f2fs: export SSR allocation threshold

This patch exports min_ssr_segments threshold in sysfs to let user
control triggering SSR allocation flexibly.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 3e5877c..68ed6f9 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -181,7 +181,7 @@
 		return true;
 
 	return free_sections(sbi) <= (node_secs + 2 * dent_secs + imeta_secs +
-						2 * reserved_sections(sbi));
+			SM_I(sbi)->min_ssr_sections + reserved_sections(sbi));
 }
 
 void register_inmem_page(struct inode *inode, struct page *page)
@@ -3671,6 +3671,7 @@
 	sm_info->min_ipu_util = DEF_MIN_IPU_UTIL;
 	sm_info->min_fsync_blocks = DEF_MIN_FSYNC_BLOCKS;
 	sm_info->min_hot_blocks = DEF_MIN_HOT_BLOCKS;
+	sm_info->min_ssr_sections = reserved_sections(sbi);
 
 	sm_info->trim_sections = DEF_BATCHED_TRIM_SECTIONS;