zsmalloc: introduce obj_allocated

The usage pattern for obj_to_head is to check whether the zpage is
allocated or not.  Thus, introduce obj_allocated.

Link: https://lkml.kernel.org/r/20211115185909.3949505-5-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: minchank

mm/zsmalloc.c

@@ -877,13 +877,21 @@ static unsigned long handle_to_obj(unsigned long handle)
 	return *(unsigned long *)handle;
 }
 
-static unsigned long obj_to_head(struct page *page, void *obj)
+static bool obj_allocated(struct page *page, void *obj, unsigned long *phandle)
 {
+	unsigned long handle;
+
 	if (unlikely(PageHugeObject(page))) {
 		VM_BUG_ON_PAGE(!is_first_page(page), page);
-		return page->index;
+		handle = page->index;
 	} else
-		return *(unsigned long *)obj;
+		handle = *(unsigned long *)obj;
+
+	if (!(handle & OBJ_ALLOCATED_TAG))
+		return false;
+
+	*phandle = handle & ~OBJ_ALLOCATED_TAG;
+	return true;
 }
 
 static inline int testpin_tag(unsigned long handle)
@@ -1606,7 +1614,6 @@ static void zs_object_copy(struct size_class *class, unsigned long dst,
 static unsigned long find_alloced_obj(struct size_class *class,
 					struct page *page, int *obj_idx)
 {
-	unsigned long head;
 	int offset = 0;
 	int index = *obj_idx;
 	unsigned long handle = 0;
@@ -1616,9 +1623,7 @@ static unsigned long find_alloced_obj(struct size_class *class,
 	offset += class->size * index;
 
 	while (offset < PAGE_SIZE) {
-		head = obj_to_head(page, addr + offset);
-		if (head & OBJ_ALLOCATED_TAG) {
-			handle = head & ~OBJ_ALLOCATED_TAG;
+		if (obj_allocated(page, addr + offset, &handle)) {
 			if (trypin_tag(handle))
 				break;
 			handle = 0;
@@ -1928,7 +1933,7 @@ static int zs_page_migrate(struct address_space *mapping, struct page *newpage,
 	struct page *dummy;
 	void *s_addr, *d_addr, *addr;
 	int offset, pos;
-	unsigned long handle, head;
+	unsigned long handle;
 	unsigned long old_obj, new_obj;
 	unsigned int obj_idx;
 	int ret = -EAGAIN;
@@ -1964,9 +1969,7 @@ static int zs_page_migrate(struct address_space *mapping, struct page *newpage,
 	pos = offset;
 	s_addr = kmap_atomic(page);
 	while (pos < PAGE_SIZE) {
-		head = obj_to_head(page, s_addr + pos);
-		if (head & OBJ_ALLOCATED_TAG) {
-			handle = head & ~OBJ_ALLOCATED_TAG;
+		if (obj_allocated(page, s_addr + pos, &handle)) {
 			if (!trypin_tag(handle))
 				goto unpin_objects;
 		}
@@ -1982,9 +1985,7 @@ static int zs_page_migrate(struct address_space *mapping, struct page *newpage,
 
 	for (addr = s_addr + offset; addr < s_addr + pos;
 					addr += class->size) {
-		head = obj_to_head(page, addr);
-		if (head & OBJ_ALLOCATED_TAG) {
-			handle = head & ~OBJ_ALLOCATED_TAG;
+		if (obj_allocated(page, addr, &handle)) {
 			BUG_ON(!testpin_tag(handle));
 
 			old_obj = handle_to_obj(handle);
@@ -2029,9 +2030,7 @@ static int zs_page_migrate(struct address_space *mapping, struct page *newpage,
 unpin_objects:
 	for (addr = s_addr + offset; addr < s_addr + pos;
 						addr += class->size) {
-		head = obj_to_head(page, addr);
-		if (head & OBJ_ALLOCATED_TAG) {
-			handle = head & ~OBJ_ALLOCATED_TAG;
+		if (obj_allocated(page, addr, &handle)) {
 			BUG_ON(!testpin_tag(handle));
 			unpin_tag(handle);
 		}