[PATCH v10 0/5] ksm: support tracking KSM-placed zero-pages

[PATCH v10 0/5] ksm: support tracking KSM-placed zero-pages

[yang.yang29]

From: xu xin <xu.xin16@zte.com.cn>

The core idea of this patch set is to enable users to perceive the number
of any pages merged by KSM, regardless of whether use_zero_page switch has
been turned on, so that users can know how much free memory increase is
really due to their madvise(MERGEABLE) actions. But the problem is, when
enabling use_zero_pages, all empty pages will be merged with kernel zero
pages instead of with each other as use_zero_pages is disabled, and then
these zero-pages are no longer monitored by KSM.

The motivations to do this is seen at:
https://lore.kernel.org/lkml/202302100915227721315@zte.com.cn/

In one word, we hope to implement the support for KSM-placed zero pages
tracking without affecting the feature of use_zero_pages, so that app
developer can also benefit from knowing the actual KSM profit by getting
KSM-placed zero pages to optimize applications eventually when
/sys/kernel/mm/ksm/use_zero_pages is enabled.

Change log
----------
v9->v10:
-------
(1) Fix a compile error due to [PATCH v8 3/5] when CONFIG_KSM is not set.

(2) Rename the function 'ksm_notify_unmap_zero_page' as
    'ksm_might_unmap_zero_page'.

(3) In [PATCH 5/5], we get ksm_zero_pages from its own 'mm' instead of
	the global system.

(4) In [PATCH 5/5], we add a subject task of testing ksm zero pages when
	unmerging by triggering write fault.

v8->v9:
------
(1) The previous [PATCH v8 4/6] is squashed into the current [PATCH v9 2/5].

(2) Improve the codes as David's suggestions.

v7->v8:
-------
(1) Since [1] which fix the bug of pte_mkdirty on sparc64 that makes pte
    writable, then we can remove the architechture restrictions of our
	features.
(2) Improve the scheme of update ksm_zero_pages: add the handling case when
    khugepaged replaces a shared zeropage by a THP. 

[1] https://lore.kernel.org/all/20230411141529.428991-2-david@redhat.com/

v6->v7:
-------
This is an all-newed version which is different from v6 which relys on KSM's
rmap_item. The patch series don't rely on rmap_item but pte_dirty, so the
general handling of tracking KSM-placed zero-pages is simplified a lot.

For safety, we restrict this feature only to the tested and known-working
architechtures (ARM, ARM64, and X86) fow now.

xu xin (5):
  ksm: support unsharing KSM-placed zero pages
  ksm: count all zero pages placed by KSM
  ksm: add ksm zero pages for each process
  ksm: consider KSM-placed zeropages when calculating KSM profit
  selftest: add a testcase of ksm zero pages

 Documentation/admin-guide/mm/ksm.rst              | 25 ++++--
 fs/proc/base.c                                    |  1 +
 include/linux/ksm.h                               | 20 +++++
 include/linux/mm_types.h                          |  9 ++-
 mm/khugepaged.c                                   |  2 +
 mm/ksm.c                                          | 28 +++++--
 mm/memory.c                                       |  5 +-
 tools/testing/selftests/mm/ksm_functional_tests.c | 98 ++++++++++++++++++++++-
 8 files changed, 172 insertions(+), 16 deletions(-)

-- 
2.15.2

[PATCH v10 1/5] ksm: support unsharing KSM-placed zero pages

[Yang Yang]

From: xu xin <xu.xin16@zte.com.cn>

When use_zero_pages of ksm is enabled, madvise(addr, len, MADV_UNMERGEABLE)
and other ways (like write 2 to /sys/kernel/mm/ksm/run) to trigger
unsharing will *not* actually unshare the shared zeropage as placed by KSM
(which is against the MADV_UNMERGEABLE documentation). As these KSM-placed
zero pages are out of the control of KSM, the related counts of ksm pages
don't expose how many zero pages are placed by KSM (these special zero
pages are different from those initially mapped zero pages, because the
zero pages mapped to MADV_UNMERGEABLE areas are expected to be a complete
and unshared page).

To not blindly unshare all shared zero_pages in applicable VMAs, the patch
use pte_mkdirty (related with architecture) to mark KSM-placed zero pages.
Thus, MADV_UNMERGEABLE will only unshare those KSM-placed zero pages.

