[PATCH v9 0/3] mm: process/cgroup ksm support

[PATCH v9 0/3] mm: process/cgroup ksm support

[Stefan Roesch]

So far KSM can only be enabled by calling madvise for memory regions. To
be able to use KSM for more workloads, KSM needs to have the ability to be
enabled / disabled at the process / cgroup level.

Use case 1:
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.

Use case 2:
The same interpreter can also be used for workloads where KSM brings no
benefit or even has overhead. We'd like to be able to enable KSM on a workload
by workload basis.

Use case 3:
With the madvise call sharing opportunities are only enabled for the current
process: it is a workload-local decision. A considerable number of sharing
opportunities may exist across multiple workloads or jobs (if they are part
of the same security domain). Only a higler level entity like a job scheduler
or container can know for certain if its running one or more instances of a
job. That job scheduler however doesn't have the necessary internal workload
knowledge to make targeted madvise calls.

Security concerns:
In previous discussions security concerns have been brought up. The problem is
that an individual workload does not have the knowledge about what else is
running on a machine. Therefore it has to be very conservative in what memory
areas can be shared or not. However, if the system is dedicated to running
multiple jobs within the same security domain, its the job scheduler that has
the knowledge that sharing can be safely enabled and is even desirable.

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

Here are the metrics from an instagram workload (taken from a machine with
64GB main memory):

   full_scans: 445
   general_profit: 20158298048
   max_page_sharing: 256
   merge_across_nodes: 1
   pages_shared: 129547
   pages_sharing: 5119146
   pages_to_scan: 4000
   pages_unshared: 1760924
   pages_volatile: 10761341
   run: 1
   sleep_millisecs: 20
   stable_node_chains: 167
   stable_node_chains_prune_millisecs: 2000
   stable_node_dups: 2751
   use_zero_pages: 0
   zero_pages_sharing: 0

After the service is running for 30 minutes to an hour, 4 to 5 million shared
pages are common for this workload when using KSM.


Detailed changes:

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.

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 metric to /proc/<pid>/ksm_stat.

5. Add more tests to ksm_tests and ksm_functional_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 two new tests to ksm_functional_tests: one to test the new
prctl options and the other one is a fork test to verify that the KSM process
setting is inherited by client processes.


Changes:
- V9:
  - simplify __ksm_add_vma()
  - Adding return to test_prctl() in ksm_functional_tests.c
  - Removing assignment in defining debug variable in ksm_tests.c
  
- V8:
  - Refreshed to latest mm-unstable
  - Added check for arg3 - arg5 in prctl function
  - Don't return an error ksm_enable_merge_any if MMF_VM_MERGE_ANY bit is
    already set

  - unmap after merge in ksm_tests program
  - use tmp variable in main function in ksm_tests program
  
  - Specify all 5 parameters in call to prctl in test programs
  - Rename test_ksm_prctl() to test_prctl()
  - Skip if first test in test_prctl failed with skip result
  - Exit early for failures in test_prctl

  - Rename test_ksm_fork() to test_prctl_fork()
  - Similar changes to test_prctl also for test_prctl_fork()
  - Change number of test
  
- V7:
  - Removed ksm_add_mm() function
  - added ksm_enable_merge_any() function
  - Made ksm_add_vmas() function static
  - Simplified ksm_fork function to only MMF_VM_MERGE_ANY bit
  - Moved setting of bit MMF_VM_MERGE_ANY to ksm_enable_merge_any()
  - Removed flag parameter from __ksm_enter
  - Removed flag parameter from __ksm_exit
  - Clear bit MMF_VM_MERGE_ANY in __ksm_exit
  - call ksm_add_vma only in mmap_region() and do_brk_flags()

  - Removed check_ksm_fork() and check_ksm_merge_type from ksm_tests
  - Removed -F and -G command line options
  - Removed enum options for above tests
  - Added -d option to enable debug mode
  - Added debug variable for storing debug option

- V6:
  - Fix error condition in prctl call
  - Remove ksm_merge_type function and ksm_stat output
  - Some minor changes like whitespace and removing a cast.
  
- V5:
  - When the prctl system call is invoked, mark all compatible VMA
    as mergeable
  - Instead of checcking during scan if VMA is mergeable, mark the VMA
    mergeable when the VMA is created (in case the VMA is compatible)
    - Remove earlier changes, they are no longer necessary
  - Unset the flag MMF_VM_MERGE_ANY in gmap_mark_unmergeable().
  - When unsetting the MMF_VM_MERGE_ANY flag with prctl, only unset the
    flag
  - Remove pages_volatile function (with the simplar general_profit calculation,
    the function is no longer needed)
  - Use simpler formula for calculation of general_profit

- V4:
  - removing check in prctl for MMF_VM_MERGEABLE in PR_SET_MEMORY_MERGE
    handling
  - Checking for VM_MERGEABLE AND MMF_VM_MERGE_ANY to avoid chaning vm_flags
    - This requires also checking that the vma is compatible. The
      compatibility check is provided by a new helper
    - processes which have set MMF_VM_MERGE_ANY, only need to call the
      helper and not madvise.
  - removed unmerge_vmas function, this function is no longer necessary,
    clearing the MMF_VM_MERGE_ANY bit is sufficient

- V3:
  - folded patch 1 - 6
  - folded patch 7 - 14
  - folded patch 15 - 19
  - Expanded on the use cases in the cover letter
  - Added a section on security concerns to the cover letter

- 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 (3):
  mm: add new api to enable ksm per process
  mm: add new KSM process and sysfs knobs
  selftests/mm: add new selftests for KSM

 Documentation/ABI/testing/sysfs-kernel-mm-ksm |   8 +
 Documentation/admin-guide/mm/ksm.rst          |   5 +-
 arch/s390/mm/gmap.c                           |   7 +
 fs/proc/base.c                                |   3 +
 include/linux/ksm.h                           |  25 ++-
 include/linux/sched/coredump.h                |   1 +
 include/uapi/linux/prctl.h                    |   2 +
 kernel/sys.c                                  |  27 +++
 mm/ksm.c                                      | 125 +++++++++++--
 mm/mmap.c                                     |   3 +
 tools/include/uapi/linux/prctl.h              |   2 +
 tools/testing/selftests/mm/Makefile           |   2 +-
 .../selftests/mm/ksm_functional_tests.c       |  91 ++++++++-
 tools/testing/selftests/mm/ksm_tests.c        | 172 ++++++++++++++----
 14 files changed, 414 insertions(+), 59 deletions(-)


base-commit: f80a6c7a37be043f7b074d1e19638675315e3566
-- 
2.31.1

[PATCH v9 1/3] mm: add new api to enable ksm per process

[Stefan Roesch]

So far KSM can only be enabled by calling madvise for memory regions.  To
be able to use KSM for more workloads, KSM needs to have the ability to be
enabled / disabled at the process / cgroup level.

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.

  1) Introduce new MMF_VM_MERGE_ANY flag

     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.

  2) Setting VM_MERGEABLE on VMA creation

     When a VMA is created, if the MMF_VM_MERGE_ANY flag is set, the
     VM_MERGEABLE flag will be set for this VMA.

  3) support disabling of ksm for a process

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

  4) add new prctl option to get and set ksm for a process

     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.

