linux-kernel - [PATCH v4 4/6] ksm: count zero pages for each process

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Date:   Mon, 26 Dec 2022 10:05:52 +0800 (CST)
From:   <yang.yang29@....com.cn>
To:     <akpm@...ux-foundation.org>
Cc:     <david@...hat.com>, <imbrenda@...ux.ibm.com>,
        <jiang.xuexin@....com.cn>, <linux-kernel@...r.kernel.org>,
        <linux-mm@...ck.org>, <ran.xiaokai@....com.cn>,
        <xu.xin.sc@...il.com>, <xu.xin16@....com.cn>,
        <yang.yang29@....com.cn>
Subject: [PATCH v4 4/6] ksm: count zero pages for each process

From: xu xin <xu.xin16@....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.

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@...ux.ibm.com>
Cc: David Hildenbrand <david@...hat.com>
Cc: Xuexin Jiang <jiang.xuexin@....com.cn>
Cc: Xiaokai Ran <ran.xiaokai@....com.cn>
Cc: Yang Yang <yang.yang29@....com.cn>
Signed-off-by: xu xin <xu.xin16@....com.cn>
---
 fs/proc/base.c           | 1 +
 include/linux/mm_types.h | 7 ++++++-
 mm/ksm.c                 | 2 ++
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 9e479d7d202b..ac9ebe972be0 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, "zero_pages_sharing %lu\n", mm->ksm_zero_pages_sharing);
 		mmput(mm);
 	}

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 3b8475007734..9081cfe89d6f 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -776,7 +776,7 @@ struct mm_struct {
 #ifdef CONFIG_KSM
 		/*
 		 * Represent how many pages of this process are involved in KSM
-		 * merging.
+		 * merging (not including ksm_zero_pages_sharing).
 		 */
 		unsigned long ksm_merging_pages;
 		/*
@@ -784,6 +784,11 @@ struct mm_struct {
 		 * 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 {
diff --git a/mm/ksm.c b/mm/ksm.c
index e02cc89512cd..6eb85de7b69f 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -794,6 +794,7 @@ static inline void clean_rmap_item_zero_flag(struct ksm_rmap_item *rmap_item)
 {
 	if (rmap_item->address & ZERO_PAGE_FLAG) {
 		ksm_zero_pages_sharing--;
+		rmap_item->mm->ksm_zero_pages_sharing--;
 		rmap_item->address &= PAGE_MASK;
 	}
 }
@@ -2117,6 +2118,7 @@ static int try_to_merge_with_kernel_zero_page(struct ksm_rmap_item *rmap_item,
 			if (!err) {
 				rmap_item->address |= ZERO_PAGE_FLAG;
 				ksm_zero_pages_sharing++;
+				rmap_item->mm->ksm_zero_pages_sharing++;
 			}
 		} else {
 			/* If the vma is out of date, we do not need to continue. */
-- 
2.15.2