In addition, we'll reuse this mechanism to reliably identify KSM-placed
ZeroPages to properly account for them (e.g., calculating the KSM profit
that includes zeropages) in the latter patches.

The patch will not degrade the performance of use_zero_pages as it doesn't
change the way of merging empty pages in use_zero_pages's feature.

Signed-off-by: xu xin <xu.xin16@zte.com.cn>
Suggested-by: David Hildenbrand <david@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Xiaokai Ran <ran.xiaokai@zte.com.cn>
Reviewed-by: Yang Yang <yang.yang29@zte.com.cn>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Xuexin Jiang <jiang.xuexin@zte.com.cn>
---
 include/linux/ksm.h |  6 ++++++
 mm/ksm.c            | 11 ++++++++---
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 899a314bc487..98878107244f 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -26,6 +26,12 @@ int ksm_disable(struct mm_struct *mm);
 
 int __ksm_enter(struct mm_struct *mm);
 void __ksm_exit(struct mm_struct *mm);
+/*
+ * To identify zeropages that were mapped by KSM, we reuse the dirty bit
+ * in the PTE. If the PTE is dirty, the zeropage was mapped by KSM when
+ * deduplicating memory.
+ */
+#define is_ksm_zero_pte(pte)	(is_zero_pfn(pte_pfn(pte)) && pte_dirty(pte))
 
 static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
 {
diff --git a/mm/ksm.c b/mm/ksm.c
index 0156bded3a66..f31c789406b1 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -447,7 +447,8 @@ static int break_ksm_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long nex
 		if (is_migration_entry(entry))
 			page = pfn_swap_entry_to_page(entry);
 	}
-	ret = page && PageKsm(page);
+	/* return 1 if the page is an normal ksm page or KSM-placed zero page */
+	ret = (page && PageKsm(page)) || is_ksm_zero_pte(*pte);
 	pte_unmap_unlock(pte, ptl);
 	return ret;
 }
@@ -1220,8 +1221,12 @@ static int replace_page(struct vm_area_struct *vma, struct page *page,
 		page_add_anon_rmap(kpage, vma, addr, RMAP_NONE);
 		newpte = mk_pte(kpage, vma->vm_page_prot);
 	} else {
-		newpte = pte_mkspecial(pfn_pte(page_to_pfn(kpage),
-					       vma->vm_page_prot));
+		/*
+		 * Use pte_mkdirty to mark the zero page mapped by KSM, and then
+		 * we can easily track all KSM-placed zero pages by checking if
+		 * the dirty bit in zero page's PTE is set.
+		 */
+		newpte = pte_mkdirty(pte_mkspecial(pfn_pte(page_to_pfn(kpage), vma->vm_page_prot)));
 		/*
 		 * We're replacing an anonymous page with a zero page, which is
 		 * not anonymous. We need to do proper accounting otherwise we
-- 
2.15.2

[PATCH v10 2/5] ksm: count all zero pages placed by KSM

[Yang Yang]

From: xu xin <xu.xin16@zte.com.cn>

As pages_sharing and pages_shared don't include the number of zero pages
merged by KSM, we cannot know how many pages are zero pages placed by KSM
when enabling use_zero_pages, which leads to KSM not being transparent with
all actual merged pages by KSM. In the early days of use_zero_pages,
zero-pages was unable to get unshared by the ways like MADV_UNMERGEABLE so
it's hard to count how many times one of those zeropages was then unmerged.

But now, unsharing KSM-placed zero page accurately has been achieved, so we
can easily count both how many times a page full of zeroes was merged with
zero-page and how many times one of those pages was then unmerged. and so,
it helps to estimate memory demands when each and every shared page could
get unshared.

So we add ksm_zero_pages under /sys/kernel/mm/ksm/ to show the number
of all zero pages placed by KSM. Meanwhile, we update the Documentation.