3. Disabling MMF_VM_MERGE_ANY for storage keys in s390

   In the s390 architecture when storage keys are used, the
   MMF_VM_MERGE_ANY will be disabled.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Bagas Sanjaya <bagasdotme@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 arch/s390/mm/gmap.c            |   7 +++
 include/linux/ksm.h            |  21 ++++++-
 include/linux/sched/coredump.h |   1 +
 include/uapi/linux/prctl.h     |   2 +
 kernel/sys.c                   |  27 +++++++++
 mm/ksm.c                       | 104 +++++++++++++++++++++++++++------
 mm/mmap.c                      |   3 +
 7 files changed, 146 insertions(+), 19 deletions(-)

diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index 5a716bdcba05..0949811761e6 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -2591,6 +2591,13 @@ int gmap_mark_unmergeable(void)
 	int ret;
 	VMA_ITERATOR(vmi, mm, 0);
 
+	/*
+	 * 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.
+	 */
+	clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
+
 	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..fa996373653b 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -18,13 +18,26 @@
 #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_add_vma(struct vm_area_struct *vma);
+int ksm_enable_merge_any(struct mm_struct *mm);
+
 int __ksm_enter(struct mm_struct *mm);
 void __ksm_exit(struct mm_struct *mm);
 
 static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
 {
-	if (test_bit(MMF_VM_MERGEABLE, &oldmm->flags))
-		return __ksm_enter(mm);
+	int ret;
+
+	if (test_bit(MMF_VM_MERGEABLE, &oldmm->flags)) {
+		ret = __ksm_enter(mm);
+		if (ret)
+			return ret;
+	}
+
+	if (test_bit(MMF_VM_MERGE_ANY, &oldmm->flags))
+		set_bit(MMF_VM_MERGE_ANY, &mm->flags);
+
 	return 0;
 }
 
@@ -53,6 +66,10 @@ void folio_migrate_ksm(struct folio *newfolio, struct folio *folio);
 
 #else  /* !CONFIG_KSM */
 
+static inline void ksm_add_vma(struct vm_area_struct *vma)
+{
+}
+
 static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
 {
 	return 0;
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 */
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index b99c0be72577..f23d9a16507f 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -292,4 +292,6 @@ struct prctl_mm_map {
 
 #define PR_GET_AUXV			0x41555856
 
+#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 26c1399e0654..72cdb16e2636 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>
@@ -2687,6 +2688,32 @@ 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 (arg3 || arg4 || arg5)
+			return -EINVAL;
+		if (mmap_write_lock_killable(me->mm))
+			return -EINTR;
+
+		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;
+		}
+		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 290a3eb6d8de..f3f76f2ebe89 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -515,6 +515,28 @@ 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)
 {
@@ -1026,6 +1048,7 @@ 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);
@@ -2408,6 +2431,7 @@ 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 {
@@ -2485,6 +2509,66 @@ 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_set(vma, VM_MERGEABLE);
+}
+
+/**
+ * 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);
+}
+
+static void ksm_add_vmas(struct mm_struct *mm)
+{
+	struct vm_area_struct *vma;
+
+	VMA_ITERATOR(vmi, mm, 0);
+	for_each_vma(vmi, vma)
+		__ksm_add_vma(vma);
+}
+
+/**
+ * ksm_enable_merge_any - Add mm to mm ksm list and enable merging on all
+ *                        compatible VMA's
+ *
+ * @mm:  Pointer to mm
+ *
+ * Returns 0 on success, otherwise error code
+ */
+int ksm_enable_merge_any(struct mm_struct *mm)
+{
+	int err;
+
+	if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))
+		return 0;
+
+	if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
+		err = __ksm_enter(mm);
+		if (err)
+			return err;
+	}
+
+	set_bit(MMF_VM_MERGE_ANY, &mm->flags);
+	ksm_add_vmas(mm);
+
+	return 0;
+}
+
 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
 		unsigned long end, int advice, unsigned long *vm_flags)
 {
@@ -2493,25 +2577,10 @@ 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);
@@ -2615,6 +2684,7 @@ void __ksm_exit(struct mm_struct *mm)
 
 	if (easy_to_free) {
 		mm_slot_free(mm_slot_cache, mm_slot);
+		clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
 		clear_bit(MMF_VM_MERGEABLE, &mm->flags);
 		mmdrop(mm);
 	} else if (mm_slot) {
diff --git a/mm/mmap.c b/mm/mmap.c
index 51cd747884e3..10e573535380 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>
@@ -2691,6 +2692,7 @@ 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);
 
@@ -2963,6 +2965,7 @@ 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;
-- 
2.31.1

[PATCH v9 2/3] mm: add new KSM process and sysfs knobs

[Stefan Roesch]

This adds the general_profit KSM sysfs knob and the process profit metric
knobs to ksm_stat.

1) expose general_profit metric

   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.

2) document general_profit sysfs knob

3) calculate ksm process profit metric

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

4) mm: expose ksm process profit metric in ksm_stat

   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.

5) document new procfs ksm knobs

Signed-off-by: Stefan Roesch <shr@devkernel.io>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 Documentation/ABI/testing/sysfs-kernel-mm-ksm |  8 +++++++
 Documentation/admin-guide/mm/ksm.rst          |  5 ++++-
 fs/proc/base.c                                |  3 +++
 include/linux/ksm.h                           |  4 ++++
 mm/ksm.c                                      | 21 +++++++++++++++++++
 5 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-ksm b/Documentation/ABI/testing/sysfs-kernel-mm-ksm
index d244674a9480..6041a025b65a 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:		April 2023
+KernelVersion:  6.4
+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 eed51a910c94..551083a396fb 100644
--- a/Documentation/admin-guide/mm/ksm.rst
+++ b/Documentation/admin-guide/mm/ksm.rst
@@ -157,6 +157,8 @@ 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
@@ -207,7 +209,8 @@ 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
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 5e0e0ccd47aa..96a6a08c8235 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"
@@ -3207,6 +3208,8 @@ static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns,
 	mm = get_task_mm(task);
 	if (mm) {
 		seq_printf(m, "ksm_rmap_items %lu\n", mm->ksm_rmap_items);
+		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);
 	}
 
diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index fa996373653b..590934bdddcf 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -64,6 +64,10 @@ 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 void ksm_add_vma(struct vm_area_struct *vma)
diff --git a/mm/ksm.c b/mm/ksm.c
index f3f76f2ebe89..a959e8925413 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2962,6 +2962,14 @@ static void wait_while_offlining(void)
 }
 #endif /* CONFIG_MEMORY_HOTREMOVE */
 
+#ifdef CONFIG_PROC_FS
+long ksm_process_profit(struct mm_struct *mm)
+{
+	return 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.
@@ -3226,6 +3234,18 @@ static ssize_t pages_volatile_show(struct kobject *kobj,
 }
 KSM_ATTR_RO(pages_volatile);
 
+static ssize_t general_profit_show(struct kobject *kobj,
+				   struct kobj_attribute *attr, char *buf)
+{
+	long general_profit;
+
+	general_profit = ksm_pages_sharing * PAGE_SIZE -
+				ksm_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)
 {
@@ -3290,6 +3310,7 @@ 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,
 };
 
-- 
2.31.1

[PATCH v9 3/3] selftests/mm: add new selftests for KSM

[Stefan Roesch]

This adds three new tests to the selftests for KSM.  These tests use the
new prctl API's to enable and disable KSM.

1) add new prctl flags to prctl header file in tools dir

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

2) add KSM prctl merge test to ksm_tests

   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.

