@ -3208,6 +3209,8 @@ static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns,
 	if (mm) {
 		seq_printf(m, "ksm_rmap_items %lu\n", mm->ksm_rmap_items);
 		seq_printf(m, "zero_pages_sharing %lu\n", mm->ksm_zero_pages_sharing);
+		seq_printf(m, "ksm_merging_pages %lu\n", mm->ksm_merging_pages);
+		seq_printf(m, "ksm_process_profit %ld\n", ksm_process_profit(mm));
 		mmput(mm);
 	}
 
-- 
2.30.2

[RFC PATCH v2 13/19] mm: expose ksm merge type in ksm_stat

[Stefan Roesch]

This exposes the ksm process type in /proc/<pid>/ksm_stat. The name of
the value is ksm_merge_type.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 fs/proc/base.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index fb9567bc42a4..45749051e53b 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3200,6 +3200,7 @@ static int proc_pid_ksm_merging_pages(struct seq_file *m, struct pid_namespace *
 
 	return 0;
 }
+
 static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns,
 				struct pid *pid, struct task_struct *task)
 {
@@ -3210,6 +3211,7 @@ static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns,
 		seq_printf(m, "ksm_rmap_items %lu\n", mm->ksm_rmap_items);
 		seq_printf(m, "zero_pages_sharing %lu\n", mm->ksm_zero_pages_sharing);
 		seq_printf(m, "ksm_merging_pages %lu\n", mm->ksm_merging_pages);
+		seq_printf(m, "ksm_merge_type %s\n", ksm_merge_type(mm));
 		seq_printf(m, "ksm_process_profit %ld\n", ksm_process_profit(mm));
 		mmput(mm);
 	}
-- 
2.30.2

[RFC PATCH v2 14/19] docs: document new procfs ksm knobs

[Stefan Roesch]

Document both ksm_process_profit and ksm_merge_type proc settings.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
Reviewed-By: Bagas Sanjaya <bagasdotme@gmail.com>
---
 Documentation/admin-guide/mm/ksm.rst | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst
index 5c4daf44d79d..34f1d0396eee 100644
--- a/Documentation/admin-guide/mm/ksm.rst
+++ b/Documentation/admin-guide/mm/ksm.rst
@@ -218,7 +218,8 @@ several times, which are unprofitable memory consumed.
 			  ksm_rmap_items * sizeof(rmap_item).
 
    where ksm_merging_pages is shown under the directory ``/proc/<pid>/``,
-   and ksm_rmap_items is shown in ``/proc/<pid>/ksm_stat``.
+   and ksm_rmap_items is shown in ``/proc/<pid>/ksm_stat``. The process profit
+   is also shown in ``/proc/<pid>/ksm_stat`` as ksm_process_profit.
 
 From the perspective of application, a high ratio of ``ksm_rmap_items`` to
 ``ksm_merging_pages`` means a bad madvise-applied policy, so developers or
@@ -229,6 +230,9 @@ so if the ``ksm_rmap_items/ksm_merging_pages`` ratio exceeds 64 on 64-bit CPU
 or exceeds 128 on 32-bit CPU, then the app's madvise policy should be dropped,
 because the ksm profit is approximately zero or negative.
 
+The ksm_merge_type in ``/proc/<pid>/ksm_stat`` shows the merge type of the
+process. Valid values are ``none``, ``madvise`` and ``process``.
+
 Monitoring KSM events
 =====================
 
-- 
2.30.2

Re: [RFC PATCH v2 14/19] docs: document new procfs ksm knobs

[Bagas Sanjaya]

On 2/11/23 04:50, Stefan Roesch wrote:
> diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst
> index 5c4daf44d79d..34f1d0396eee 100644
> --- a/Documentation/admin-guide/mm/ksm.rst
> +++ b/Documentation/admin-guide/mm/ksm.rst
> @@ -218,7 +218,8 @@ several times, which are unprofitable memory consumed.
>  			  ksm_rmap_items * sizeof(rmap_item).
>  
>     where ksm_merging_pages is shown under the directory ``/proc/<pid>/``,
> -   and ksm_rmap_items is shown in ``/proc/<pid>/ksm_stat``.
> +   and ksm_rmap_items is shown in ``/proc/<pid>/ksm_stat``. The process profit
> +   is also shown in ``/proc/<pid>/ksm_stat`` as ksm_process_profit.
>  
>  From the perspective of application, a high ratio of ``ksm_rmap_items`` to
>  ``ksm_merging_pages`` means a bad madvise-applied policy, so developers or
> @@ -229,6 +230,9 @@ so if the ``ksm_rmap_items/ksm_merging_pages`` ratio exceeds 64 on 64-bit CPU
>  or exceeds 128 on 32-bit CPU, then the app's madvise policy should be dropped,
>  because the ksm profit is approximately zero or negative.
>  
> +The ksm_merge_type in ``/proc/<pid>/ksm_stat`` shows the merge type of the
> +process. Valid values are ``none``, ``madvise`` and ``process``.
> +
>  Monitoring KSM events
>  =====================
>  

LGTM, thanks!

Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>

-- 
An old man doll... just what I always wanted! - Clara

[RFC PATCH v2 15/19] tools: add new prctl flags to prctl in tools dir

[Stefan Roesch]

This adds the new prctl flags to the include file prct.h in the tools
directory. This makes sure they are available for testing.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 tools/include/uapi/linux/prctl.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/include/uapi/linux/prctl.h b/tools/include/uapi/linux/prctl.h
index a5e06dcbba13..e4c629c1f1b0 100644
--- a/tools/include/uapi/linux/prctl.h
+++ b/tools/include/uapi/linux/prctl.h
@@ -284,4 +284,6 @@ 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 */
-- 
2.30.2

[RFC PATCH v2 16/19] selftests/vm: add KSM prctl merge test

[Stefan Roesch]

This adds the -t option to the ksm_tests program. The -t flag allows to
specify if it should use madvise or prctl ksm merging.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 tools/testing/selftests/mm/Makefile    |   3 +-
 tools/testing/selftests/mm/ksm_tests.c | 116 +++++++++++++++++--------
 2 files changed, 80 insertions(+), 39 deletions(-)

diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index d90cdc06aa59..507cb22bdebd 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -29,7 +29,8 @@ MACHINE ?= $(shell echo $(uname_M) | sed -e 's/aarch64.*/arm64/' -e 's/ppc64.*/p
 # LDLIBS.
 MAKEFLAGS += --no-builtin-rules
 
-CFLAGS = -Wall -I $(top_srcdir) -I $(top_srcdir)/usr/include $(EXTRA_CFLAGS) $(KHDR_INCLUDES)
+CFLAGS = -Wall -I $(top_srcdir)/tools/include/uapi
+CFLAGS += -I $(top_srcdir) -I $(top_srcdir)/usr/include $(EXTRA_CFLAGS) $(KHDR_INCLUDES)
 LDLIBS = -lrt -lpthread
 TEST_GEN_FILES = cow
 TEST_GEN_FILES += compaction_test
diff --git a/tools/testing/selftests/mm/ksm_tests.c b/tools/testing/selftests/mm/ksm_tests.c
index f9eb4d67e0dd..386a0929c8a3 100644
--- a/tools/testing/selftests/mm/ksm_tests.c
+++ b/tools/testing/selftests/mm/ksm_tests.c
@@ -1,6 +1,8 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include <sys/mman.h>
+#include <sys/prctl.h>
+#include <sys/wait.h>
 #include <stdbool.h>
 #include <time.h>
 #include <string.h>
@@ -21,6 +23,7 @@
 #define KSM_PROT_STR_DEFAULT "rw"
 #define KSM_USE_ZERO_PAGES_DEFAULT false
 #define KSM_MERGE_ACROSS_NODES_DEFAULT true
+#define KSM_MERGE_TYPE_DEFAULT 0
 #define MB (1ul << 20)
 
 struct ksm_sysfs {
@@ -33,6 +36,12 @@ struct ksm_sysfs {
 	unsigned long use_zero_pages;
 };
 
+enum ksm_merge_type {
+	KSM_MERGE_MADVISE,
+	KSM_MERGE_PRCTL,
+	KSM_MERGE_LAST = KSM_MERGE_PRCTL
+};
+
 enum ksm_test_name {
 	CHECK_KSM_MERGE,
 	CHECK_KSM_UNMERGE,
@@ -129,6 +138,10 @@ static void print_help(void)
 	printf(" -m: change merge_across_nodes tunable\n"
 	       "     Default: %d\n", KSM_MERGE_ACROSS_NODES_DEFAULT);
 	printf(" -s: the size of duplicated memory area (in MiB)\n");
+	printf(" -t: KSM merge type\n"
+	       "     Default: 0\n"
+	       "     0: madvise merging\n"
+	       "     1: prctl merging\n");
 
 	exit(0);
 }
@@ -176,12 +189,21 @@ static int ksm_do_scan(int scan_count, struct timespec start_time, int timeout)
 	return 0;
 }
 
-static int ksm_merge_pages(void *addr, size_t size, struct timespec start_time, int timeout)
+static int ksm_merge_pages(int merge_type, void *addr, size_t size,
+			struct timespec start_time, int timeout)
 {
-	if (madvise(addr, size, MADV_MERGEABLE)) {
-		perror("madvise");
-		return 1;
+	if (merge_type == KSM_MERGE_MADVISE) {
+		if (madvise(addr, size, MADV_MERGEABLE)) {
+			perror("madvise");
+			return 1;
+		}
+	} else if (merge_type == KSM_MERGE_PRCTL) {
+		if (prctl(PR_SET_MEMORY_MERGE, 1)) {
+			perror("prctl");
+			return 1;
+		}
 	}
+
 	if (ksm_write_sysfs(KSM_FP("run"), 1))
 		return 1;
 
@@ -266,7 +288,8 @@ static int ksm_restore(struct ksm_sysfs *ksm_sysfs)
 	return 0;
 }
 
-static int check_ksm_merge(int mapping, int prot, long page_count, int timeout, size_t page_size)
+static int check_ksm_merge(int merge_type, int mapping, int prot,
+			long page_count, int timeout, size_t page_size)
 {
 	void *map_ptr;
 	struct timespec start_time;
@@ -281,13 +304,16 @@ static int check_ksm_merge(int mapping, int prot, long page_count, int timeout,
 	if (!map_ptr)
 		return KSFT_FAIL;
 
-	if (ksm_merge_pages(map_ptr, page_size * page_count, start_time, timeout))
+	if (ksm_merge_pages(merge_type, map_ptr, page_size * page_count, start_time, timeout))
 		goto err_out;
 
