f2fs: speed up gc_urgent mode with SSR

This patch activates SSR in gc_urgent mode.

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index c0803b1..9a7c903 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -2511,6 +2511,7 @@
 /*
  * segment.c
  */
+bool need_SSR(struct f2fs_sb_info *sbi);
 void register_inmem_page(struct inode *inode, struct page *page);
 void drop_inmem_pages(struct inode *inode);
 void drop_inmem_page(struct inode *inode, struct page *page);