diff --git a/components/fs/kv/include/tos_kv.h b/components/fs/kv/include/tos_kv.h
index 8d97ea09..0cf8b1cb 100644
--- a/components/fs/kv/include/tos_kv.h
+++ b/components/fs/kv/include/tos_kv.h
@@ -81,7 +81,7 @@ typedef uint64_t    kv_dword_t; // double word
 
 #define KV_NO_WRITEABLE_BLK()                       (KV_MGR_BLK_NUM_INUSE == 0 && KV_MGR_BLK_NUM_FRESH == 0)
 
-#define KV_ITEM_HDR_MAGIC                           0xABCD1234DCBA4321
+#define KV_ITEM_HDR_MAGIC                           0x69745F6D61676963 /* "it_magic" */
 #define KV_ITEM_DISCARDED                           0x0F0F0F0F0F0F0F0F
 #define KV_ITEM_IS_DISCARDED(item_hdr)              ((item_hdr)->discarded_flag == KV_ITEM_DISCARDED)
 #define KV_ITEM_IS_LEGAL(item_hdr)                  ((item_hdr)->magic == KV_ITEM_HDR_MAGIC)
@@ -100,10 +100,10 @@ typedef uint64_t    kv_dword_t; // double word
 #define KV_ITEM_SIZE_OF_BODY(item)                  KV_ITEM_BODY_SIZE(item->hdr.k_len, item->hdr.v_len)
 #define KV_ITEM_ADDR_OF_BODY(item)                  (item->pos + KV_ITEM_HDR_SIZE)
 
-#define KV_BLK_HDR_MAGIC                            0x1234ABCD4321DCBA
-#define KV_BLK_HDR_GC_SRC                           0x5678DCBA8765ABCD
-#define KV_BLK_HDR_GC_DST                           0x8765ABCD8765DCBA
-#define KV_BLK_HDR_GC_DONE                          0x4321DCBA1234ABCD
+#define KV_BLK_HDR_MAGIC                            0x48445F4D41474943 /* "HD_MAGIC" */
+#define KV_BLK_HDR_GC_SRC                           0x6D61726B5F737263 /* "mark_src" */
+#define KV_BLK_HDR_GC_DST                           0x6D61726B5F647374 /* "mark_dst" */
+#define KV_BLK_HDR_GC_DONE                          0x6B67635F646F6E65 /* "kgc_done" */
 
 #define KV_BLK_IS_LEGAL(blk_hdr)                    ((blk_hdr)->magic == KV_BLK_HDR_MAGIC)
 
@@ -196,7 +196,7 @@ typedef struct kv_item_st {
     uint8_t        *body;       /*< item body: key/value buffer */
 } kv_item_t;
 
-__STATIC__ kv_ctl_t kv_ctl;
+extern kv_ctl_t kv_ctl;
 
 __STATIC_INLINE__ void kv_blk_freesz_set(uint32_t blk_start, uint32_t free_size)
 {
diff --git a/components/fs/kv/tos_kv.c b/components/fs/kv/tos_kv.c
index b4de95af..2bf362e9 100644
--- a/components/fs/kv/tos_kv.c
+++ b/components/fs/kv/tos_kv.c
@@ -145,6 +145,20 @@ __STATIC__ uint32_t kv_blk_next_fresh(void)
     return KV_BLK_INVALID;
 }
 
+__STATIC__ uint32_t kv_blk_get_a_fresh(void)
+{
+    uint32_t cur_blk;
+
+    KV_BLK_FOR_EACH(cur_blk) {
+        if (kv_blk_is_fresh(cur_blk)) {
+            return cur_blk;
+        }
+    }
+
+    return KV_BLK_INVALID;
+}
+
+
 __STATIC__ uint32_t kv_blk_search_inuse(uint32_t item_size)
 {
     uint32_t cur_blk;
@@ -940,6 +954,26 @@ __STATIC__ int kv_mgr_blk_index_rebuild(void)
     return is_rebuild_done;
 }
 
+__STATIC__ kv_err_t kv_try_gc(void)
+{
+    uint32_t cur_blk, blk_dst;
+
+    blk_dst = kv_blk_get_a_fresh();
+    if (blk_dst == KV_BLK_INVALID) {
+        return KV_ERR_GC_NOTHING;
+    }
+
+    KV_BLK_FOR_EACH(cur_blk) {
+        if (kv_blk_is_dirty(cur_blk)) {
+            if (kv_do_gc(cur_blk, blk_dst, K_FALSE) == KV_ERR_NONE) {
+                return KV_ERR_NONE;
+            }
+        }
+    }
+
+    return KV_ERR_GC_NOTHING;
+}
+
 __STATIC__ kv_err_t kv_mgr_workspace_locate(void)
 {
     uint32_t cur_blk;
@@ -949,6 +983,12 @@ __STATIC__ kv_err_t kv_mgr_workspace_locate(void)
         kv_mgr_blk_index_rebuild();
     }
 
+    if (KV_MGR_BLK_NUM_INUSE == 0 && KV_MGR_BLK_NUM_FRESH == 1) {
+        /* if here, we cannot just give out the last fresh block, otherwise the kv will get into
+            KV_ERR_NO_WRITEABLE_BLK next time, try a gc here to get a "rescue" */
+        kv_try_gc();
+    }
+
     if (KV_NO_WRITEABLE_BLK()) {
         return KV_ERR_NO_WRITEABLE_BLK;
     }
@@ -1078,7 +1118,6 @@ __STATIC__ int kv_handle_incomplete_gc(struct blk_info gc_src_blk, struct blk_in
 
 __STATIC__ int kv_mgr_ctl_build(void)
 {
-    kv_err_t err;
     uint32_t cur_blk;
     kv_blk_hdr_t blk_hdr;
 
@@ -1176,22 +1215,21 @@ __STATIC__ kv_err_t kv_gc(void)
 
     // there must be at least one fresh block left, make workspace pointer to the fresh one
     blk_dst = kv_blk_next_fresh();
+    if (blk_dst == KV_BLK_INVALID) {
+        /* kinda a bug here, KV_MGR_BLK_NUM_FRESH == 1 */
+        return KV_ERR_GC_NOTHING;
+    }
 
     KV_BLK_FOR_EACH(cur_blk) {
         if (kv_blk_is_dirty(cur_blk)) {
-            if (kv_do_gc(cur_blk, blk_dst, K_FALSE) != KV_ERR_NONE) {
-                // cannot do gc for this block, give others a try
-                continue;
+            if (kv_do_gc(cur_blk, blk_dst, K_FALSE) == KV_ERR_NONE) {
+                is_gc_done = K_TRUE;
+                break;
             }
-
-            is_gc_done = K_TRUE;
-
-            break;
         }
     }
 
     if (is_gc_done) {
-        // if do nothing, should restore the workspace;
         KV_MGR_WORKSPACE = blk_dst;
     }