 	/* verify that the right number of pages are merged */
 	if (assert_ksm_pages_count(page_count)) {
 		printf("OK\n");
-		munmap(map_ptr, page_size * page_count);
+		if (merge_type == KSM_MERGE_MADVISE)
+			munmap(map_ptr, page_size * page_count);
+		else if (merge_type == KSM_MERGE_PRCTL)
+			prctl(PR_SET_MEMORY_MERGE, 0);
 		return KSFT_PASS;
 	}
 
@@ -297,7 +323,7 @@ static int check_ksm_merge(int mapping, int prot, long page_count, int timeout,
 	return KSFT_FAIL;
 }
 
-static int check_ksm_unmerge(int mapping, int prot, int timeout, size_t page_size)
+static int check_ksm_unmerge(int merge_type, int mapping, int prot, int timeout, size_t page_size)
 {
 	void *map_ptr;
 	struct timespec start_time;
@@ -313,7 +339,7 @@ static int check_ksm_unmerge(int mapping, int prot, int timeout, size_t page_siz
 	if (!map_ptr)
 		return KSFT_FAIL;
 
-	if (ksm_merge_pages(map_ptr, page_size * page_count, start_time, timeout))
+	if (ksm_merge_pages(merge_type, map_ptr, page_size * page_count, start_time, timeout))
 		goto err_out;
 
 	/* change 1 byte in each of the 2 pages -- KSM must automatically unmerge them */
@@ -337,8 +363,8 @@ static int check_ksm_unmerge(int mapping, int prot, int timeout, size_t page_siz
 	return KSFT_FAIL;
 }
 
-static int check_ksm_zero_page_merge(int mapping, int prot, long page_count, int timeout,
-				     bool use_zero_pages, size_t page_size)
+static int check_ksm_zero_page_merge(int merge_type, int mapping, int prot, long page_count,
+				int timeout, bool use_zero_pages, size_t page_size)
 {
 	void *map_ptr;
 	struct timespec start_time;
@@ -356,7 +382,7 @@ static int check_ksm_zero_page_merge(int mapping, int prot, long page_count, int
 	if (!map_ptr)
 		return KSFT_FAIL;
 
-	if (ksm_merge_pages(map_ptr, page_size * page_count, start_time, timeout))
+	if (ksm_merge_pages(merge_type, map_ptr, page_size * page_count, start_time, timeout))
 		goto err_out;
 
        /*
@@ -402,8 +428,8 @@ static int get_first_mem_node(void)
 	return get_next_mem_node(numa_max_node());
 }
 
-static int check_ksm_numa_merge(int mapping, int prot, int timeout, bool merge_across_nodes,
-				size_t page_size)
+static int check_ksm_numa_merge(int merge_type, int mapping, int prot, int timeout,
+				bool merge_across_nodes, size_t page_size)
 {
 	void *numa1_map_ptr, *numa2_map_ptr;
 	struct timespec start_time;
@@ -439,8 +465,8 @@ static int check_ksm_numa_merge(int mapping, int prot, int timeout, bool merge_a
 	memset(numa2_map_ptr, '*', page_size);
 
 	/* try to merge the pages */
-	if (ksm_merge_pages(numa1_map_ptr, page_size, start_time, timeout) ||
-	    ksm_merge_pages(numa2_map_ptr, page_size, start_time, timeout))
+	if (ksm_merge_pages(merge_type, numa1_map_ptr, page_size, start_time, timeout) ||
+	    ksm_merge_pages(merge_type, numa2_map_ptr, page_size, start_time, timeout))
 		goto err_out;
 
        /*
@@ -466,7 +492,8 @@ static int check_ksm_numa_merge(int mapping, int prot, int timeout, bool merge_a
 	return KSFT_FAIL;
 }
 
-static int ksm_merge_hugepages_time(int mapping, int prot, int timeout, size_t map_size)
+static int ksm_merge_hugepages_time(int merge_type, int mapping, int prot,
+				int timeout, size_t map_size)
 {
 	void *map_ptr, *map_ptr_orig;
 	struct timespec start_time, end_time;
@@ -508,7 +535,7 @@ static int ksm_merge_hugepages_time(int mapping, int prot, int timeout, size_t m
 		perror("clock_gettime");
 		goto err_out;
 	}
-	if (ksm_merge_pages(map_ptr, map_size, start_time, timeout))
+	if (ksm_merge_pages(merge_type, map_ptr, map_size, start_time, timeout))
 		goto err_out;
 	if (clock_gettime(CLOCK_MONOTONIC_RAW, &end_time)) {
 		perror("clock_gettime");
@@ -533,7 +560,7 @@ static int ksm_merge_hugepages_time(int mapping, int prot, int timeout, size_t m
 	return KSFT_FAIL;
 }
 
-static int ksm_merge_time(int mapping, int prot, int timeout, size_t map_size)
+static int ksm_merge_time(int merge_type, int mapping, int prot, int timeout, size_t map_size)
 {
 	void *map_ptr;
 	struct timespec start_time, end_time;
@@ -549,7 +576,7 @@ static int ksm_merge_time(int mapping, int prot, int timeout, size_t map_size)
 		perror("clock_gettime");
 		goto err_out;
 	}
-	if (ksm_merge_pages(map_ptr, map_size, start_time, timeout))
+	if (ksm_merge_pages(merge_type, map_ptr, map_size, start_time, timeout))
 		goto err_out;
 	if (clock_gettime(CLOCK_MONOTONIC_RAW, &end_time)) {
 		perror("clock_gettime");
@@ -574,7 +601,7 @@ static int ksm_merge_time(int mapping, int prot, int timeout, size_t map_size)
 	return KSFT_FAIL;
 }
 