3) add two functions for debugging merge outcome for ksm_tests

   This adds two functions to report the metrics in /proc/self/ksm_stat
   and /sys/kernel/debug/mm/ksm. The debug output is enabled with the
   -d option.

4) add KSM prctl test to ksm_functional_tests

   This adds a test to the ksm_functional_test that verifies that the
   prctl system call to enable / disable KSM works.

5) add KSM fork test to ksm_functional_test

   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>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Bagas Sanjaya <bagasdotme@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 tools/include/uapi/linux/prctl.h              |   2 +
 tools/testing/selftests/mm/Makefile           |   2 +-
 .../selftests/mm/ksm_functional_tests.c       |  91 ++++++++-
 tools/testing/selftests/mm/ksm_tests.c        | 172 ++++++++++++++----
 4 files changed, 228 insertions(+), 39 deletions(-)

diff --git a/tools/include/uapi/linux/prctl.h b/tools/include/uapi/linux/prctl.h
index 1312a137f7fb..759b3f53e53f 100644
--- a/tools/include/uapi/linux/prctl.h
+++ b/tools/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/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index 5a3434419403..65814bdcaa0c 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -29,7 +29,7 @@ MACHINE ?= $(shell echo $(uname_M) | sed -e 's/aarch64.*/arm64/' -e 's/ppc64.*/p
 # LDLIBS.
 MAKEFLAGS += --no-builtin-rules
 
-CFLAGS = -Wall -I $(top_srcdir) $(EXTRA_CFLAGS) $(KHDR_INCLUDES)
+CFLAGS = -Wall -I $(top_srcdir) -I $(top_srcdir)/tools/include/uapi $(EXTRA_CFLAGS) $(KHDR_INCLUDES)
 LDLIBS = -lrt -lpthread
 
 TEST_GEN_PROGS = cow
diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
index d3f26050dfd7..7bc9fc17c9f0 100644
--- a/tools/testing/selftests/mm/ksm_functional_tests.c
+++ b/tools/testing/selftests/mm/ksm_functional_tests.c
@@ -15,8 +15,10 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <sys/mman.h>
+#include <sys/prctl.h>
 #include <sys/syscall.h>
 #include <sys/ioctl.h>
+#include <sys/wait.h>
 #include <linux/userfaultfd.h>
 
 #include "../kselftest.h"
@@ -237,9 +239,93 @@ static void test_unmerge_uffd_wp(void)
 }
 #endif
 
+/* Verify that KSM can be enabled / queried with prctl. */
+static void test_prctl(void)
+{
+	int ret;
+
+	ksft_print_msg("[RUN] %s\n", __func__);
+
+	ret = prctl(PR_SET_MEMORY_MERGE, 1, 0, 0, 0);
+	if (ret < 0 && errno == EINVAL) {
+		ksft_test_result_skip("PR_SET_MEMORY_MERGE not supported\n");
+		return;
+	} else if (ret) {
+		ksft_test_result_fail("PR_SET_MEMORY_MERGE=1 failed\n");
+		return;
+	}
+
+	ret = prctl(PR_GET_MEMORY_MERGE, 0, 0, 0, 0);
+	if (ret < 0) {
+		ksft_test_result_fail("PR_GET_MEMORY_MERGE failed\n");
+		return;
+	} else if (ret != 1) {
+		ksft_test_result_fail("PR_SET_MEMORY_MERGE=1 not effective\n");
+		return;
+	}
+
+	ret = prctl(PR_SET_MEMORY_MERGE, 0, 0, 0, 0);
+	if (ret) {
+		ksft_test_result_fail("PR_SET_MEMORY_MERGE=0 failed\n");
+		return;
+	}
+
+	ret = prctl(PR_GET_MEMORY_MERGE, 0, 0, 0, 0);
+	if (ret < 0) {
+		ksft_test_result_fail("PR_GET_MEMORY_MERGE failed\n");
+		return;
+	} else if (ret != 0) {
+		ksft_test_result_fail("PR_SET_MEMORY_MERGE=0 not effective\n");
+		return;
+	}
+
+	ksft_test_result_pass("Setting/clearing PR_SET_MEMORY_MERGE works\n");
+}
+
+/* Verify that prctl ksm flag is inherited. */
+static void test_prctl_fork(void)
+{
+	int ret, status;
+	pid_t child_pid;
+
+	ksft_print_msg("[RUN] %s\n", __func__);
+
+	ret = prctl(PR_SET_MEMORY_MERGE, 1, 0, 0, 0);
+	if (ret < 0 && errno == EINVAL) {
+		ksft_test_result_skip("PR_SET_MEMORY_MERGE not supported\n");
+		return;
+	} else if (ret) {
+		ksft_test_result_fail("PR_SET_MEMORY_MERGE=1 failed\n");
+		return;
+	}
+
+	child_pid = fork();
+	if (!child_pid) {
+		exit(prctl(PR_GET_MEMORY_MERGE, 0, 0, 0, 0));
+	} else if (child_pid < 0) {
+		ksft_test_result_fail("fork() failed\n");
+		return;
+	}
+
+	if (waitpid(child_pid, &status, 0) < 0) {
+		ksft_test_result_fail("waitpid() failed\n");
+		return;
+	} else if (WEXITSTATUS(status) != 1) {
+		ksft_test_result_fail("unexpected PR_GET_MEMORY_MERGE result in child\n");
+		return;
+	}
+
+	if (prctl(PR_SET_MEMORY_MERGE, 0, 0, 0, 0)) {
+		ksft_test_result_fail("PR_SET_MEMORY_MERGE=0 failed\n");
+		return;
+	}
+
+	ksft_test_result_pass("PR_SET_MEMORY_MERGE value is inherited\n");
+}
+
 int main(int argc, char **argv)
 {
-	unsigned int tests = 2;
+	unsigned int tests = 4;
 	int err;
 
 #ifdef __NR_userfaultfd
@@ -267,6 +353,9 @@ int main(int argc, char **argv)
 	test_unmerge_uffd_wp();
 #endif
 
+	test_prctl();
+	test_prctl_fork();
+
 	err = ksft_get_fail_cnt();
 	if (err)
 		ksft_exit_fail_msg("%d out of %d tests failed\n",
diff --git a/tools/testing/selftests/mm/ksm_tests.c b/tools/testing/selftests/mm/ksm_tests.c
index 74281593a124..435acebdc325 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 {
@@ -33,9 +36,16 @@ 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,
+	CHECK_KSM_GET_MERGE_TYPE,
 	CHECK_KSM_ZERO_PAGE_MERGE,
 	CHECK_KSM_NUMA_MERGE,
 	KSM_MERGE_TIME,
@@ -44,6 +54,8 @@ enum ksm_test_name {
 	KSM_COW_TIME
 };
 
+int debug;
+
 static int ksm_write_sysfs(const char *file_path, unsigned long val)
 {
 	FILE *f = fopen(file_path, "w");
@@ -82,6 +94,53 @@ static int ksm_read_sysfs(const char *file_path, unsigned long *val)
 	return 0;
 }
 
+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);
+}
+
 static int str_to_prot(char *prot_str)
 {
 	int prot = 0;
@@ -128,7 +187,12 @@ static void print_help(void)
 	       "     Default: %d\n", KSM_USE_ZERO_PAGES_DEFAULT);
 	printf(" -m: change merge_across_nodes tunable\n"
 	       "     Default: %d\n", KSM_MERGE_ACROSS_NODES_DEFAULT);
+	printf(" -d: turn debugging output on\n");
 	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 +240,21 @@ 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, 0, 0, 0)) {
+			perror("prctl");
+			return 1;
+		}
 	}
+
 	if (ksm_write_sysfs(KSM_FP("run"), 1))
 		return 1;
 
