On Mon, Dec 20, 2021 at 04:56:43PM +0800, Muchun Song wrote: > In our server, we found a suspected memory leak problem. The kmalloc-32 > consumes more than 6GB of memory. Other kmem_caches consume less than > 2GB memory. > > After our in-depth analysis, the memory consumption of kmalloc-32 slab > cache is the cause of list_lru_one allocation. > > crash> p memcg_nr_cache_ids > memcg_nr_cache_ids = $2 = 24574 > > memcg_nr_cache_ids is very large and memory consumption of each list_lru > can be calculated with the following formula. > > num_numa_node * memcg_nr_cache_ids * 32 (kmalloc-32) > > There are 4 numa nodes in our system, so each list_lru consumes ~3MB. > > crash> list super_blocks | wc -l > 952 > > Every mount will register 2 list lrus, one is for inode, another is for > dentry. There are 952 super_blocks. So the total memory is 952 * 2 * 3 > MB (~5.6GB). But the number of memory cgroup is less than 500. So I > guess more than 12286 containers have been deployed on this machine (I > do not know why there are so many containers, it may be a user's bug or > the user really want to do that). And memcg_nr_cache_ids has not been > reduced to a suitable value. This can waste a lot of memory. But on the other side you increase the size of struct list_lru_per_memcg, so if number of cgroups is close to memcg_nr_cache_ids, we can actually waste more memory. I'm not saying the change is not worth it, but would be nice to add some real-world numbers. Or it's all irrelevant and is done as a preparation to the conversion to xarray? If so, please, make it clear. Thanks!