-static int ksm_unmerge_time(int mapping, int prot, int timeout, size_t map_size)
+static int ksm_unmerge_time(int merge_type, int mapping, int prot, int timeout, size_t map_size)
 {
 	void *map_ptr;
 	struct timespec start_time, end_time;
@@ -589,7 +616,7 @@ static int ksm_unmerge_time(int mapping, int prot, int timeout, size_t map_size)
 		perror("clock_gettime");
 		goto err_out;
 	}
-	if (ksm_merge_pages(map_ptr, map_size, start_time, timeout))
+	if (ksm_merge_pages(merge_type, map_ptr, map_size, start_time, timeout))
 		goto err_out;
 
 	if (clock_gettime(CLOCK_MONOTONIC_RAW, &start_time)) {
@@ -621,7 +648,7 @@ static int ksm_unmerge_time(int mapping, int prot, int timeout, size_t map_size)
 	return KSFT_FAIL;
 }
 
-static int ksm_cow_time(int mapping, int prot, int timeout, size_t page_size)
+static int ksm_cow_time(int merge_type, int mapping, int prot, int timeout, size_t page_size)
 {
 	void *map_ptr;
 	struct timespec start_time, end_time;
@@ -660,7 +687,7 @@ static int ksm_cow_time(int mapping, int prot, int timeout, size_t page_size)
 		memset(map_ptr + page_size * i, '+', i / 2 + 1);
 		memset(map_ptr + page_size * (i + 1), '+', i / 2 + 1);
 	}
-	if (ksm_merge_pages(map_ptr, page_size * page_count, start_time, timeout))
+	if (ksm_merge_pages(merge_type, map_ptr, page_size * page_count, start_time, timeout))
 		goto err_out;
 
 	if (clock_gettime(CLOCK_MONOTONIC_RAW, &start_time)) {
@@ -697,6 +724,7 @@ int main(int argc, char *argv[])
 	int ret, opt;
 	int prot = 0;
 	int ksm_scan_limit_sec = KSM_SCAN_LIMIT_SEC_DEFAULT;
+	int merge_type = KSM_MERGE_TYPE_DEFAULT;
 	long page_count = KSM_PAGE_COUNT_DEFAULT;
 	size_t page_size = sysconf(_SC_PAGESIZE);
 	struct ksm_sysfs ksm_sysfs_old;
@@ -705,7 +733,7 @@ int main(int argc, char *argv[])
 	bool merge_across_nodes = KSM_MERGE_ACROSS_NODES_DEFAULT;
 	long size_MB = 0;
 
-	while ((opt = getopt(argc, argv, "ha:p:l:z:m:s:MUZNPCHD")) != -1) {
+	while ((opt = getopt(argc, argv, "ha:p:l:z:m:s:t:MUZNPCHD")) != -1) {
 		switch (opt) {
 		case 'a':
 			prot = str_to_prot(optarg);
@@ -745,6 +773,17 @@ int main(int argc, char *argv[])
 				printf("Size must be greater than 0\n");
 				return KSFT_FAIL;
 			}
+		case 't':
+			{
+				int tmp = atoi(optarg);
+
+				if (tmp < 0 || tmp > KSM_MERGE_LAST) {
+					printf("Invalid merge type\n");
+					return KSFT_FAIL;
+				}
+				merge_type = atoi(optarg);
+			}
+			break;
 		case 'M':
 			break;
 		case 'U':
@@ -795,35 +834,36 @@ int main(int argc, char *argv[])
 
 	switch (test_name) {
 	case CHECK_KSM_MERGE:
-		ret = check_ksm_merge(MAP_PRIVATE | MAP_ANONYMOUS, prot, page_count,
+		ret = check_ksm_merge(merge_type, MAP_PRIVATE | MAP_ANONYMOUS, prot, page_count,
 				      ksm_scan_limit_sec, page_size);
 		break;
 	case CHECK_KSM_UNMERGE:
-		ret = check_ksm_unmerge(MAP_PRIVATE | MAP_ANONYMOUS, prot, ksm_scan_limit_sec,
-					page_size);
+		ret = check_ksm_unmerge(merge_type, MAP_PRIVATE | MAP_ANONYMOUS, prot,
+					ksm_scan_limit_sec, page_size);
 		break;
 	case CHECK_KSM_ZERO_PAGE_MERGE:
-		ret = check_ksm_zero_page_merge(MAP_PRIVATE | MAP_ANONYMOUS, prot, page_count,
-						ksm_scan_limit_sec, use_zero_pages, page_size);
+		ret = check_ksm_zero_page_merge(merge_type, MAP_PRIVATE | MAP_ANONYMOUS, prot,
+						page_count, ksm_scan_limit_sec, use_zero_pages,
+						page_size);
 		break;
 	case CHECK_KSM_NUMA_MERGE:
-		ret = check_ksm_numa_merge(MAP_PRIVATE | MAP_ANONYMOUS, prot, ksm_scan_limit_sec,
-					   merge_across_nodes, page_size);
+		ret = check_ksm_numa_merge(merge_type, MAP_PRIVATE | MAP_ANONYMOUS, prot,
+					ksm_scan_limit_sec, merge_across_nodes, page_size);
 		break;
 	case KSM_MERGE_TIME:
 		if (size_MB == 0) {
 			printf("Option '-s' is required.\n");
 			return KSFT_FAIL;
 		}
-		ret = ksm_merge_time(MAP_PRIVATE | MAP_ANONYMOUS, prot, ksm_scan_limit_sec,
-				     size_MB);
+		ret = ksm_merge_time(merge_type, MAP_PRIVATE | MAP_ANONYMOUS, prot,
+				ksm_scan_limit_sec, size_MB);
 		break;
 	case KSM_MERGE_TIME_HUGE_PAGES:
 		if (size_MB == 0) {
 			printf("Option '-s' is required.\n");
 			return KSFT_FAIL;
 		}
-		ret = ksm_merge_hugepages_time(MAP_PRIVATE | MAP_ANONYMOUS, prot,
+		ret = ksm_merge_hugepages_time(merge_type, MAP_PRIVATE | MAP_ANONYMOUS, prot,
 				ksm_scan_limit_sec, size_MB);
 		break;
 	case KSM_UNMERGE_TIME:
@@ -831,12 +871,12 @@ int main(int argc, char *argv[])
 			printf("Option '-s' is required.\n");
 			return KSFT_FAIL;
 		}
-		ret = ksm_unmerge_time(MAP_PRIVATE | MAP_ANONYMOUS, prot,
+		ret = ksm_unmerge_time(merge_type, MAP_PRIVATE | MAP_ANONYMOUS, prot,
 				       ksm_scan_limit_sec, size_MB);
 		break;
 	case KSM_COW_TIME:
-		ret = ksm_cow_time(MAP_PRIVATE | MAP_ANONYMOUS, prot, ksm_scan_limit_sec,
-				   page_size);
+		ret = ksm_cow_time(merge_type, MAP_PRIVATE | MAP_ANONYMOUS, prot,
+				ksm_scan_limit_sec, page_size);
 		break;
 	}
 