Signed-off-by: xu xin <xu.xin16@zte.com.cn>
Suggested-by: David Hildenbrand <david@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Xiaokai Ran <ran.xiaokai@zte.com.cn>
Reviewed-by: Yang Yang <yang.yang29@zte.com.cn>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Xuexin Jiang <jiang.xuexin@zte.com.cn>
---
 Documentation/admin-guide/mm/ksm.rst |  7 +++++++
 include/linux/ksm.h                  | 12 ++++++++++++
 mm/khugepaged.c                      |  2 ++
 mm/ksm.c                             | 12 ++++++++++++
 mm/memory.c                          |  5 ++++-
 5 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst
index 7626392fe82c..6cc919dbfd55 100644
--- a/Documentation/admin-guide/mm/ksm.rst
+++ b/Documentation/admin-guide/mm/ksm.rst
@@ -173,6 +173,13 @@ stable_node_chains
         the number of KSM pages that hit the ``max_page_sharing`` limit
 stable_node_dups
         number of duplicated KSM pages
+ksm_zero_pages
+        how many zero pages that are still mapped into processes were mapped by
+        KSM when deduplicating.
+
+When ``use_zero_pages`` is/was enabled, the sum of ``pages_sharing`` +
+``ksm_zero_pages`` represents the actual number of pages saved by KSM.
+if ``use_zero_pages`` has never been enabled, ``ksm_zero_pages`` is 0.
 
 A high ratio of ``pages_sharing`` to ``pages_shared`` indicates good
 sharing, but a high ratio of ``pages_unshared`` to ``pages_sharing``
diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 98878107244f..e80aa49009b2 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -33,6 +33,14 @@ void __ksm_exit(struct mm_struct *mm);
  */
 #define is_ksm_zero_pte(pte)	(is_zero_pfn(pte_pfn(pte)) && pte_dirty(pte))
 
+extern unsigned long ksm_zero_pages;
+
+static inline void ksm_might_unmap_zero_page(pte_t pte)
+{
+	if (is_ksm_zero_pte(pte))
+		ksm_zero_pages--;
+}
+
 static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
 {
 	int ret;
@@ -101,6 +109,10 @@ static inline void ksm_exit(struct mm_struct *mm)
 {
 }
 
+static inline void ksm_might_unmap_zero_page(pte_t pte)
+{
+}
+
 #ifdef CONFIG_MEMORY_FAILURE
 static inline void collect_procs_ksm(struct page *page,
 				     struct list_head *to_kill, int force_early)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 6b9d39d65b73..3f293e2436f3 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -19,6 +19,7 @@
 #include <linux/page_table_check.h>
 #include <linux/swapops.h>
 #include <linux/shmem_fs.h>
+#include <linux/ksm.h>
 
 #include <asm/tlb.h>
 #include <asm/pgalloc.h>
@@ -711,6 +712,7 @@ static void __collapse_huge_page_copy_succeeded(pte_t *pte,
 				spin_lock(ptl);
 				ptep_clear(vma->vm_mm, address, _pte);
 				spin_unlock(ptl);
+				ksm_might_unmap_zero_page(pteval);
 			}
 		} else {
 			src_page = pte_page(pteval);
diff --git a/mm/ksm.c b/mm/ksm.c
index f31c789406b1..d3ed90159322 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -278,6 +278,9 @@ static unsigned int zero_checksum __read_mostly;
 /* Whether to merge empty (zeroed) pages with actual zero pages */
 static bool ksm_use_zero_pages __read_mostly;
 
+/* The number of zero pages which is placed by KSM */
+unsigned long ksm_zero_pages;
+
 #ifdef CONFIG_NUMA
 /* Zeroed when merging across nodes is not allowed */
 static unsigned int ksm_merge_across_nodes = 1;
@@ -1227,6 +1230,7 @@ static int replace_page(struct vm_area_struct *vma, struct page *page,
 		 * the dirty bit in zero page's PTE is set.
 		 */
 		newpte = pte_mkdirty(pte_mkspecial(pfn_pte(page_to_pfn(kpage), vma->vm_page_prot)));
+		ksm_zero_pages++;
 		/*
 		 * We're replacing an anonymous page with a zero page, which is
 		 * not anonymous. We need to do proper accounting otherwise we
@@ -3354,6 +3358,13 @@ static ssize_t pages_volatile_show(struct kobject *kobj,
 }
 KSM_ATTR_RO(pages_volatile);
 
