[PATCHES BUG 13865] memcache tracking of talloc object sizes

[Jeremy Allison]

On Thu, Mar 28, 2019 at 11:28:47AM -0700, Christof Schmitt via samba-technical wrote:
> On Thu, Mar 28, 2019 at 11:28:14AM -0700, Christof Schmitt wrote:
> > This is a fix for memcache to also add the talloc object size to the
> > amount of used space. The objects become part of the memcache, so the
> > sizes should be tracked as well.
> > 
> > The third patch is a clarification to the description of the 'max stat
> > cache size' parameter.
> > 
> > Pipeline is running at:
> > https://gitlab.com/samba-team/devel/samba/pipelines/54120627
> > 
> > Christof
> 
> And here are the actual patches.

Not quite complete I think. In the original memcache_add()
code we have a corner case where a talloc'ed key value is
being replaced with a non-talloc'ed value (yeah I know,
goes into the "don't do that catagory" but we currently
cope with it :-).

The code goes:

271         e = memcache_find(cache, n, key);
272 
273         if (e != NULL) {
274                 memcache_element_parse(e, &cache_key, &cache_value);
275 
276                 if (value.length <= cache_value.length) {
277                         if (memcache_is_talloc(e->n)) {
278                                 void *ptr;
279                                 SMB_ASSERT(cache_value.length == sizeof(ptr));
280                                 memcpy(&ptr, cache_value.data, sizeof(ptr));

I think you need to add:

+				    cache->size -= talloc_total_size(ptr);

here to keep the size consistent in this edge case.

281                                 TALLOC_FREE(ptr);
282                         }
283                         /*
284                          * We can reuse the existing record
285                          */
286                         memcpy(cache_value.data, value.data, value.length);
287                         e->valuelength = value.length;
288                         return;
289                 }

Probably need to add a test for this too...

Jeremy.