Re: [PATCH v3 00/76] Optimize list lru memory consumption

[Muchun Song <songmuchun@bytedance.com>]

On Sat, Sep 18, 2021 at 2:56 PM Kari Argillander
<kari.argillander@gmail.com> wrote:
>
> On Tue, Sep 14, 2021 at 03:28:22PM +0800, Muchun Song wrote:
> > We introduced alloc_inode_sb() in previous version 2, which sets up the
> > inode reclaim context properly, to allocate filesystems specific inode.
> > So we have to convert to new API for all filesystems, which is done in
> > one patch. Some filesystems are easy to convert (just replace
> > kmem_cache_alloc() to alloc_inode_sb()), while other filesystems need to
> > do more work. In order to make it easy for maintainers of different
> > filesystems to review their own maintained part, I split the patch into
> > patches which are per-filesystem in this version. I am not sure if this
> > is a good idea, because there is going to be more commits.
> >
> > 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 now the number of memory cgroups is less than 500. So I
> > guess more than 12286 memory cgroups have been created on this machine (I
> > do not know why there are so many cgroups, it may be a user's bug or
> > the user really want to do that). Because memcg_nr_cache_ids has not been
> > reduced to a suitable value. It leads to 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.
> >
> > In order to reduce memcg_nr_cache_ids, I had posted a patchset [1] to do
> > this. But this did not fundamentally solve the problem.
> >
> > We currently allocate scope for every memcg to be able to tracked on every
> > superblock instantiated in the system, regardless of whether that superblock
> > is even accessible to that memcg.
> >
> > These huge memcg counts come from container hosts where memcgs are confined
> > to just a small subset of the total number of superblocks that instantiated
> > at any given point in time.
> >
> > For these systems with huge container counts, list_lru does not need the
> > capability of tracking every memcg on every superblock.
> >
> > What it comes down to is that the list_lru is only needed for a given memcg
> > if that memcg is instatiating and freeing objects on a given list_lru.
> >
> > As Dave said, "Which makes me think we should be moving more towards 'add the
> > memcg to the list_lru at the first insert' model rather than 'instantiate
> > all at memcg init time just in case'."
> >
> > This patchset aims to optimize the list lru memory consumption from different
> > aspects.
> >
> > Patch 1-6 are code simplification.
> > Patch 7 converts the array from per-memcg per-node to per-memcg
> > Patch 8 introduces kmem_cache_alloc_lru()
> > Patch 9 introduces alloc_inode_sb()
> > Patch 10-66 convert all filesystems to alloc_inode_sb() respectively.
>
> There is now days also ntfs3. If you do not plan to convert this please
> CC me atleast so that I can do it when these lands.
>
>   Argillander
>

Wow, a new filesystem. I didn't notice it before. I'll cover it
in the next version and Cc you if you can do a review.
Thanks for your reminder.