@@ -211,6 +284,11 @@ static bool assert_ksm_pages_count(long dupl_page_count)
 	    ksm_read_sysfs(KSM_FP("max_page_sharing"), &max_page_sharing))
 		return false;
 
+	if (debug) {
+		ksm_print_sysfs();
+		ksm_print_procfs();
+	}
+
 	/*
 	 * 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
@@ -266,7 +344,8 @@ 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 +360,15 @@ 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_PRCTL)
+			prctl(PR_SET_MEMORY_MERGE, 0, 0, 0, 0);
 		return KSFT_PASS;
 	}
 
@@ -297,7 +378,7 @@ 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 +394,7 @@ 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 +418,8 @@ 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 +437,7 @@ 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 +483,8 @@ 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 +520,8 @@ 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 +547,8 @@ 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 +590,7 @@ 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 +615,7 @@ 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 +631,7 @@ 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 +656,7 @@ 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 +671,7 @@ 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 +703,7 @@ 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 +742,7 @@ 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 +779,7 @@ 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 +788,7 @@ 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, "dha:p:l:z:m:s:t:MUZNPCHD")) != -1) {
 		switch (opt) {
 		case 'a':
 			prot = str_to_prot(optarg);
@@ -739,12 +822,26 @@ int main(int argc, char *argv[])
 			else
 				merge_across_nodes = 1;
 			break;
+		case 'd':
+			debug = 1;
+			break;
 		case 's':
 			size_MB = atoi(optarg);
 			if (size_MB <= 0) {
 				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 = tmp;
+			}
+			break;
 		case 'M':
 			break;
 		case 'U':
@@ -795,35 +892,36 @@ 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 +929,12 @@ 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;
 	}
 
-- 
2.31.1

[PATCH v1 0/3] mm/ksm: improve PR_SET_MEMORY_MERGE=0 handling and cleanup disabling KSM

[David Hildenbrand]

This is a follow-up to [1]:
	[PATCH v9 0/3] mm: process/cgroup ksm support

which is not in mm-unstable yet (but soon? :) ). I'll be on vacation for
~2 weeks, so sending it out now as reply to [1].

(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.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Stefan Roesch <shr@devkernel.io>
Cc: Rik van Riel <riel@surriel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Shuah Khan <shuah@kernel.org>

[1] https://lkml.kernel.org/r/20230418051342.1919757-1-shr@devkernel.io

David Hildenbrand (3):
  mm/ksm: unmerge and clear VM_MERGEABLE when setting
    PR_SET_MEMORY_MERGE=0
  selftests/ksm: ksm_functional_tests: add prctl unmerge test
  mm/ksm: move disabling KSM from s390/gmap code to KSM code

 arch/s390/mm/gmap.c                           | 20 +------
 include/linux/ksm.h                           |  7 +++
 kernel/sys.c                                  |  7 +--
 mm/ksm.c                                      | 58 +++++++++++++++++++
 .../selftests/mm/ksm_functional_tests.c       | 46 +++++++++++++--
 5 files changed, 107 insertions(+), 31 deletions(-)

-- 
2.39.2

[PATCH v1 1/3] mm/ksm: unmerge and clear VM_MERGEABLE when setting PR_SET_MEMORY_MERGE=0

[David Hildenbrand]

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.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 include/linux/ksm.h |  1 +
 kernel/sys.c        |  7 +------
 mm/ksm.c            | 47 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 49 insertions(+), 6 deletions(-)

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 590934bdddcf..7108bc65dc2a 100644
--- 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 72cdb16e2636..3436376667d7 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2698,12 +2698,7 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 		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;
+			error = ksm_disable_merge_any(me->mm);
 		}
 		mmap_write_unlock(me->mm);
 		break;
diff --git a/mm/ksm.c b/mm/ksm.c
index a959e8925413..813f7fbc1832 100644
--- 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 +2599,23 @@ int ksm_enable_merge_any(struct mm_struct *mm)
 	return 0;
 }
 
+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)
 {
-- 
2.39.2

[PATCH v1 2/3] selftests/ksm: ksm_functional_tests: add prctl unmerge test

[David Hildenbrand]

Let's test whether setting PR_SET_MEMORY_MERGE to 0 after setting it to
1 will unmerge pages, similar to how setting MADV_UNMERGEABLE after setting
MADV_MERGEABLE would.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 .../selftests/mm/ksm_functional_tests.c       | 46 ++++++++++++++++---
 1 file changed, 40 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
index 7bc9fc17c9f0..26853badae70 100644
--- a/tools/testing/selftests/mm/ksm_functional_tests.c
+++ b/tools/testing/selftests/mm/ksm_functional_tests.c
@@ -91,9 +91,10 @@ static int ksm_merge(void)
 	return 0;
 }
 
-static char *mmap_and_merge_range(char val, unsigned long size)
+static char *mmap_and_merge_range(char val, unsigned long size, bool use_prctl)
 {
 	char *map;
+	int ret;
 
 	map = mmap(NULL, size, PROT_READ|PROT_WRITE,
 		   MAP_PRIVATE|MAP_ANON, -1, 0);
@@ -110,7 +111,17 @@ static char *mmap_and_merge_range(char val, unsigned long size)
 
 	/* Make sure each page contains the same values to merge them. */
 	memset(map, val, size);
-	if (madvise(map, size, MADV_MERGEABLE)) {
+
+	if (use_prctl) {
+		ret = prctl(PR_SET_MEMORY_MERGE, 1, 0, 0, 0);
+		if (ret < 0 && errno == EINVAL) {
+			ksft_test_result_skip("PR_SET_MEMORY_MERGE not supported\n");
+			goto unmap;
+		} else if (ret) {
+			ksft_test_result_fail("PR_SET_MEMORY_MERGE=1 failed\n");
+			goto unmap;
+		}
+	} else if (madvise(map, size, MADV_MERGEABLE)) {
 		ksft_test_result_fail("MADV_MERGEABLE failed\n");
 		goto unmap;
 	}
@@ -133,7 +144,7 @@ static void test_unmerge(void)
 
 	ksft_print_msg("[RUN] %s\n", __func__);
 
-	map = mmap_and_merge_range(0xcf, size);
+	map = mmap_and_merge_range(0xcf, size, false);
 	if (map == MAP_FAILED)
 		return;
 
@@ -155,7 +166,7 @@ static void test_unmerge_discarded(void)
 
 	ksft_print_msg("[RUN] %s\n", __func__);
 
-	map = mmap_and_merge_range(0xcf, size);
+	map = mmap_and_merge_range(0xcf, size, false);
 	if (map == MAP_FAILED)
 		return;
 
@@ -187,7 +198,7 @@ static void test_unmerge_uffd_wp(void)
 
 	ksft_print_msg("[RUN] %s\n", __func__);
 
-	map = mmap_and_merge_range(0xcf, size);
+	map = mmap_and_merge_range(0xcf, size, false);
 	if (map == MAP_FAILED)
 		return;
 
@@ -323,9 +334,31 @@ static void test_prctl_fork(void)
 	ksft_test_result_pass("PR_SET_MEMORY_MERGE value is inherited\n");
 }
 
