[PATCH v4] fs/proc/page: Refactoring to reduce code duplication.

[Liu Ye <liuyerd@163.com>]

From: Liu Ye <liuye@kylinos.cn>

The function kpageflags_read and kpagecgroup_read is quite similar
to kpagecount_read. Consider refactoring common code into a helper
function to reduce code duplication.

Signed-off-by: Liu Ye <liuye@kylinos.cn>

---
V4 : Update code remake patch.
V3 : Add a stub for page_cgroup_ino and remove the #ifdef CONFIG_MEMCG.
V2 : Use an enumeration to indicate the operation to be performed
to avoid passing functions.
---
---
 fs/proc/page.c             | 161 +++++++++++++------------------------
 include/linux/memcontrol.h |   4 +
 2 files changed, 58 insertions(+), 107 deletions(-)

diff --git a/fs/proc/page.c b/fs/proc/page.c
index 23fc771100ae..999af26c7298 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -22,6 +22,12 @@
 #define KPMMASK (KPMSIZE - 1)
 #define KPMBITS (KPMSIZE * BITS_PER_BYTE)
 
+enum kpage_operation {
+	KPAGE_FLAGS,
+	KPAGE_COUNT,
+	KPAGE_CGROUP,
+};
+
 static inline unsigned long get_max_dump_pfn(void)
 {
 #ifdef CONFIG_SPARSEMEM
@@ -37,19 +43,17 @@ static inline unsigned long get_max_dump_pfn(void)
 #endif
 }
 
-/* /proc/kpagecount - an array exposing page mapcounts
- *
- * Each entry is a u64 representing the corresponding
- * physical page mapcount.
- */
-static ssize_t kpagecount_read(struct file *file, char __user *buf,
-			     size_t count, loff_t *ppos)
+static ssize_t kpage_read(struct file *file, char __user *buf,
+		size_t count, loff_t *ppos,
+		enum kpage_operation op)
 {
 	const unsigned long max_dump_pfn = get_max_dump_pfn();
 	u64 __user *out = (u64 __user *)buf;
+	struct page *page;
 	unsigned long src = *ppos;
 	unsigned long pfn;
 	ssize_t ret = 0;
+	u64 info;
 
 	pfn = src / KPMSIZE;
 	if (src & KPMMASK || count & KPMMASK)
@@ -59,24 +63,34 @@ static ssize_t kpagecount_read(struct file *file, char __user *buf,
 	count = min_t(unsigned long, count, (max_dump_pfn * KPMSIZE) - src);
 
 	while (count > 0) {
-		struct page *page;
-		u64 mapcount = 0;
-
 		/*
 		 * TODO: ZONE_DEVICE support requires to identify
 		 * memmaps that were actually initialized.
 		 */
 		page = pfn_to_online_page(pfn);
-		if (page) {
-			struct folio *folio = page_folio(page);
 
-			if (IS_ENABLED(CONFIG_PAGE_MAPCOUNT))
-				mapcount = folio_precise_page_mapcount(folio, page);
-			else
-				mapcount = folio_average_page_mapcount(folio);
-		}
-
-		if (put_user(mapcount, out)) {
+		if (page) {
+			switch (op) {
+			case KPAGE_FLAGS:
+				info = stable_page_flags(page);
+				break;
+			case KPAGE_COUNT:
+				if (IS_ENABLED(CONFIG_PAGE_MAPCOUNT))
+					info = folio_precise_page_mapcount(page_folio(page), page);
+				else
+					info = folio_average_page_mapcount(page_folio(page));
+				break;
+			case KPAGE_CGROUP:
+				info = page_cgroup_ino(page);
+				break;
+			default:
+				info = 0;
+				break;
+			}
+		} else
+			info = 0;
+
+		if (put_user(info, out)) {
 			ret = -EFAULT;
 			break;
 		}
@@ -94,17 +108,23 @@ static ssize_t kpagecount_read(struct file *file, char __user *buf,
 	return ret;
 }
 
+/* /proc/kpagecount - an array exposing page mapcounts
+ *
+ * Each entry is a u64 representing the corresponding
+ * physical page mapcount.
+ */
+static ssize_t kpagecount_read(struct file *file, char __user *buf,
+		size_t count, loff_t *ppos)
+{
+	return kpage_read(file, buf, count, ppos, KPAGE_COUNT);
+}
+
 static const struct proc_ops kpagecount_proc_ops = {
 	.proc_flags	= PROC_ENTRY_PERMANENT,
 	.proc_lseek	= mem_lseek,
 	.proc_read	= kpagecount_read,
 };
 
