Fix bug in zero cache "current_cache_size" stats value (issue #204).

CHANGES

@@ -2,7 +2,8 @@ Version Next
 
     - Use fallocate(FALLOC_FL_PUNCH_HOLE) for empty disk cache blocks (issue #200)
     - Made sync(1) work on s3backer file to flush cached data (issue #197)
-    - Fix bug where s3b_compress=deflate NDB flag would fail (issue #195)
+    - Fixed bug where s3b_compress=deflate NDB flag would fail (issue #195)
+    - Fixed bug in zero cache "current_cache_size" stats value (issue #204)
     - Reuse cURL handles after normal HTTP error codes (issue #199)
     - Run modprobe(8) if needed when starting with the --nbd flag (issue #203)
 

s3backer.h

@@ -120,7 +120,7 @@ extern char **environ;
 typedef uint32_t    s3b_block_t;
 
 // Integral type used for bitmaps
-typedef uintptr_t   bitmap_t;
+typedef uint32_t    bitmap_t;
 
 /*
  * How many hex digits we will use to print a block number.

util.c

@@ -267,6 +267,19 @@ bitmap_or(bitmap_t *dst, const bitmap_t *src, s3b_block_t num_blocks)
         dst[i] |= src[i];
 }
 
+size_t
+bitmap_or2(bitmap_t *dst, const bitmap_t *src, s3b_block_t num_blocks)
+{
+    const size_t nwords = bitmap_size(num_blocks);
+    size_t count = 0;
+    size_t i;
+
+    assert(sizeof(bitmap_t) == 4);
+    for (i = 0; i < nwords; i++)
+        count += popcount32(dst[i] |= src[i]);
+    return count;
+}
+
 void
 bitmap_not(bitmap_t *bitmap, s3b_block_t num_blocks)
 {
@@ -277,6 +290,16 @@ bitmap_not(bitmap_t *bitmap, s3b_block_t num_blocks)
         bitmap[i] = ~bitmap[i];
 }
 
+// https://stackoverflow.com/q/109023/263801
+int
+popcount32(uint32_t value)
+{
+     value = value - ((value >> 1) & 0x55555555);
+     value = (value & 0x33333333) + ((value >> 2) & 0x33333333);
+     value = (value + (value >> 4)) & 0x0F0F0F0F;
+     return (int)((value * 0x01010101) >> 24);
+}
+
 int
 init_zero_block(u_int block_size)
 {

util.h

@@ -37,9 +37,6 @@
 // Forward decl's
 struct s3b_config;
 
-// Bitmap type
-typedef uintptr_t bitmap_t;
-
 // A list of block numbers
 struct block_list {
     s3b_block_t     *blocks;
@@ -103,6 +100,7 @@ extern int add_string(struct string_array *array, const char *fmt, ...) __attrib
 extern void free_strings(struct string_array *array);
 extern int init_zero_block(u_int block_size);
 extern void set_config_log(struct s3b_config *config, log_func_t *log);
+extern int popcount32(uint32_t value);
 
 // Versions of <err.h> that work properly even when daemonized
 extern void daemon_debug(const struct s3b_config *config, const char *fmt, ...)
@@ -130,6 +128,7 @@ extern int bitmap_test(const bitmap_t *bitmap, s3b_block_t block_num);
 extern void bitmap_set(bitmap_t *bitmap, s3b_block_t block_num, int value);
 extern void bitmap_and(bitmap_t *dst, const bitmap_t *src, s3b_block_t num_blocks);
 extern void bitmap_or(bitmap_t *dst, const bitmap_t *src, s3b_block_t num_blocks);
+extern size_t bitmap_or2(bitmap_t *dst, const bitmap_t *src, s3b_block_t num_blocks);
 extern void bitmap_not(bitmap_t *bitmap, s3b_block_t num_blocks);
 
 // Block lists

zero_cache.c

@@ -242,7 +242,7 @@ zero_cache_survey_main(void *arg)
     // Apply results (only if we completed the survey with no error)
     pthread_mutex_lock(&priv->survey_mutex);
     if (r == 0)
-        bitmap_or(priv->zeros, priv->survey_zeros, config->num_blocks);
+        priv->stats.current_cache_size = bitmap_or2(priv->zeros, priv->survey_zeros, config->num_blocks);
     survey_count = priv->survey_count;
     CHECK_RETURN(pthread_mutex_unlock(&priv->survey_mutex));