-- 
2.30.2

[RFC PATCH v2 17/19] selftests/vm: add KSM get merge type test

[Stefan Roesch]

This adds the -G flag to the ksm_tests to query if prctl has been used
to enable ksm merging.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 tools/testing/selftests/mm/ksm_tests.c | 37 ++++++++++++++++++++++++--
 1 file changed, 35 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/mm/ksm_tests.c b/tools/testing/selftests/mm/ksm_tests.c
index 386a0929c8a3..9667cb3b8c6a 100644
--- a/tools/testing/selftests/mm/ksm_tests.c
+++ b/tools/testing/selftests/mm/ksm_tests.c
@@ -45,6 +45,7 @@ enum ksm_merge_type {
 enum ksm_test_name {
 	CHECK_KSM_MERGE,
 	CHECK_KSM_UNMERGE,
+	CHECK_KSM_GET_MERGE_TYPE,
 	CHECK_KSM_ZERO_PAGE_MERGE,
 	CHECK_KSM_NUMA_MERGE,
 	KSM_MERGE_TIME,
@@ -124,7 +125,8 @@ static void print_help(void)
 	       " -D evaluate unmerging time and speed when disabling KSM.\n"
 	       "    For this test, the size of duplicated memory area (in MiB)\n"
 	       "    must be provided using -s option\n"
-	       " -C evaluate the time required to break COW of merged pages.\n\n");
+	       " -C evaluate the time required to break COW of merged pages.\n"
+	       " -G query merge mode\n\n");
 
 	printf(" -a: specify the access protections of pages.\n"
 	       "     <prot> must be of the form [rwx].\n"
@@ -323,6 +325,31 @@ static int check_ksm_merge(int merge_type, int mapping, int prot,
 	return KSFT_FAIL;
 }
 
+static int check_ksm_get_merge_type(void)
+{
+	if (prctl(PR_SET_MEMORY_MERGE, 1)) {
+		perror("prctl set");
+		return 1;
+	}
+
+	int is_on = prctl(PR_GET_MEMORY_MERGE, 0);
+
+	if (prctl(PR_SET_MEMORY_MERGE, 0)) {
+		perror("prctl set");
+		return 1;
+	}
+
+	int is_off = prctl(PR_GET_MEMORY_MERGE, 0);
+
+	if (is_on && is_off) {
+		printf("OK\n");
+		return KSFT_PASS;
+	}
+
+	printf("Not OK\n");
+	return KSFT_FAIL;
+}
+
 static int check_ksm_unmerge(int merge_type, int mapping, int prot, int timeout, size_t page_size)
 {
 	void *map_ptr;
@@ -733,7 +760,7 @@ int main(int argc, char *argv[])
 	bool merge_across_nodes = KSM_MERGE_ACROSS_NODES_DEFAULT;
 	long size_MB = 0;
 
-	while ((opt = getopt(argc, argv, "ha:p:l:z:m:s:t:MUZNPCHD")) != -1) {
+	while ((opt = getopt(argc, argv, "ha:p:l:z:m:s:t:GMUZNPCHD")) != -1) {
 		switch (opt) {
 		case 'a':
 			prot = str_to_prot(optarg);
@@ -792,6 +819,9 @@ int main(int argc, char *argv[])
 		case 'Z':
 			test_name = CHECK_KSM_ZERO_PAGE_MERGE;
 			break;
+		case 'G':
+			test_name = CHECK_KSM_GET_MERGE_TYPE;
+			break;
 		case 'N':
 			test_name = CHECK_KSM_NUMA_MERGE;
 			break;
@@ -841,6 +871,9 @@ int main(int argc, char *argv[])
 		ret = check_ksm_unmerge(merge_type, MAP_PRIVATE | MAP_ANONYMOUS, prot,
 					ksm_scan_limit_sec, page_size);
 		break;
+	case CHECK_KSM_GET_MERGE_TYPE:
+		ret = check_ksm_get_merge_type();
+		break;
 	case CHECK_KSM_ZERO_PAGE_MERGE:
 		ret = check_ksm_zero_page_merge(merge_type, MAP_PRIVATE | MAP_ANONYMOUS, prot,
 						page_count, ksm_scan_limit_sec, use_zero_pages,
-- 
2.30.2

