[Gluster-devel] how do you debug ref leaks?

Pranith Kumar Karampuri pkarampu at redhat.com
Thu Sep 18 04:48:06 UTC 2014

On 09/18/2014 10:08 AM, Raghavendra Gowdappa wrote:
> For eg., if a dictionary is not freed because of non-zero refcount, if there is an information on who has held these references would help to narrow down the code path or component.
Yes that is the aim. The implementation I suggested tries to get that 
information per xlator. Are you saying it is better to store in the 
dict/inode/fd itself? I actually wrote one patch sometime back to do 
something similar (Not tested yet :-) ).

diff --git a/libglusterfs/src/dict.c b/libglusterfs/src/dict.c
index 37a6b2c..bd4c438 100644
--- a/libglusterfs/src/dict.c
+++ b/libglusterfs/src/dict.c
@@ -100,8 +100,10 @@ dict_new (void)

          dict = get_new_dict_full(1);

-        if (dict)
+        if (dict) {
+                dict->refs = get_new_dict_full(1);
                  dict_ref (dict);
+        }

          return dict;
@@ -446,6 +448,7 @@ dict_destroy (dict_t *this)
          data_pair_t *pair = this->members_list;
          data_pair_t *prev = this->members_list;

+        dict_destroy (this->refs);
          LOCK_DESTROY (&this->lock);

          while (prev) {
@@ -495,15 +498,21 @@ dict_unref (dict_t *this)
  dict_t *
  dict_ref (dict_t *this)
+        int32_t ref = 0;
+        xlat_t  *x = NULL;
          if (!this) {
                  gf_log_callingfn ("dict", GF_LOG_WARNING, "dict is NULL");
                  return NULL;

+        x = THIS;
          LOCK (&this->lock);


+        dict_get_in32 (this->refs, x->name, &ref);
+        dict_set_int32 (this->refs, x->name, ref+1);
          UNLOCK (&this->lock);

          return this;
@@ -513,15 +522,20 @@ void
  data_unref (data_t *this)
          int32_t ref;
+        xlator_t *x = NULL;

          if (!this) {
                  gf_log_callingfn ("dict", GF_LOG_WARNING, "dict is NULL");

+        x = THIS;
          LOCK (&this->lock);

+        dict_get_in32 (this->refs, x->name, &ref);
+        dict_set_int32 (this->refs, x->name, ref-1);
          ref = this->refcount;

          UNLOCK (&this->lock);
diff --git a/libglusterfs/src/dict.h b/libglusterfs/src/dict.h
index 682c152..33ed7bd 100644
--- a/libglusterfs/src/dict.h
+++ b/libglusterfs/src/dict.h
@@ -93,6 +93,7 @@ struct _dict {
          data_pair_t    *members_internal;
          data_pair_t     free_pair;
          gf_boolean_t    free_pair_in_use;
+        struct _dict   *refs;

I was not happy with this implementation either.

similar implementation for inode here: http://review.gluster.com/8302

But I am not happy with any of these implementations. Probably because 
it is still not granular enough, i.e. fop info is missing. It is better 
than no info but still bad. We can't have it on statedump either. So 
when User reports high memory usage we still have to spend lot of time 
looking over all the places where the dicts are allocated which is bad :-(.

> ----- Original Message -----
>> From: "Pranith Kumar Karampuri" <pkarampu at redhat.com>
>> To: "Raghavendra Gowdappa" <rgowdapp at redhat.com>
>> Cc: "Gluster Devel" <gluster-devel at gluster.org>
>> Sent: Thursday, September 18, 2014 10:05:18 AM
>> Subject: Re: [Gluster-devel] how do you debug ref leaks?
>> On 09/18/2014 09:59 AM, Raghavendra Gowdappa wrote:
>>> One thing that would be helpful is "allocator" info for generic objects
>>> like dict, inode, fd etc. That way we wouldn't have to sift through large
>>> amount of code.
>> Could you elaborate the idea please.
>> Pranith
>>> ----- Original Message -----
>>>> From: "Pranith Kumar Karampuri" <pkarampu at redhat.com>
>>>> To: "Gluster Devel" <gluster-devel at gluster.org>
>>>> Sent: Thursday, September 18, 2014 7:43:00 AM
>>>> Subject: [Gluster-devel] how do you debug ref leaks?
>>>> hi,
>>>>        Till now the only method I used to find ref leaks effectively is to
>>>> find what operation is causing ref leaks and read the code to find if
>>>> there is a ref-leak somewhere. Valgrind doesn't solve this problem
>>>> because it is reachable memory from inode-table etc. I am just wondering
>>>> if there is an effective way anyone else knows of. Do you guys think we
>>>> need a better mechanism of finding refleaks? At least which decreases
>>>> the search space significantly i.e. xlator y, fop f etc? It would be
>>>> better if we can come up with ways to integrate statedump and this infra
>>>> just like we did for mem-accounting.
>>>> One way I thought was to introduce new apis called
>>>> xl_fop_dict/inode/fd_ref/unref (). Each xl keeps an array of num_fops
>>>> per inode/dict/fd and increments/decrements accordingly. Dump this info
>>>> on statedump.
>>>> I myself am not completely sure about this idea. It requires all xlators
>>>> to change.
>>>> Any ideas?
>>>> Pranith
>>>> _______________________________________________
>>>> Gluster-devel mailing list
>>>> Gluster-devel at gluster.org
>>>> http://supercolony.gluster.org/mailman/listinfo/gluster-devel

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