[PATCH v2] zsmalloc: zs_page_migrate: schedule free_work if zspage is ZS_EMPTY

[Hui Zhu <zhuhui@xiaomi.com>]

After commit e2846124f9a2 ("zsmalloc: zs_page_migrate: skip unnecessary
loops but not return -EBUSY if zspage is not inuse") zs_page_migrate
can handle the ZS_EMPTY zspage.

But I got some false in zs_page_isolate:
	if (get_zspage_inuse(zspage) == 0) {
		spin_unlock(&class->lock);
		return false;
	}
The page of this zspage was migrated in before.

The reason is commit e2846124f9a2 ("zsmalloc: zs_page_migrate: skip
unnecessary loops but not return -EBUSY if zspage is not inuse") just
handle the "page" but not "newpage" then it keep the "newpage" with
a empty zspage inside system.
Root cause is zs_page_isolate remove it from ZS_EMPTY list but not
call zs_page_putback "schedule_work(&pool->free_work);".  Because
zs_page_migrate done the job without "schedule_work(&pool->free_work);"

Make this patch let zs_page_migrate wake up free_work if need.

Fixes: e2846124f9a2 ("zsmalloc: zs_page_migrate: skip unnecessary loops but not return -EBUSY if zspage is not inuse")
Signed-off-by: Hui Zhu <zhuhui@xiaomi.com>
---
 mm/zsmalloc.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 62457eb..c6cc77c 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -2035,8 +2035,17 @@ int zs_page_migrate(struct address_space *mapping, struct page *newpage,
 	 * Page migration is done so let's putback isolated zspage to
 	 * the list if @page is final isolated subpage in the zspage.
 	 */
-	if (!is_zspage_isolated(zspage))
-		putback_zspage(class, zspage);
+	if (!is_zspage_isolated(zspage)) {
+		/*
+		 * Page will be freed in following part. But newpage and
+		 * zspage will stay in system if zspage is in ZS_EMPTY
+		 * list.  So call free_work to free it.
+		 * The page and class is locked, we cannot free zspage
+		 * immediately so let's defer.
+		 */
+		if (putback_zspage(class, zspage) == ZS_EMPTY)
+			schedule_work(&pool->free_work);
+	}
 
 	reset_page(page);
 	put_page(page);
-- 
1.9.1

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