[RFC PATCH v2 18/19] selftests/vm: add KSM fork test

[Stefan Roesch]

Add fork test to verify that the MMF_VM_MERGE_ANY flag is inherited by
the child process.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 tools/testing/selftests/mm/ksm_tests.c | 53 +++++++++++++++++++++++++-
 1 file changed, 51 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/mm/ksm_tests.c b/tools/testing/selftests/mm/ksm_tests.c
index 9667cb3b8c6a..a0a48ac43b29 100644
--- a/tools/testing/selftests/mm/ksm_tests.c
+++ b/tools/testing/selftests/mm/ksm_tests.c
@@ -44,6 +44,7 @@ enum ksm_merge_type {
 
 enum ksm_test_name {
 	CHECK_KSM_MERGE,
+	CHECK_KSM_MERGE_FORK,
 	CHECK_KSM_UNMERGE,
 	CHECK_KSM_GET_MERGE_TYPE,
 	CHECK_KSM_ZERO_PAGE_MERGE,
@@ -126,7 +127,8 @@ static void print_help(void)
 	       "    For this test, the size of duplicated memory area (in MiB)\n"
 	       "    must be provided using -s option\n"
 	       " -C evaluate the time required to break COW of merged pages.\n"
-	       " -G query merge mode\n\n");
+	       " -G query merge mode\n"
+	       " -F evaluate that the KSM process flag is inherited\n\n");
 
 	printf(" -a: specify the access protections of pages.\n"
 	       "     <prot> must be of the form [rwx].\n"
@@ -325,6 +327,47 @@ static int check_ksm_merge(int merge_type, int mapping, int prot,
 	return KSFT_FAIL;
 }
 
+/* Verify that prctl ksm flag is inherited. */
+static int check_ksm_fork(void)
+{
+	int rc = KSFT_FAIL;
+	pid_t child_pid;
+
+	if (prctl(PR_SET_MEMORY_MERGE, 1)) {
+		perror("prctl");
+		return KSFT_FAIL;
+	}
+
+	child_pid = fork();
+	if (child_pid == 0) {
+		int is_on = prctl(PR_GET_MEMORY_MERGE, 0);
+
+		if (!is_on)
+			exit(KSFT_FAIL);
+
+		exit(KSFT_PASS);
+	}
+
+	if (child_pid < 0)
+		goto out;
+
+	if (waitpid(child_pid, &rc, 0) < 0)
+		rc = KSFT_FAIL;
+
+	if (prctl(PR_SET_MEMORY_MERGE, 0)) {
+		perror("prctl");
+		rc = KSFT_FAIL;
+	}
+
+out:
+	if (rc == KSFT_PASS)
+		printf("OK\n");
+	else
+		printf("Not OK\n");
+
+	return rc;
+}
+
 static int check_ksm_get_merge_type(void)
 {
 	if (prctl(PR_SET_MEMORY_MERGE, 1)) {
@@ -760,7 +803,7 @@ int main(int argc, char *argv[])
 	bool merge_across_nodes = KSM_MERGE_ACROSS_NODES_DEFAULT;
 	long size_MB = 0;
 
-	while ((opt = getopt(argc, argv, "ha:p:l:z:m:s:t:GMUZNPCHD")) != -1) {
+	while ((opt = getopt(argc, argv, "ha:p:l:z:m:s:t:FGMUZNPCHD")) != -1) {
 		switch (opt) {
 		case 'a':
 			prot = str_to_prot(optarg);
@@ -811,6 +854,9 @@ int main(int argc, char *argv[])
 				merge_type = atoi(optarg);
 			}
 			break;
+		case 'F':
+			test_name = CHECK_KSM_MERGE_FORK;
+			break;
 		case 'M':
 			break;
 		case 'U':
@@ -867,6 +913,9 @@ int main(int argc, char *argv[])
 		ret = check_ksm_merge(merge_type, MAP_PRIVATE | MAP_ANONYMOUS, prot, page_count,
 				      ksm_scan_limit_sec, page_size);
 		break;
+	case CHECK_KSM_MERGE_FORK:
+		ret = check_ksm_fork();
+		break;
 	case CHECK_KSM_UNMERGE:
 		ret = check_ksm_unmerge(merge_type, MAP_PRIVATE | MAP_ANONYMOUS, prot,
 					ksm_scan_limit_sec, page_size);
-- 
2.30.2

[RFC PATCH v2 19/19] selftests/vm: add two functions for debugging merge outcome

[Stefan Roesch]

This adds two functions to report the metrics in /proc/self/ksm_stat and
/sys/kernel/debug/mm/ksm.

