Do not consider blocks without deleted pages for GC

GC'ing such a block will not free any pages so is kind of pointless.
This fixes cases where GC cannot make any progress.

This also means that static data will not get rewritten and thus its
blocks not get even wear. However, since SPIFFS is not fault-tolerant
keeping static data safe and not rewriting it is a plus,
and wear-leveling takes a back seat in this case.

CL: vfs-fs-spiffs: Do not consider blocks without deleted pages for GC

PUBLISHED_FROM=984f987d715d7066273d4893222fa2ba26df029e

src/spiffs/spiffs_gc.c

@@ -315,6 +315,17 @@ s32_t spiffs_gc_find_candidate(
           used_pages_in_block * SPIFFS_GC_HEUR_W_USED +
           erase_age * (fs_crammed ? 0 : SPIFFS_GC_HEUR_W_ERASE_AGE);
       int cand_ix = 0;
+      if (deleted_pages_in_block == 0) {
+        /*
+         * GC'ing this block will not free any pages, knock it way down.
+         * This fixes cases where GC cannot make any progress.
+         * This also means that static data will not get rewritten and thus its
+         * blocks not get even wear. However, since SPIFFS is not fault-tolerant
+         * keeping static data safe and not rewriting it is a plus, and
+         * wear-leveling takes a back seat in this case.
+         */
+        score = 0;
+      }
       SPIFFS_GC_DBG("gc_check: bix:"_SPIPRIbl" del:"_SPIPRIi" use:"_SPIPRIi" score:"_SPIPRIi"\n", cur_block, deleted_pages_in_block, used_pages_in_block, score);
       while (cand_ix < max_candidates) {
         if (cand_blocks[cand_ix] == (spiffs_block_ix)-1) {