+static ssize_t ksm_zero_pages_show(struct kobject *kobj,
+				struct kobj_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%ld\n", ksm_zero_pages);
+}
+KSM_ATTR_RO(ksm_zero_pages);
+
 static ssize_t general_profit_show(struct kobject *kobj,
 				   struct kobj_attribute *attr, char *buf)
 {
@@ -3421,6 +3432,7 @@ static struct attribute *ksm_attrs[] = {
 	&pages_sharing_attr.attr,
 	&pages_unshared_attr.attr,
 	&pages_volatile_attr.attr,
+	&ksm_zero_pages_attr.attr,
 	&full_scans_attr.attr,
 #ifdef CONFIG_NUMA
 	&merge_across_nodes_attr.attr,
diff --git a/mm/memory.c b/mm/memory.c
index 8358f3b853f2..15e6bd757eab 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1415,8 +1415,10 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
 			tlb_remove_tlb_entry(tlb, pte, addr);
 			zap_install_uffd_wp_if_needed(vma, addr, pte, details,
 						      ptent);
-			if (unlikely(!page))
+			if (unlikely(!page)) {
+				ksm_might_unmap_zero_page(ptent);
 				continue;
+			}
 
 			delay_rmap = 0;
 			if (!PageAnon(page)) {
@@ -3120,6 +3122,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
 				inc_mm_counter(mm, MM_ANONPAGES);
 			}
 		} else {
+			ksm_might_unmap_zero_page(vmf->orig_pte);
 			inc_mm_counter(mm, MM_ANONPAGES);
 		}
 		flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
-- 
2.15.2

[PATCH v10 3/5] ksm: add ksm zero pages for each process

[Yang Yang]

From: xu xin <xu.xin16@zte.com.cn>

As the number of ksm zero pages is not included in ksm_merging_pages per
process when enabling use_zero_pages, it's unclear of how many actual
pages are merged by KSM. To let users accurately estimate their memory
demands when unsharing KSM zero-pages, it's necessary to show KSM zero-
pages per process. In addition, it help users to know the actual KSM
profit because KSM-placed zero pages are also benefit from KSM.

since unsharing zero pages placed by KSM accurately is achieved, then
tracking empty pages merging and unmerging is not a difficult thing any
longer.

Since we already have /proc/<pid>/ksm_stat, just add the information of
'ksm_zero_pages' in it.

Signed-off-by: xu xin <xu.xin16@zte.com.cn>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Xuexin Jiang <jiang.xuexin@zte.com.cn>
Cc: Xiaokai Ran <ran.xiaokai@zte.com.cn>
Cc: Yang Yang <yang.yang29@zte.com.cn>
---
 fs/proc/base.c           | 1 +
 include/linux/ksm.h      | 8 +++++---
 include/linux/mm_types.h | 9 +++++++--
 mm/khugepaged.c          | 2 +-
 mm/ksm.c                 | 1 +
 mm/memory.c              | 4 ++--
 6 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 05452c3b9872..eb2e498e3b8d 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3207,6 +3207,7 @@ 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_zero_pages %lu\n", mm->ksm_zero_pages);
 		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 e80aa49009b2..c2dd786a30e1 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -35,10 +35,12 @@ void __ksm_exit(struct mm_struct *mm);
 
 extern unsigned long ksm_zero_pages;
 
-static inline void ksm_might_unmap_zero_page(pte_t pte)
+static inline void ksm_might_unmap_zero_page(struct mm_struct *mm, pte_t pte)
 {
-	if (is_ksm_zero_pte(pte))
+	if (is_ksm_zero_pte(pte)) {
 		ksm_zero_pages--;
+		mm->ksm_zero_pages--;
+	}
 }
 
 static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
@@ -109,7 +111,7 @@ static inline void ksm_exit(struct mm_struct *mm)
 {
 }
 
-static inline void ksm_might_unmap_zero_page(pte_t pte)
+static inline void ksm_might_unmap_zero_page(struct mm_struct *mm, pte_t pte)
 {
 }
 