The debugging can be enabled with the following command line:
make -C tools/testing/selftests TARGETS="vm" --keep-going \
        EXTRA_CFLAGS=-DDEBUG=1

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 tools/testing/selftests/mm/ksm_tests.c | 54 ++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

diff --git a/tools/testing/selftests/mm/ksm_tests.c b/tools/testing/selftests/mm/ksm_tests.c
index a0a48ac43b29..9fb21b982dc9 100644
--- a/tools/testing/selftests/mm/ksm_tests.c
+++ b/tools/testing/selftests/mm/ksm_tests.c
@@ -93,6 +93,55 @@ static int ksm_read_sysfs(const char *file_path, unsigned long *val)
 	return 0;
 }
 
+#ifdef DEBUG
+static void ksm_print_sysfs(void)
+{
+	unsigned long max_page_sharing, pages_sharing, pages_shared;
+	unsigned long full_scans, pages_unshared, pages_volatile;
+	unsigned long stable_node_chains, stable_node_dups;
+	long general_profit;
+
+	if (ksm_read_sysfs(KSM_FP("pages_shared"), &pages_shared) ||
+	    ksm_read_sysfs(KSM_FP("pages_sharing"), &pages_sharing) ||
+	    ksm_read_sysfs(KSM_FP("max_page_sharing"), &max_page_sharing) ||
+	    ksm_read_sysfs(KSM_FP("full_scans"), &full_scans) ||
+	    ksm_read_sysfs(KSM_FP("pages_unshared"), &pages_unshared) ||
+	    ksm_read_sysfs(KSM_FP("pages_volatile"), &pages_volatile) ||
+	    ksm_read_sysfs(KSM_FP("stable_node_chains"), &stable_node_chains) ||
+	    ksm_read_sysfs(KSM_FP("stable_node_dups"), &stable_node_dups) ||
+	    ksm_read_sysfs(KSM_FP("general_profit"), (unsigned long *)&general_profit))
+		return;
+
+	printf("pages_shared      : %lu\n", pages_shared);
+	printf("pages_sharing     : %lu\n", pages_sharing);
+	printf("max_page_sharing  : %lu\n", max_page_sharing);
+	printf("full_scans        : %lu\n", full_scans);
+	printf("pages_unshared    : %lu\n", pages_unshared);
+	printf("pages_volatile    : %lu\n", pages_volatile);
+	printf("stable_node_chains: %lu\n", stable_node_chains);
+	printf("stable_node_dups  : %lu\n", stable_node_dups);
+	printf("general_profit    : %ld\n", general_profit);
+}
+
+static void ksm_print_procfs(void)
+{
+	const char *file_name = "/proc/self/ksm_stat";
+	char buffer[512];
+	FILE *f = fopen(file_name, "r");
+
+	if (!f) {
+		fprintf(stderr, "f %s\n", file_name);
+		perror("fopen");
+		return;
+	}
+
+	while (fgets(buffer, sizeof(buffer), f))
+		printf("%s", buffer);
+
+	fclose(f);
+}
+#endif
+
 static int str_to_prot(char *prot_str)
 {
 	int prot = 0;
@@ -237,6 +286,11 @@ static bool assert_ksm_pages_count(long dupl_page_count)
 	    ksm_read_sysfs(KSM_FP("max_page_sharing"), &max_page_sharing))
 		return false;
 
+#ifdef DEBUG
+	ksm_print_sysfs();
+	ksm_print_procfs();
+#endif
+
 	/*
 	 * Since there must be at least 2 pages for merging and 1 page can be
 	 * shared with the limited number of pages (max_page_sharing), sometimes
-- 
2.30.2

Re: [RFC PATCH v2 00/19] mm: process/cgroup ksm support

[Matthew Wilcox]

On Fri, Feb 10, 2023 at 01:50:04PM -0800, Stefan Roesch wrote:
> So far KSM can only be enabled by calling madvise for memory regions. What is
> required to enable KSM for more workloads is to enable / disable it at the
> process / cgroup level.
> 
> Use case:
> The madvise call is not available in the programming language. An example for
> this are programs with forked workloads using a garbage collected language without
> pointers. In such a language madvise cannot be made available.
> 
> In addition the addresses of objects get moved around as they are garbage
> collected. KSM sharing needs to be enabled "from the outside" for these type of
> workloads.

Don't you have source code to the interpreter for this mysterious
language?  Usually that would be where we put calls to madvise()

Re: [RFC PATCH v2 00/19] mm: process/cgroup ksm support

[Rik van Riel]

[-- Attachment #1: Type: text/plain, Size: 1231 bytes --]

On Fri, 2023-02-10 at 23:23 +0000, Matthew Wilcox wrote:
> On Fri, Feb 10, 2023 at 01:50:04PM -0800, Stefan Roesch wrote:
> > So far KSM can only be enabled by calling madvise for memory
> > regions. What is
> > required to enable KSM for more workloads is to enable / disable it
> > at the
> > process / cgroup level.
> > 
> > Use case:
> > The madvise call is not available in the programming language. An
> > example for
> > this are programs with forked workloads using a garbage collected
> > language without
> > pointers. In such a language madvise cannot be made available.
> > 
> > In addition the addresses of objects get moved around as they are
> > garbage
> > collected. KSM sharing needs to be enabled "from the outside" for
> > these type of
> > workloads.
> 
> Don't you have source code to the interpreter for this mysterious
> language?  Usually that would be where we put calls to madvise()

That same interpreter is also used for workloads where
KSM brings no benefit, and we don't want the overhead
of KSM.

It really would be useful to have the ability to enable
this on a per workload basis, for programming languages
that do not support madvise.

-- 
All Rights Reversed.

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

Re: [RFC PATCH v2 00/19] mm: process/cgroup ksm support

[Johannes Weiner]

Hi Stefan,

On Fri, Feb 10, 2023 at 01:50:04PM -0800, Stefan Roesch wrote:
> So far KSM can only be enabled by calling madvise for memory regions. What is
> required to enable KSM for more workloads is to enable / disable it at the
> process / cgroup level.
> 
> Use case:
> The madvise call is not available in the programming language. An example for
> this are programs with forked workloads using a garbage collected language without
> pointers. In such a language madvise cannot be made available.
> 
> In addition the addresses of objects get moved around as they are garbage
> collected. KSM sharing needs to be enabled "from the outside" for these type of
> workloads.

