ksm: count zero pages for each process

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.

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
zero_pages_sharing in it.

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>
Signed-off-by: xu xin <xu.xin16@zte.com.cn>

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, "zero_pages_sharing %lu\n", mm->ksm_zero_pages_sharing);
 		mmput(mm);
 	}
 

include/linux/mm_types.h

@@ -691,14 +691,19 @@ struct mm_struct {
 #ifdef CONFIG_KSM
 		/*
 		 * Represent how many pages of this process are involved in KSM
-		 * merging.
+		 * merging (not including ksm_zero_pages_sharing).
 		 */
 		unsigned long ksm_merging_pages;
 		/*
 		 * Represent how many pages are checked for ksm merging
 		 * including merged and not merged.
 		 */
 		unsigned long ksm_rmap_items;
+		/*
+		 * Represent how many empty pages are merged with kernel zero
+		 * pages when enabling KSM use_zero_pages.
+		 */
+		unsigned long ksm_zero_pages_sharing;
 #endif
 #ifdef CONFIG_LRU_GEN
 		struct {

mm/ksm.c

@@ -547,6 +547,7 @@ static inline void free_rmap_item(struct ksm_rmap_item *rmap_item)
 	if (rmap_item->address & ZERO_PAGE_FLAG) {
 		if (!unshare_zero_pages(rmap_item))
 			ksm_zero_pages_sharing--;
+			rmap_item->mm->ksm_zero_pages_sharing--;
 	}
 	ksm_rmap_items--;
 	rmap_item->mm->ksm_rmap_items--;
@@ -2082,6 +2083,7 @@ static int try_to_merge_with_kernel_zero_page(struct mm_struct *mm,
 		if (!err) {
 			rmap_item->address |= ZERO_PAGE_FLAG;
 			ksm_zero_pages_sharing++;
+			rmap_item->mm->ksm_zero_pages_sharing++;
 		}
 	}
 
@@ -2185,6 +2187,7 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite
 			 */
 			rmap_item->address &= PAGE_MASK;
 			ksm_zero_pages_sharing--;
+			rmap_item->mm->ksm_zero_pages_sharing--;
 		}
 	}