+static void test_prctl_unmerge(void)
+{
+	const unsigned int size = 2 * MiB;
+	char *map;
+
+	ksft_print_msg("[RUN] %s\n", __func__);
+
+	map = mmap_and_merge_range(0xcf, size, true);
+	if (map == MAP_FAILED)
+		return;
+
+	if (prctl(PR_SET_MEMORY_MERGE, 0, 0, 0, 0)) {
+		ksft_test_result_fail("PR_SET_MEMORY_MERGE=0 failed\n");
+		goto unmap;
+	}
+
+	ksft_test_result(!range_maps_duplicates(map, size),
+			 "Pages were unmerged\n");
+unmap:
+	munmap(map, size);
+}
+
 int main(int argc, char **argv)
 {
-	unsigned int tests = 4;
+	unsigned int tests = 5;
 	int err;
 
 #ifdef __NR_userfaultfd
@@ -355,6 +388,7 @@ int main(int argc, char **argv)
 
 	test_prctl();
 	test_prctl_fork();
+	test_prctl_unmerge();
 
 	err = ksft_get_fail_cnt();
 	if (err)
-- 
2.39.2

[PATCH v1 3/3] mm/ksm: move disabling KSM from s390/gmap code to KSM code

[David Hildenbrand]

Let's factor out actual disabling of KSM. The existing
"mm->def_flags &= ~VM_MERGEABLE;" was essentially a NOP and can be dropped,
because def_flags should never include VM_MERGEABLE. Note that we don't
currently prevent re-enabling KSM.

This should now be faster in case KSM was never enabled, because we only
conditionally iterate all VMAs. Further, it certainly looks cleaner.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 arch/s390/mm/gmap.c | 20 +-------------------
 include/linux/ksm.h |  6 ++++++
 mm/ksm.c            | 11 +++++++++++
 3 files changed, 18 insertions(+), 19 deletions(-)

diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index 0949811761e6..dfe905c7bd8e 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -2585,30 +2585,12 @@ EXPORT_SYMBOL_GPL(s390_enable_sie);
 
 int gmap_mark_unmergeable(void)
 {
-	struct mm_struct *mm = current->mm;
-	struct vm_area_struct *vma;
-	unsigned long vm_flags;
-	int ret;
-	VMA_ITERATOR(vmi, mm, 0);
-
 	/*
 	 * 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.
 	 */
-	clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
-
-	for_each_vma(vmi, vma) {
-		/* Copy vm_flags to avoid partial modifications in ksm_madvise */
-		vm_flags = vma->vm_flags;
-		ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
-				  MADV_UNMERGEABLE, &vm_flags);
-		if (ret)
-			return ret;
-		vm_flags_reset(vma, vm_flags);
-	}
-	mm->def_flags &= ~VM_MERGEABLE;
-	return 0;
+	return ksm_disable(current->mm);
 }
 EXPORT_SYMBOL_GPL(gmap_mark_unmergeable);
 
diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 7108bc65dc2a..b3d8b7849e18 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -22,6 +22,7 @@ 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_disable(struct mm_struct *mm);
 
 int __ksm_enter(struct mm_struct *mm);
 void __ksm_exit(struct mm_struct *mm);
@@ -75,6 +76,11 @@ static inline void ksm_add_vma(struct vm_area_struct *vma)
 {
 }
 
+static inline int ksm_disable(struct mm_struct *mm)
+{
+	return 0;
+}
+
 static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
 {
 	return 0;
diff --git a/mm/ksm.c b/mm/ksm.c
index 813f7fbc1832..208311cbb019 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2616,6 +2616,17 @@ int ksm_disable_merge_any(struct mm_struct *mm)
 	return 0;
 }
 
+int ksm_disable(struct mm_struct *mm)
+{
+	mmap_assert_write_locked(mm);
+
+	if (!test_bit(MMF_VM_MERGEABLE, &mm->flags))
+		return 0;
+	if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))
+		return ksm_disable_merge_any(mm);
+	return ksm_del_vmas(mm);
+}
+
 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
 		unsigned long end, int advice, unsigned long *vm_flags)
 {
-- 
2.39.2

Re: [PATCH v1 3/3] mm/ksm: move disabling KSM from s390/gmap code to KSM code

[Janosch Frank]

On 4/18/23 17:28, David Hildenbrand wrote:
> Let's factor out actual disabling of KSM. The existing
> "mm->def_flags &= ~VM_MERGEABLE;" was essentially a NOP and can be dropped,
> because def_flags should never include VM_MERGEABLE. Note that we don't
> currently prevent re-enabling KSM.
> 
> This should now be faster in case KSM was never enabled, because we only
> conditionally iterate all VMAs. Further, it certainly looks cleaner.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>   arch/s390/mm/gmap.c | 20 +-------------------
>   include/linux/ksm.h |  6 ++++++
>   mm/ksm.c            | 11 +++++++++++
>   3 files changed, 18 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> index 0949811761e6..dfe905c7bd8e 100644
> --- a/arch/s390/mm/gmap.c
> +++ b/arch/s390/mm/gmap.c
> @@ -2585,30 +2585,12 @@ EXPORT_SYMBOL_GPL(s390_enable_sie);
>   
>   int gmap_mark_unmergeable(void)
>   {
> -	struct mm_struct *mm = current->mm;
> -	struct vm_area_struct *vma;
> -	unsigned long vm_flags;
> -	int ret;
> -	VMA_ITERATOR(vmi, mm, 0);
> -
>   	/*
>   	 * 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.
>   	 */

Is that still true?

My KSM knowledge is nearly zero but from what I can see the patch looks 
ok to me:
Acked-by: Janosch Frank <frankja@linux.ibm.net>

Re: [PATCH v1 3/3] mm/ksm: move disabling KSM from s390/gmap code to KSM code

[David Hildenbrand]

On 19.04.23 13:39, Janosch Frank wrote:
> On 4/18/23 17:28, David Hildenbrand wrote:
>> Let's factor out actual disabling of KSM. The existing
>> "mm->def_flags &= ~VM_MERGEABLE;" was essentially a NOP and can be dropped,
>> because def_flags should never include VM_MERGEABLE. Note that we don't
>> currently prevent re-enabling KSM.
>>
>> This should now be faster in case KSM was never enabled, because we only
>> conditionally iterate all VMAs. Further, it certainly looks cleaner.
>>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>>    arch/s390/mm/gmap.c | 20 +-------------------
>>    include/linux/ksm.h |  6 ++++++
>>    mm/ksm.c            | 11 +++++++++++
>>    3 files changed, 18 insertions(+), 19 deletions(-)
>>
>> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
>> index 0949811761e6..dfe905c7bd8e 100644
>> --- a/arch/s390/mm/gmap.c
>> +++ b/arch/s390/mm/gmap.c
>> @@ -2585,30 +2585,12 @@ EXPORT_SYMBOL_GPL(s390_enable_sie);
>>    
>>    int gmap_mark_unmergeable(void)
>>    {
>> -	struct mm_struct *mm = current->mm;
>> -	struct vm_area_struct *vma;
>> -	unsigned long vm_flags;
>> -	int ret;
>> -	VMA_ITERATOR(vmi, mm, 0);
>> -
>>    	/*
>>    	 * 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.
>>    	 */
> 
> Is that still true?

Yes. We'd need another per-MM bit to stop it from getting re-enabled.

> 
> My KSM knowledge is nearly zero but from what I can see the patch looks
> ok to me:
> Acked-by: Janosch Frank <frankja@linux.ibm.net>


Thanks!