-/* /proc/kpageflags - an array exposing page flags
- *
- * Each entry is a u64 representing the corresponding
- * physical page flags.
- */
 
 static inline u64 kpf_copy_bit(u64 kflags, int ubit, int kbit)
 {
@@ -225,47 +245,17 @@ u64 stable_page_flags(const struct page *page)
 #endif
 
 	return u;
-};
+}
 
+/* /proc/kpageflags - an array exposing page flags
+ *
+ * Each entry is a u64 representing the corresponding
+ * physical page flags.
+ */
 static ssize_t kpageflags_read(struct file *file, char __user *buf,
-			     size_t count, loff_t *ppos)
+		size_t count, loff_t *ppos)
 {
-	const unsigned long max_dump_pfn = get_max_dump_pfn();
-	u64 __user *out = (u64 __user *)buf;
-	unsigned long src = *ppos;
-	unsigned long pfn;
-	ssize_t ret = 0;
-
-	pfn = src / KPMSIZE;
-	if (src & KPMMASK || count & KPMMASK)
-		return -EINVAL;
-	if (src >= max_dump_pfn * KPMSIZE)
-		return 0;
-	count = min_t(unsigned long, count, (max_dump_pfn * KPMSIZE) - src);
-
-	while (count > 0) {
-		/*
-		 * TODO: ZONE_DEVICE support requires to identify
-		 * memmaps that were actually initialized.
-		 */
-		struct page *page = pfn_to_online_page(pfn);
-
-		if (put_user(stable_page_flags(page), out)) {
-			ret = -EFAULT;
-			break;
-		}
-
-		pfn++;
-		out++;
-		count -= KPMSIZE;
-
-		cond_resched();
-	}
-
-	*ppos += (char __user *)out - buf;
-	if (!ret)
-		ret = (char __user *)out - buf;
-	return ret;
+	return kpage_read(file, buf, count, ppos, KPAGE_FLAGS);
 }
 
 static const struct proc_ops kpageflags_proc_ops = {
@@ -276,53 +266,10 @@ static const struct proc_ops kpageflags_proc_ops = {
 
 #ifdef CONFIG_MEMCG
 static ssize_t kpagecgroup_read(struct file *file, char __user *buf,
-				size_t count, loff_t *ppos)
+		size_t count, loff_t *ppos)
 {
-	const unsigned long max_dump_pfn = get_max_dump_pfn();
-	u64 __user *out = (u64 __user *)buf;
-	struct page *ppage;
-	unsigned long src = *ppos;
-	unsigned long pfn;
-	ssize_t ret = 0;
-	u64 ino;
-
-	pfn = src / KPMSIZE;
-	if (src & KPMMASK || count & KPMMASK)
-		return -EINVAL;
-	if (src >= max_dump_pfn * KPMSIZE)
-		return 0;
-	count = min_t(unsigned long, count, (max_dump_pfn * KPMSIZE) - src);
-
-	while (count > 0) {
-		/*
-		 * TODO: ZONE_DEVICE support requires to identify
-		 * memmaps that were actually initialized.
-		 */
-		ppage = pfn_to_online_page(pfn);
-
-		if (ppage)
-			ino = page_cgroup_ino(ppage);
-		else
-			ino = 0;
-
-		if (put_user(ino, out)) {
-			ret = -EFAULT;
-			break;
-		}
-
-		pfn++;
-		out++;
-		count -= KPMSIZE;
-
-		cond_resched();
-	}
-
-	*ppos += (char __user *)out - buf;
-	if (!ret)
-		ret = (char __user *)out - buf;
-	return ret;
+	return kpage_read(file, buf, count, ppos, KPAGE_CGROUP);
 }
-
 static const struct proc_ops kpagecgroup_proc_ops = {
 	.proc_flags	= PROC_ENTRY_PERMANENT,
 	.proc_lseek	= mem_lseek,
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 53364526d877..5264d148bdd9 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1793,6 +1793,10 @@ static inline void count_objcg_events(struct obj_cgroup *objcg,
 {
 }
 
+static inline ino_t page_cgroup_ino(struct page *page)
+{
+	return 0;
+}
 #endif /* CONFIG_MEMCG */
 
 #if defined(CONFIG_MEMCG) && defined(CONFIG_ZSWAP)
-- 
2.25.1