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 306a3d1a0fa6..14f781509812 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -777,7 +777,7 @@ struct mm_struct {
 #ifdef CONFIG_KSM
 		/*
 		 * Represent how many pages of this process are involved in KSM
-		 * merging.
+		 * merging (not including ksm_zero_pages).
 		 */
 		unsigned long ksm_merging_pages;
 		/*
@@ -785,7 +785,12 @@ struct mm_struct {
 		 * including merged and not merged.
 		 */
 		unsigned long ksm_rmap_items;
-#endif
+		/*
+		 * Represent how many empty pages are merged with kernel zero
+		 * pages when enabling KSM use_zero_pages.
+		 */
+		unsigned long ksm_zero_pages;
+#endif /* CONFIG_KSM */
 #ifdef CONFIG_LRU_GEN
 		struct {
 			/* this mm_struct is on lru_gen_mm_list */
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 3f293e2436f3..225d98744d2e 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -712,7 +712,7 @@ static void __collapse_huge_page_copy_succeeded(pte_t *pte,
 				spin_lock(ptl);
 				ptep_clear(vma->vm_mm, address, _pte);
 				spin_unlock(ptl);
-				ksm_might_unmap_zero_page(pteval);
+				ksm_might_unmap_zero_page(vma->vm_mm, pteval);
 			}
 		} else {
 			src_page = pte_page(pteval);
diff --git a/mm/ksm.c b/mm/ksm.c
index d3ed90159322..07a6fe7d7c99 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1231,6 +1231,7 @@ static int replace_page(struct vm_area_struct *vma, struct page *page,
 		 */
 		newpte = pte_mkdirty(pte_mkspecial(pfn_pte(page_to_pfn(kpage), vma->vm_page_prot)));
 		ksm_zero_pages++;
+		mm->ksm_zero_pages++;
 		/*
 		 * We're replacing an anonymous page with a zero page, which is
 		 * not anonymous. We need to do proper accounting otherwise we
diff --git a/mm/memory.c b/mm/memory.c
index 15e6bd757eab..811a98fb403e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1416,7 +1416,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
 			zap_install_uffd_wp_if_needed(vma, addr, pte, details,
 						      ptent);
 			if (unlikely(!page)) {
-				ksm_might_unmap_zero_page(ptent);
+				ksm_might_unmap_zero_page(mm, ptent);
 				continue;
 			}
 
@@ -3122,7 +3122,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
 				inc_mm_counter(mm, MM_ANONPAGES);
 			}
 		} else {
-			ksm_might_unmap_zero_page(vmf->orig_pte);
+			ksm_might_unmap_zero_page(mm, vmf->orig_pte);
 			inc_mm_counter(mm, MM_ANONPAGES);
 		}
 		flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
-- 
2.15.2

[PATCH v10 4/5] ksm: consider KSM-placed zeropages when calculating KSM profit

[Yang Yang]

From: xu xin <xu.xin16@zte.com.cn>

When use_zero_pages is enabled, the calculation of ksm profit is not
correct because ksm zero pages is not counted in. So update the
calculation of KSM profit including the documentation.

Signed-off-by: xu xin <xu.xin16@zte.com.cn>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Xiaokai Ran <ran.xiaokai@zte.com.cn>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Cc: Jiang Xuexin <jiang.xuexin@zte.com.cn>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
 Documentation/admin-guide/mm/ksm.rst | 18 +++++++++++-------
 mm/ksm.c                             |  4 ++--
 2 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst
index 6cc919dbfd55..5c5be7bd84b8 100644
--- a/Documentation/admin-guide/mm/ksm.rst
+++ b/Documentation/admin-guide/mm/ksm.rst
@@ -203,21 +203,25 @@ several times, which are unprofitable memory consumed.
 1) How to determine whether KSM save memory or consume memory in system-wide
    range? Here is a simple approximate calculation for reference::
 
-	general_profit =~ pages_sharing * sizeof(page) - (all_rmap_items) *
+	general_profit =~ ksm_saved_pages * sizeof(page) - (all_rmap_items) *
 			  sizeof(rmap_item);
 
-   where all_rmap_items can be easily obtained by summing ``pages_sharing``,
-   ``pages_shared``, ``pages_unshared`` and ``pages_volatile``.
+   where ksm_saved_pages equals to the sum of ``pages_sharing`` +
+   ``ksm_zero_pages`` of the system, and all_rmap_items can be easily
+   obtained by summing ``pages_sharing``, ``pages_shared``, ``pages_unshared``
+   and ``pages_volatile``.
 