-- 
Thanks,

David / dhildenb

Re: [PATCH v1 1/3] mm/ksm: unmerge and clear VM_MERGEABLE when setting PR_SET_MEMORY_MERGE=0

[Stefan Roesch]

David Hildenbrand <david@redhat.com> writes:

> 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.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  include/linux/ksm.h |  1 +
>  kernel/sys.c        |  7 +------
>  mm/ksm.c            | 47 +++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 49 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/ksm.h b/include/linux/ksm.h
> index 590934bdddcf..7108bc65dc2a 100644
> --- 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 72cdb16e2636..3436376667d7 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -2698,12 +2698,7 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>  		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;
> +			error = ksm_disable_merge_any(me->mm);
>  		}
>
nit:
can we do:

    if (arg2)
   	error = ksm_enable_merge_any(me->mm);
	else
   	error = ksm_disable_merge_any(me->mm);
	mmap_write_unlock(me->mm);
	break;

> diff --git a/mm/ksm.c b/mm/ksm.c
> index a959e8925413..813f7fbc1832 100644
> --- 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 +2599,23 @@ int ksm_enable_merge_any(struct mm_struct *mm)
>  	return 0;
>  }
>
> +int ksm_disable_merge_any(struct mm_struct *mm)
>

I understand we want to keep the name "symmetric" with
ksm_enable_merge_any, but it also unmerges the ksm pages. Do we want to
reflect that in the function name?

Can we add a comment for the function?

> +{
> +	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);
>

We only clear the MMF_VM_MERGE_ANY flag if there are no errors. Is this
what we want? This means that if the process creates new memory regions
they would still be marked as mergeable.

> +	return 0;
> +}
> +
>  int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
>  		unsigned long end, int advice, unsigned long *vm_flags)
>  {

Re: [PATCH v1 2/3] selftests/ksm: ksm_functional_tests: add prctl unmerge test

[Stefan Roesch]

David Hildenbrand <david@redhat.com> writes:

> Let's test whether setting PR_SET_MEMORY_MERGE to 0 after setting it to
> 1 will unmerge pages, similar to how setting MADV_UNMERGEABLE after setting
> MADV_MERGEABLE would.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  .../selftests/mm/ksm_functional_tests.c       | 46 ++++++++++++++++---
>  1 file changed, 40 insertions(+), 6 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
> index 7bc9fc17c9f0..26853badae70 100644
> --- a/tools/testing/selftests/mm/ksm_functional_tests.c
> +++ b/tools/testing/selftests/mm/ksm_functional_tests.c
> @@ -91,9 +91,10 @@ static int ksm_merge(void)
>  	return 0;
>  }
>
> -static char *mmap_and_merge_range(char val, unsigned long size)
> +static char *mmap_and_merge_range(char val, unsigned long size, bool use_prctl)
>  {
>  	char *map;
> +	int ret;
>
>  	map = mmap(NULL, size, PROT_READ|PROT_WRITE,
>  		   MAP_PRIVATE|MAP_ANON, -1, 0);
> @@ -110,7 +111,17 @@ static char *mmap_and_merge_range(char val, unsigned long size)
>
>  	/* Make sure each page contains the same values to merge them. */
>  	memset(map, val, size);
> -	if (madvise(map, size, MADV_MERGEABLE)) {
> +
> +	if (use_prctl) {
> +		ret = prctl(PR_SET_MEMORY_MERGE, 1, 0, 0, 0);
> +		if (ret < 0 && errno == EINVAL) {
> +			ksft_test_result_skip("PR_SET_MEMORY_MERGE not supported\n");
> +			goto unmap;
> +		} else if (ret) {
> +			ksft_test_result_fail("PR_SET_MEMORY_MERGE=1 failed\n");
> +			goto unmap;
> +		}
> +	} else if (madvise(map, size, MADV_MERGEABLE)) {
>  		ksft_test_result_fail("MADV_MERGEABLE failed\n");
>  		goto unmap;
>  	}
> @@ -133,7 +144,7 @@ static void test_unmerge(void)
>
>  	ksft_print_msg("[RUN] %s\n", __func__);
>
> -	map = mmap_and_merge_range(0xcf, size);
> +	map = mmap_and_merge_range(0xcf, size, false);
>  	if (map == MAP_FAILED)
>  		return;
>
> @@ -155,7 +166,7 @@ static void test_unmerge_discarded(void)
>
>  	ksft_print_msg("[RUN] %s\n", __func__);
>
> -	map = mmap_and_merge_range(0xcf, size);
> +	map = mmap_and_merge_range(0xcf, size, false);
>  	if (map == MAP_FAILED)
>  		return;
>
> @@ -187,7 +198,7 @@ static void test_unmerge_uffd_wp(void)
>
>  	ksft_print_msg("[RUN] %s\n", __func__);
>
> -	map = mmap_and_merge_range(0xcf, size);
> +	map = mmap_and_merge_range(0xcf, size, false);
>  	if (map == MAP_FAILED)
>  		return;
>
> @@ -323,9 +334,31 @@ static void test_prctl_fork(void)
>  	ksft_test_result_pass("PR_SET_MEMORY_MERGE value is inherited\n");
>  }
>
> +static void test_prctl_unmerge(void)
> +{
> +	const unsigned int size = 2 * MiB;
> +	char *map;
> +
> +	ksft_print_msg("[RUN] %s\n", __func__);
> +
> +	map = mmap_and_merge_range(0xcf, size, true);
> +	if (map == MAP_FAILED)
> +		return;
> +
> +	if (prctl(PR_SET_MEMORY_MERGE, 0, 0, 0, 0)) {
> +		ksft_test_result_fail("PR_SET_MEMORY_MERGE=0 failed\n");
> +		goto unmap;
> +	}
> +
> +	ksft_test_result(!range_maps_duplicates(map, size),
> +			 "Pages were unmerged\n");
> +unmap:
> +	munmap(map, size);
> +}
> +
>  int main(int argc, char **argv)
>  {
> -	unsigned int tests = 4;
> +	unsigned int tests = 5;
>  	int err;
>
>  #ifdef __NR_userfaultfd
> @@ -355,6 +388,7 @@ int main(int argc, char **argv)
>
>  	test_prctl();
>  	test_prctl_fork();
> +	test_prctl_unmerge();
>
>  	err = ksft_get_fail_cnt();
>  	if (err)

Acked-by: Stefan Roesch <shr@devkernel.io>

Re: [PATCH v1 3/3] mm/ksm: move disabling KSM from s390/gmap code to KSM code

[Stefan Roesch]

David Hildenbrand <david@redhat.com> writes:

> Let's factor out actual disabling of KSM. The existing
> "mm->def_flags &= ~VM_MERGEABLE;" was essentially a NOP and can be dropped,
> because def_flags should never include VM_MERGEABLE. Note that we don't
> currently prevent re-enabling KSM.
>
> This should now be faster in case KSM was never enabled, because we only
> conditionally iterate all VMAs. Further, it certainly looks cleaner.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  arch/s390/mm/gmap.c | 20 +-------------------
>  include/linux/ksm.h |  6 ++++++
>  mm/ksm.c            | 11 +++++++++++
>  3 files changed, 18 insertions(+), 19 deletions(-)
>
> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> index 0949811761e6..dfe905c7bd8e 100644
> --- a/arch/s390/mm/gmap.c
> +++ b/arch/s390/mm/gmap.c
> @@ -2585,30 +2585,12 @@ EXPORT_SYMBOL_GPL(s390_enable_sie);
>
>  int gmap_mark_unmergeable(void)
>  {
> -	struct mm_struct *mm = current->mm;
> -	struct vm_area_struct *vma;
> -	unsigned long vm_flags;
> -	int ret;
> -	VMA_ITERATOR(vmi, mm, 0);
> -
>  	/*
>  	 * 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.
>  	 */
> -	clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
> -
> -	for_each_vma(vmi, vma) {
> -		/* Copy vm_flags to avoid partial modifications in ksm_madvise */
> -		vm_flags = vma->vm_flags;
> -		ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
> -				  MADV_UNMERGEABLE, &vm_flags);
> -		if (ret)
> -			return ret;
> -		vm_flags_reset(vma, vm_flags);
> -	}
> -	mm->def_flags &= ~VM_MERGEABLE;
>

This clears the def_flags struct member, however, in ksm_disable() we
clear the __flags struct member. Is this a problem?

