zmalloc: zmalloc_get_smap_bytes_by_field() modified to work for any PID.

The goal is to get copy-on-write amount of the child from the parent.

src/aof.c

@@ -1328,7 +1328,7 @@ int rewriteAppendOnlyFileBackground(void) {
         redisSetProcTitle("redis-aof-rewrite");
         snprintf(tmpfile,256,"temp-rewriteaof-bg-%d.aof", (int) getpid());
         if (rewriteAppendOnlyFile(tmpfile) == C_OK) {
-            size_t private_dirty = zmalloc_get_private_dirty();
+            size_t private_dirty = zmalloc_get_private_dirty(-1);
 
             if (private_dirty) {
                 serverLog(LL_NOTICE,

src/latency.c

@@ -79,7 +79,7 @@ int THPIsEnabled(void) {
  * value of the function is non-zero, the process is being targeted by
  * THP support, and is likely to have memory usage / latency issues. */
 int THPGetAnonHugePagesSize(void) {
-    return zmalloc_get_smap_bytes_by_field("AnonHugePages:");
+    return zmalloc_get_smap_bytes_by_field("AnonHugePages:",-1);
 }
 
 /* ---------------------------- Latency API --------------------------------- */

src/rdb.c

@@ -1024,7 +1024,7 @@ int rdbSaveBackground(char *filename) {
         redisSetProcTitle("redis-rdb-bgsave");
         retval = rdbSave(filename);
         if (retval == C_OK) {
-            size_t private_dirty = zmalloc_get_private_dirty();
+            size_t private_dirty = zmalloc_get_private_dirty(-1);
 
             if (private_dirty) {
                 serverLog(LL_NOTICE,
@@ -1761,7 +1761,7 @@ int rdbSaveToSlavesSockets(void) {
             retval = C_ERR;
 
         if (retval == C_OK) {
-            size_t private_dirty = zmalloc_get_private_dirty();
+            size_t private_dirty = zmalloc_get_private_dirty(-1);
 
             if (private_dirty) {
                 serverLog(LL_NOTICE,

src/zmalloc.c

@@ -304,15 +304,26 @@ float zmalloc_get_fragmentation_ratio(size_t rss) {
  * /proc/self/smaps. The field must be specified with trailing ":" as it
  * apperas in the smaps output.
  *
- * Example: zmalloc_get_smap_bytes_by_field("Rss:");
+ * If a pid is specified, the information is extracted for such a pid,
+ * otherwise if pid is -1 the information is reported is about the
+ * current process.
+ *
+ * Example: zmalloc_get_smap_bytes_by_field("Rss:",-1);
  */
 #if defined(HAVE_PROC_SMAPS)
-size_t zmalloc_get_smap_bytes_by_field(char *field) {
+size_t zmalloc_get_smap_bytes_by_field(char *field, long pid) {
     char line[1024];
     size_t bytes = 0;
-    FILE *fp = fopen("/proc/self/smaps","r");
     int flen = strlen(field);
 
+    if (pid == -1) {
+        FILE *fp = fopen("/proc/self/smaps","r");
+    } else {
+        char filename[128];
+        snprintf(filename,sizeof(filename),"/proc/%ld/smaps",pid);
+        FILE *fp = fopen(filename,"r");
+    }
+
     if (!fp) return 0;
     while(fgets(line,sizeof(line),fp) != NULL) {
         if (strncmp(line,field,flen) == 0) {
@@ -327,14 +338,15 @@ size_t zmalloc_get_smap_bytes_by_field(char *field) {
     return bytes;
 }
 #else
-size_t zmalloc_get_smap_bytes_by_field(char *field) {
+size_t zmalloc_get_smap_bytes_by_field(char *field, long pid) {
     ((void) field);
+    ((void) pid);
     return 0;
 }
 #endif
 
-size_t zmalloc_get_private_dirty(void) {
-    return zmalloc_get_smap_bytes_by_field("Private_Dirty:");
+size_t zmalloc_get_private_dirty(long pid) {
+    return zmalloc_get_smap_bytes_by_field("Private_Dirty:",pid);
 }
 
 /* Returns the size of physical memory (RAM) in bytes.

src/zmalloc.h

@@ -75,8 +75,8 @@ void zmalloc_enable_thread_safeness(void);
 void zmalloc_set_oom_handler(void (*oom_handler)(size_t));
 float zmalloc_get_fragmentation_ratio(size_t rss);
 size_t zmalloc_get_rss(void);
-size_t zmalloc_get_private_dirty(void);
-size_t zmalloc_get_smap_bytes_by_field(char *field);
+size_t zmalloc_get_private_dirty(long pid);
+size_t zmalloc_get_smap_bytes_by_field(char *field, long pid);
 size_t zmalloc_get_memory_size(void);
 void zlibc_free(void *ptr);