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

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Date:   Wed, 28 Apr 2021 16:32:07 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Roman Gushchin <guro@...com>, Yang Shi <shy828301@...il.com>,
        alexs@...nel.org,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Wei Yang <richard.weiyang@...il.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>
Subject: Re: [PATCH 0/9] Shrink the list lru size on memory cgroup removal

On Wed, Apr 28, 2021 at 2:54 AM Muchun Song <songmuchun@...edance.com> 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@in.ibm.com/