> -	return 0;
> +	return ksm_disable(current->mm);
>  }
>  EXPORT_SYMBOL_GPL(gmap_mark_unmergeable);
>
> diff --git a/include/linux/ksm.h b/include/linux/ksm.h
> index 7108bc65dc2a..b3d8b7849e18 100644
> --- a/include/linux/ksm.h
> +++ b/include/linux/ksm.h
> @@ -22,6 +22,7 @@ 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_disable(struct mm_struct *mm);
>
>  int __ksm_enter(struct mm_struct *mm);
>  void __ksm_exit(struct mm_struct *mm);
> @@ -75,6 +76,11 @@ static inline void ksm_add_vma(struct vm_area_struct *vma)
>  {
>  }
>
> +static inline int ksm_disable(struct mm_struct *mm)
> +{
> +	return 0;
> +}
> +
>  static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
>  {
>  	return 0;
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 813f7fbc1832..208311cbb019 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -2616,6 +2616,17 @@ int ksm_disable_merge_any(struct mm_struct *mm)
>  	return 0;
>  }
>
> +int ksm_disable(struct mm_struct *mm)
> +{
> +	mmap_assert_write_locked(mm);
> +
> +	if (!test_bit(MMF_VM_MERGEABLE, &mm->flags))
> +		return 0;
> +	if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))
> +		return ksm_disable_merge_any(mm);
> +	return ksm_del_vmas(mm);
> +}
> +
>  int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
>  		unsigned long end, int advice, unsigned long *vm_flags)
>  {

Re: [PATCH v1 3/3] mm/ksm: move disabling KSM from s390/gmap code to KSM code

[David Hildenbrand]

[...]

>> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
>> index 0949811761e6..dfe905c7bd8e 100644
>> --- a/arch/s390/mm/gmap.c
>> +++ b/arch/s390/mm/gmap.c
>> @@ -2585,30 +2585,12 @@ EXPORT_SYMBOL_GPL(s390_enable_sie);
>>
>>   int gmap_mark_unmergeable(void)
>>   {
>> -	struct mm_struct *mm = current->mm;
>> -	struct vm_area_struct *vma;
>> -	unsigned long vm_flags;
>> -	int ret;
>> -	VMA_ITERATOR(vmi, mm, 0);
>> -
>>   	/*
>>   	 * 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.
>>   	 */
>> -	clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
>> -
>> -	for_each_vma(vmi, vma) {
>> -		/* Copy vm_flags to avoid partial modifications in ksm_madvise */
>> -		vm_flags = vma->vm_flags;
>> -		ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
>> -				  MADV_UNMERGEABLE, &vm_flags);
>> -		if (ret)
>> -			return ret;
>> -		vm_flags_reset(vma, vm_flags);
>> -	}
>> -	mm->def_flags &= ~VM_MERGEABLE;
>>
> 

Hi Stefan,

> This clears the def_flags struct member, however, in ksm_disable() we
> clear the __flags struct member. Is this a problem?

The patch description contains a comment regarding def_flags: "The 
existing "mm->def_flags &= ~VM_MERGEABLE;" was essentially a NOP and can 
be dropped, because def_flags should never include VM_MERGEABLE."

We keep clearing the MADV_UNMERGEABLE flag from MADV_UNMERGEABLE. In the 
old code, ksm_madvise() would have cleared it from local vm_flags and 
vm_flags_reset() would have modified vma->vm_flags. Now we clear it 
directly via vm_flags_clear(vma, VM_MERGEABLE);


Long story short, the mm->def_flags code as wrong and most probably 
copied from thp_split_mm() where we do:
	mm->def_flags |= VM_NOHUGEPAGE;
Which makes more sense.

Thanks!

-- 
Thanks,

David / dhildenb

Re: [PATCH v1 1/3] mm/ksm: unmerge and clear VM_MERGEABLE when setting PR_SET_MEMORY_MERGE=0

[David Hildenbrand]

[...]

>>
> nit:
> can we do:
> 
>      if (arg2)
>     	error = ksm_enable_merge_any(me->mm);
> 	else
>     	error = ksm_disable_merge_any(me->mm);
> 	mmap_write_unlock(me->mm);
> 	break;

Indeed, thanks.

> 
>> diff --git a/mm/ksm.c b/mm/ksm.c
>> index a959e8925413..813f7fbc1832 100644
>> --- 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 +2599,23 @@ int ksm_enable_merge_any(struct mm_struct *mm)
>>   	return 0;
>>   }
>>
>> +int ksm_disable_merge_any(struct mm_struct *mm)
>>
> 
> I understand we want to keep the name "symmetric" with
> ksm_enable_merge_any, but it also unmerges the ksm pages. Do we want to
> reflect that in the function name?

ksm_disable_merge_any_umerge() is suboptimal.

As ksm_disable_merge_any() now reverts what ksm_enable_merge_any() ended 
up doing, I think it's just fine.

(it would be a different story if we'd be using "set" / "clear" 
terminology instead of "enable" / "disable").

We can describe that in the comment.

> 
> Can we add a comment for the function?

Can do for symmetry with ksm_enable_merge_any().

But note that I don't think documentation for functions is of any help 
when it takes longer to read the documentation than to read+understand 
the actual code.

> 
>> +{
>> +	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);
>>
> 
> We only clear the MMF_VM_MERGE_ANY flag if there are no errors. Is this

I think this is the behavior we want. We tried to disable KSM for the 
process (previously enabled via the prctl), but cannot disable KSM. So 
we rollback our changes and return an error.

This is similar to trying to set MADV_UNMERGEABLE but failing. We leave 
the bit set.

> what we want? This means that if the process creates new memory regions
> they would still be marked as mergeable.

Yes, we failed the operation so we keep everything unchanged.

