Re: [External] Re: [PATCH 0/9] Shrink the list lru size on memory cgroup removal

[Muchun Song]

On Thu, Apr 29, 2021 at 7:32 AM Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:
>
> On Wed, Apr 28, 2021 at 2:54 AM Muchun Song <songmuchun@xxxxxxxxxxxxx> 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). But now there are less than 500
> > containers in the system. And memcg_nr_cache_ids has not been reduced
> > to a suitable value. This can waste a lot of memory. If we want to reduce
> > memcg_nr_cache_ids, we have to reboot the server. This is not what we
> > want.
> >
> > So this patchset will dynamically adjust the value of memcg_nr_cache_ids
> > to keep healthy memory consumption. In this case, we may be able to restore
> > a healthy environment even if the users have created tens of thousands of
> > memory cgroups and then destroyed those memory cgroups. This patchset also
> > contains some code simplification.
> >
>
> There was a recent discussion [1] on the same issue. Did you get the
> chance to take a look at that. I have not gone through this patch
> series yet but will do in the next couple of weeks.
>
> [1] https://lore.kernel.org/linux-fsdevel/20210405054848.GA1077931@xxxxxxxxxx/

Thanks for your reminder.

No, I haven't. But now I have looked at this. The issue is very similar
to mine. But Bharata seems to want to run 10k containers. And
optimize the memory consumption of list_lru_one in this case.
This is not what I do. I want to try to shrink the size of the list lrus
when the number of memcgs is reduced from tens of thousands
to hundreds.

Thanks.