It would be good to expand on the argument that Rik made about the
interpreter being used for things were there are no merging
opportunities, and the KSM scanning overhead isn't amortized.

There is a fundamental mismatch in scopes. madvise() is a
workload-local decision, whereas sizable sharing opportunities may or
may not exist across multiple workloads. Only a higher-level entity
like a job scheduler can know for certain whether it's running one or
more instances of a job. That job scheduler in turn doesn't have the
necessary knowledge of the workload's internals to make targeted and
well-timed advise calls with, say, process_madvise().

This also applies to the security concerns brought up in previous
threads. An individual workload doesn't know what else is running on
the machine, so it needs to be highly conservative about what it can
give up for system-wide merging. However, if the system is dedicated
to running multiple jobs within the same security domain, it's the job
scheduler that knows that sharing isn't a problem, and even desirable.

So I think this series makes sense, but it would be good to expand a
bit on the reasoning and address the security aspect in the cover/doc.

> Stefan Roesch (19):
>   mm: add new flag to enable ksm per process
>   mm: add flag to __ksm_enter
>   mm: add flag to __ksm_exit call
>   mm: invoke madvise for all vmas in scan_get_next_rmap_item
>   mm: support disabling of ksm for a process
>   mm: add new prctl option to get and set ksm for a process

The implementation looks sound to me as well.

I think it would be a bit easier to review if you folded these ^^^
patches, the tools patch below, and the prctl selftests, all into one
single commit. It's one logical change. This way the new flags and
helper functions can be reviewed against the new users and callsites
without having to jump back and forth between emails.

>   mm: split off pages_volatile function
>   mm: expose general_profit metric
>   docs: document general_profit sysfs knob
>   mm: calculate ksm process profit metric
>   mm: add ksm_merge_type() function
>   mm: expose ksm process profit metric in ksm_stat
>   mm: expose ksm merge type in ksm_stat
>   docs: document new procfs ksm knobs

Same with the new knobs/stats and their documentation.

Logical splitting is easier to follow than geographical splitting.

Thanks!

Re: [RFC PATCH v2 00/19] mm: process/cgroup ksm support

[Stefan Roesch]

Johannes Weiner <hannes@cmpxchg.org> writes:

> Hi Stefan,
>
> On Fri, Feb 10, 2023 at 01:50:04PM -0800, Stefan Roesch wrote:
>> So far KSM can only be enabled by calling madvise for memory regions. What is
>> required to enable KSM for more workloads is to enable / disable it at the
>> process / cgroup level.
>>
>> Use case:
>> The madvise call is not available in the programming language. An example for
>> this are programs with forked workloads using a garbage collected language without
>> pointers. In such a language madvise cannot be made available.
>>
>> In addition the addresses of objects get moved around as they are garbage
>> collected. KSM sharing needs to be enabled "from the outside" for these type of
>> workloads.
>
> It would be good to expand on the argument that Rik made about the
> interpreter being used for things were there are no merging
> opportunities, and the KSM scanning overhead isn't amortized.
>
> There is a fundamental mismatch in scopes. madvise() is a
> workload-local decision, whereas sizable sharing opportunities may or
> may not exist across multiple workloads. Only a higher-level entity
> like a job scheduler can know for certain whether it's running one or
> more instances of a job. That job scheduler in turn doesn't have the
> necessary knowledge of the workload's internals to make targeted and
> well-timed advise calls with, say, process_madvise().
>
> This also applies to the security concerns brought up in previous
> threads. An individual workload doesn't know what else is running on
> the machine, so it needs to be highly conservative about what it can
> give up for system-wide merging. However, if the system is dedicated
> to running multiple jobs within the same security domain, it's the job
> scheduler that knows that sharing isn't a problem, and even desirable.
>
> So I think this series makes sense, but it would be good to expand a
> bit on the reasoning and address the security aspect in the cover/doc.
>

These are good points Johannes, I'll elaborate on them with the next
version of the patch.

>> Stefan Roesch (19):
>>   mm: add new flag to enable ksm per process
>>   mm: add flag to __ksm_enter
>>   mm: add flag to __ksm_exit call
>>   mm: invoke madvise for all vmas in scan_get_next_rmap_item
>>   mm: support disabling of ksm for a process
>>   mm: add new prctl option to get and set ksm for a process
>
> The implementation looks sound to me as well.
>
> I think it would be a bit easier to review if you folded these ^^^
> patches, the tools patch below, and the prctl selftests, all into one
> single commit. It's one logical change. This way the new flags and
> helper functions can be reviewed against the new users and callsites
> without having to jump back and forth between emails.
>

I'll fold them in the next version.

>>   mm: split off pages_volatile function
>>   mm: expose general_profit metric
>>   docs: document general_profit sysfs knob
>>   mm: calculate ksm process profit metric
>>   mm: add ksm_merge_type() function
>>   mm: expose ksm process profit metric in ksm_stat
>>   mm: expose ksm merge type in ksm_stat
>>   docs: document new procfs ksm knobs
>
> Same with the new knobs/stats and their documentation.
>

I'll fold them in the next version.

> Logical splitting is easier to follow than geographical splitting.
>
> Thanks!