-- 
Thanks,

David / dhildenb

Re: [PATCH v1 1/3] mm/ksm: unmerge and clear VM_MERGEABLE when setting PR_SET_MEMORY_MERGE=0

[David Hildenbrand]

>> I understand we want to keep the name "symmetric" with
>> ksm_enable_merge_any, but it also unmerges the ksm pages. Do we want to
>> reflect that in the function name?
> 
> ksm_disable_merge_any_umerge() is suboptimal.
> 
> As ksm_disable_merge_any() now reverts what ksm_enable_merge_any() ended
> up doing, I think it's just fine.
> 
> (it would be a different story if we'd be using "set" / "clear"
> terminology instead of "enable" / "disable").
> 
> We can describe that in the comment.
> 
>>
>> Can we add a comment for the function?
> 
> Can do for symmetry with ksm_enable_merge_any().
> 

+/**
+ * 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
+ */


-- 
Thanks,

David / dhildenb

Re: [PATCH v1 3/3] mm/ksm: move disabling KSM from s390/gmap code to KSM code

[Stefan Roesch]

David Hildenbrand <david@redhat.com> writes:

> [...]
>
>>> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
>>> index 0949811761e6..dfe905c7bd8e 100644
>>> --- a/arch/s390/mm/gmap.c
>>> +++ b/arch/s390/mm/gmap.c
>>> @@ -2585,30 +2585,12 @@ EXPORT_SYMBOL_GPL(s390_enable_sie);
>>>
>>>   int gmap_mark_unmergeable(void)
>>>   {
>>> -	struct mm_struct *mm = current->mm;
>>> -	struct vm_area_struct *vma;
>>> -	unsigned long vm_flags;
>>> -	int ret;
>>> -	VMA_ITERATOR(vmi, mm, 0);
>>> -
>>>   	/*
>>>   	 * 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.
>>>   	 */
>>> -	clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
>>> -
>>> -	for_each_vma(vmi, vma) {
>>> -		/* Copy vm_flags to avoid partial modifications in ksm_madvise */
>>> -		vm_flags = vma->vm_flags;
>>> -		ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
>>> -				  MADV_UNMERGEABLE, &vm_flags);
>>> -		if (ret)
>>> -			return ret;
>>> -		vm_flags_reset(vma, vm_flags);
>>> -	}
>>> -	mm->def_flags &= ~VM_MERGEABLE;
>>>
>>
>
> Hi Stefan,
>
>> This clears the def_flags struct member, however, in ksm_disable() we
>> clear the __flags struct member. Is this a problem?
>
> The patch description contains a comment regarding def_flags: "The existing
> "mm->def_flags &= ~VM_MERGEABLE;" was essentially a NOP and can be dropped,
> because def_flags should never include VM_MERGEABLE."
>
> We keep clearing the MADV_UNMERGEABLE flag from MADV_UNMERGEABLE. In the old
> code, ksm_madvise() would have cleared it from local vm_flags and
> vm_flags_reset() would have modified vma->vm_flags. Now we clear it directly via
> vm_flags_clear(vma, VM_MERGEABLE);
>
>
> Long story short, the mm->def_flags code as wrong and most probably copied from
> thp_split_mm() where we do:
> 	mm->def_flags |= VM_NOHUGEPAGE;
> Which makes more sense.
>
> Thanks!

Thanks for the explanation.

Acked-by: Stefan Roesch <shr@devkernel.io>

Re: [PATCH v1 1/3] mm/ksm: unmerge and clear VM_MERGEABLE when setting PR_SET_MEMORY_MERGE=0

[Stefan Roesch]

David Hildenbrand <david@redhat.com> writes:

>>> I understand we want to keep the name "symmetric" with
>>> ksm_enable_merge_any, but it also unmerges the ksm pages. Do we want to
>>> reflect that in the function name?
>> ksm_disable_merge_any_umerge() is suboptimal.
>> As ksm_disable_merge_any() now reverts what ksm_enable_merge_any() ended
>> up doing, I think it's just fine.
>> (it would be a different story if we'd be using "set" / "clear"
>> terminology instead of "enable" / "disable").
>> We can describe that in the comment.
>>
>>>
>>> Can we add a comment for the function?
>> Can do for symmetry with ksm_enable_merge_any().
>>
>
> +/**
> + * 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
> + */


LGTM

Acked-by: Stefan Roesch <shr@devkernel.io>

[PATCH v9 2/3] mm: add new KSM process and sysfs knobs

[xu xin]

> This adds the general_profit KSM sysfs knob and the process profit metric
> knobs to ksm_stat.
> 
> 1) expose general_profit metric
> 
>    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.
> 
> 2) document general_profit sysfs knob
> 
> 3) calculate ksm process profit metric
> 
>    The ksm documentation mentions the process profit metric and how to
>    calculate it.  This adds the calculation of the metric.
> 
> 4) mm: expose ksm process profit metric in ksm_stat
> 
>    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.
>

Hi, Stefan, I think you should give some credits to me about my contributions on
the concept and formula of ksm profit (process wide and system wide),  it's kind
of idea stealing.


Besides, the idea of Process control KSM was proposed by me last year although you use
prctl instead of /proc fs. you even didn't CC my email. I think you should CC my email
(xu.xin16@zte.com.cn) as least.
 
> 5) document new procfs ksm knobs
> 
> Signed-off-by: Stefan Roesch <shr@devkernel.io>
> Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Rik van Riel <riel@surriel.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>  Documentation/ABI/testing/sysfs-kernel-mm-ksm |  8 +++++++
>  Documentation/admin-guide/mm/ksm.rst          |  5 ++++-
>  fs/proc/base.c                                |  3 +++
>  include/linux/ksm.h                           |  4 ++++
>  mm/ksm.c                                      | 21 +++++++++++++++++++
>  5 files changed, 40 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-ksm b/Documentation/ABI/testing/sysfs-kernel-mm-ksm
> index d244674a9480..6041a025b65a 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:		April 2023
> +KernelVersion:  6.4
> +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

Re: [PATCH v9 2/3] mm: add new KSM process and sysfs knobs

[Stefan Roesch]

xu xin <xu.xin.sc@gmail.com> writes:

>> This adds the general_profit KSM sysfs knob and the process profit metric
>> knobs to ksm_stat.
>>
>> 1) expose general_profit metric
>>
>>    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.
>>
>> 2) document general_profit sysfs knob
>>
>> 3) calculate ksm process profit metric
>>
>>    The ksm documentation mentions the process profit metric and how to
>>    calculate it.  This adds the calculation of the metric.
>>
>> 4) mm: expose ksm process profit metric in ksm_stat
>>
>>    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.
>>
>
> Hi, Stefan, I think you should give some credits to me about my contributions on
> the concept and formula of ksm profit (process wide and system wide),  it's kind
> of idea stealing.
>
>

I wasn't aware the formula that is described in the documentation is
from you. I simply implemented the documented metrics. If you came up
with it, happy to give you credit.

> Besides, the idea of Process control KSM was proposed by me last year although you use
> prctl instead of /proc fs. you even didn't CC my email. I think you should CC my email
> (xu.xin16@zte.com.cn) as least.
>
>> 5) document new procfs ksm knobs
>>
>> Signed-off-by: Stefan Roesch <shr@devkernel.io>
>> Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
>> Acked-by: David Hildenbrand <david@redhat.com>
>> Cc: David Hildenbrand <david@redhat.com>
>> Cc: Johannes Weiner <hannes@cmpxchg.org>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: Rik van Riel <riel@surriel.com>
>> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
>> ---
>>  Documentation/ABI/testing/sysfs-kernel-mm-ksm |  8 +++++++
>>  Documentation/admin-guide/mm/ksm.rst          |  5 ++++-
>>  fs/proc/base.c                                |  3 +++
>>  include/linux/ksm.h                           |  4 ++++
>>  mm/ksm.c                                      | 21 +++++++++++++++++++
>>  5 files changed, 40 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-ksm b/Documentation/ABI/testing/sysfs-kernel-mm-ksm
>> index d244674a9480..6041a025b65a 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:		April 2023
>> +KernelVersion:  6.4
>> +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