Children creating AOF or RDB files now report memory used by COW.

Finally Redis is able to report the amount of memory used by
copy-on-write while saving an RDB or writing an AOF file in background.

Note that this information is currently only logged (at NOTICE level)
and not shown in INFO because this is less trivial (but surely doable
with some minor form of interprocess communication).

The reason we can't capture this information on the parent before we
call wait3() is that the Linux kernel will release the child memory
ASAP, and only retain the minimal state for the process that is useful
to report the child termination to the parent.

The COW size is obtained by summing all the Private_Dirty fields found
in the "smap" file inside the proc filesystem for the process.

All this is Linux specific and is not available on other systems.

diff --git a/src/aof.c b/src/aof.c
index bc92cdb98b9c3a5b897bd07f808cd68098635989..6289e4dd5bd7d58d64d977da86b16878d0de63c7 100644 (file)
--- a/src/aof.c
+++ b/src/aof.c
@@ -962,6 +962,13 @@ int rewriteAppendOnlyFileBackground(void) {
         if (server.sofd > 0) close(server.sofd);
         snprintf(tmpfile,256,"temp-rewriteaof-bg-%d.aof", (int) getpid());
         if (rewriteAppendOnlyFile(tmpfile) == REDIS_OK) {
+            size_t private_dirty = zmalloc_get_private_dirty();
+
+            if (private_dirty) {
+                redisLog(REDIS_NOTICE,
+                    "AOF rewrite: %lu MB of memory used by copy-on-write",
+                    private_dirty/(1024*1024));
+            }
             exitFromChild(0);
         } else {
             exitFromChild(1);

diff --git a/src/rdb.c b/src/rdb.c
index a57b72e43daffc83c8bcbe41155a43f425a5b524..3d5ac2043a20603e35bff26fbb0aafbcb5ecfe9c 100644 (file)
--- a/src/rdb.c
+++ b/src/rdb.c
@@ -731,6 +731,15 @@ int rdbSaveBackground(char *filename) {
         if (server.ipfd > 0) close(server.ipfd);
         if (server.sofd > 0) close(server.sofd);
         retval = rdbSave(filename);
+        if (retval == REDIS_OK) {
+            size_t private_dirty = zmalloc_get_private_dirty();
+
+            if (private_dirty) {
+                redisLog(REDIS_NOTICE,
+                    "RDB: %lu MB of memory used by copy-on-write",
+                    private_dirty/(1024*1024));
+            }
+        }
         exitFromChild((retval == REDIS_OK) ? 0 : 1);
     } else {
         /* Parent */