 2) The KSM profit inner a single process can be similarly obtained by the
    following approximate calculation::
 
-	process_profit =~ ksm_merging_pages * sizeof(page) -
+	process_profit =~ ksm_saved_pages * sizeof(page) -
 			  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``. The process profit
-   is also shown in ``/proc/<pid>/ksm_stat`` as ksm_process_profit.
+   where ksm_saved_pages equals to the sum of ``ksm_merging_pages`` and
+   ``ksm_zero_pages``, both of which are shown under the directory
+   ``/proc/<pid>/ksm_stat``, and ksm_rmap_items is also 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/mm/ksm.c b/mm/ksm.c
index 07a6fe7d7c99..1c7d0e215c47 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -3090,7 +3090,7 @@ static void wait_while_offlining(void)
 #ifdef CONFIG_PROC_FS
 long ksm_process_profit(struct mm_struct *mm)
 {
-	return mm->ksm_merging_pages * PAGE_SIZE -
+	return (long)(mm->ksm_merging_pages + mm->ksm_zero_pages) * PAGE_SIZE -
 		mm->ksm_rmap_items * sizeof(struct ksm_rmap_item);
 }
 #endif /* CONFIG_PROC_FS */
@@ -3371,7 +3371,7 @@ static ssize_t general_profit_show(struct kobject *kobj,
 {
 	long general_profit;
 
-	general_profit = ksm_pages_sharing * PAGE_SIZE -
+	general_profit = (ksm_pages_sharing + ksm_zero_pages) * PAGE_SIZE -
 				ksm_rmap_items * sizeof(struct ksm_rmap_item);
 
 	return sysfs_emit(buf, "%ld\n", general_profit);
-- 
2.15.2

[PATCH v10 5/5] selftest: add a testcase of ksm zero pages

[Yang Yang]

From: xu xin <xu.xin16@zte.com.cn>

Add a function test_unmerge_zero_page() to test the functionality on
unsharing and counting ksm-placed zero pages and counting of this patch
series.

test_unmerge_zero_page() actually contains four subjct test objects:
(1) whether the count of ksm zero pages can update correctly after merging;
(2) whether the count of ksm zero pages can update correctly after
    unmerging by madvise(...MADV_UNMERGEABLE);
(3) whether the count of ksm zero pages can update correctly after
	unmerging by triggering write fault.
(4) whether ksm zero pages are really unmerged.

Signed-off-by: xu xin <xu.xin16@zte.com.cn>
Reviewed-by: Xiaokai Ran <ran.xiaokai@zte.com.cn>
Reviewed-by: Yang Yang <yang.yang29@zte.com.cn>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Xuexin Jiang <jiang.xuexin@zte.com.cn>
---
 tools/testing/selftests/mm/ksm_functional_tests.c | 98 ++++++++++++++++++++++-
 1 file changed, 97 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
index 26853badae70..0de9d33cd565 100644
--- a/tools/testing/selftests/mm/ksm_functional_tests.c
+++ b/tools/testing/selftests/mm/ksm_functional_tests.c
@@ -29,6 +29,8 @@
 
 static int ksm_fd;
 static int ksm_full_scans_fd;
+static int proc_self_ksm_stat_fd;
+static int ksm_use_zero_pages_fd;
 static int pagemap_fd;
 static size_t pagesize;
 
@@ -59,6 +61,33 @@ static bool range_maps_duplicates(char *addr, unsigned long size)
 	return false;
 }
 
+static long get_my_ksm_zero_pages(void)
+{
+	char buf[200];
+	char *substr_ksm_zero;
+	size_t value_pos;
+	ssize_t read_size;
+	unsigned long my_ksm_zero_pages;
+
+	if (!proc_self_ksm_stat_fd)
+		return 0;
+
+	read_size = pread(proc_self_ksm_stat_fd, buf, sizeof(buf) - 1, 0);
+	if (read_size < 0)
+		return -errno;
+
+	buf[read_size] = 0;
+
+	substr_ksm_zero = strstr(buf, "ksm_zero_pages");
+	if (!substr_ksm_zero)
+		return 0;
+
+	value_pos = strcspn(substr_ksm_zero, "0123456789");
+	my_ksm_zero_pages = strtol(substr_ksm_zero + value_pos, NULL, 10);
+
+	return my_ksm_zero_pages;
+}
+
 static long ksm_get_full_scans(void)
 {
 	char buf[10];
@@ -159,6 +188,70 @@ static void test_unmerge(void)
 	munmap(map, size);
 }
 
+static void test_unmerge_zero_pages(void)
+{
+	const unsigned int size = 2 * MiB;
+	char *map;
+	unsigned int offs;
+	unsigned long pages_expected;
+
+	ksft_print_msg("[RUN] %s\n", __func__);
+
+	if (proc_self_ksm_stat_fd < 0) {
+		ksft_test_result_skip("open(\"/proc/self/ksm_stat\") failed\n");
+		return;
+	}
+	if (ksm_use_zero_pages_fd < 0) {
+		ksft_test_result_skip("open \"/sys/kernel/mm/ksm/use_zero_pages\" failed\n");
+		return;
+	}
+	if (write(ksm_use_zero_pages_fd, "1", 1) != 1) {
+		ksft_test_result_skip("write \"/sys/kernel/mm/ksm/use_zero_pages\" failed\n");
+		return;
+	}
+
+	/* Let KSM deduplicate zero pages. */
+	map = mmap_and_merge_range(0x00, size, false);
+	if (map == MAP_FAILED)
+		return;
+
+	/* Check if ksm_zero_pages is updated correctly after KSM merging */
+	pages_expected = size / pagesize;
+	if (pages_expected != get_my_ksm_zero_pages()) {
+		ksft_test_result_fail("'ksm_zero_pages' updated after merging\n");
+		goto unmap;
+	}
+
+	/* Try to unmerge half of the region */
+	if (madvise(map, size / 2, MADV_UNMERGEABLE)) {
+		ksft_test_result_fail("MADV_UNMERGEABLE failed\n");
+		goto unmap;
+	}
+
+	/* Check if ksm_zero_pages is updated correctly after unmerging */
+	pages_expected /= 2;
+	if (pages_expected != get_my_ksm_zero_pages()) {
+		ksft_test_result_fail("'ksm_zero_pages' updated after unmerging\n");
+		goto unmap;
+	}
+
+	/* Trigger unmerging of the other half by writing to the pages. */
+	for (offs = size / 2; offs < size; offs += pagesize)
+		*((unsigned int *)&map[offs]) = offs;
+
+	/* Now we should have no zeropages remaining. */
+	if (get_my_ksm_zero_pages()) {
+		ksft_test_result_fail("'ksm_zero_pages' updated after write fault\n");
+		goto unmap;
+	}
+
+	/* Check if ksm zero pages are really unmerged */
+	ksft_test_result(!range_maps_duplicates(map, size),
+			"KSM zero pages were unmerged\n");
+unmap:
+	munmap(map, size);
+}
+
 static void test_unmerge_discarded(void)
 {
 	const unsigned int size = 2 * MiB;
@@ -358,7 +451,7 @@ static void test_prctl_unmerge(void)
 
 int main(int argc, char **argv)
 {
-	unsigned int tests = 5;
+	unsigned int tests = 6;
 	int err;
 
 #ifdef __NR_userfaultfd
@@ -379,8 +472,11 @@ int main(int argc, char **argv)
 	pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
 	if (pagemap_fd < 0)
 		ksft_exit_skip("open(\"/proc/self/pagemap\") failed\n");
+	proc_self_ksm_stat_fd = open("/proc/self/ksm_stat", O_RDONLY);
+	ksm_use_zero_pages_fd = open("/sys/kernel/mm/ksm/use_zero_pages", O_RDWR);
 
 	test_unmerge();
+	test_unmerge_zero_pages();
 	test_unmerge_discarded();
 #ifdef __NR_userfaultfd
 	test_unmerge_uffd_wp();
-- 
2.15.2

Re: [PATCH v10 5/5] selftest: add a testcase of ksm zero pages

[David Hildenbrand]

On 25.05.23 07:54, Yang Yang wrote:
> From: xu xin <xu.xin16@zte.com.cn>
> 
> Add a function test_unmerge_zero_page() to test the functionality on
> unsharing and counting ksm-placed zero pages and counting of this patch
> series.
> 
> test_unmerge_zero_page() actually contains four subjct test objects:
> (1) whether the count of ksm zero pages can update correctly after merging;
> (2) whether the count of ksm zero pages can update correctly after
>      unmerging by madvise(...MADV_UNMERGEABLE);
> (3) whether the count of ksm zero pages can update correctly after
> 	unmerging by triggering write fault.
> (4) whether ksm zero pages are really unmerged.
> 
> Signed-off-by: xu xin <xu.xin16@zte.com.cn>
> Reviewed-by: Xiaokai Ran <ran.xiaokai@zte.com.cn>
> Reviewed-by: Yang Yang <yang.yang29@zte.com.cn>
> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Xuexin Jiang <jiang.xuexin@zte.com.cn>
> ---

Acked-by: David Hildenbrand <david@redhat.com>

Thanks!

-- 
Thanks,

David / dhildenb