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Date:   Sat, 1 May 2021 04:27:49 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Muchun Song <songmuchun@bytedance.com>
Cc:     Dave Chinner <david@fromorbit.com>, Roman Gushchin <guro@fb.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Shakeel Butt <shakeelb@google.com>,
        Yang Shi <shy828301@gmail.com>, alexs@kernel.org,
        Alexander Duyck <alexander.h.duyck@linux.intel.com>,
        Wei Yang <richard.weiyang@gmail.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux Memory Management List <linux-mm@kvack.org>
Subject: Re: [External] Re: [PATCH 0/9] Shrink the list lru size on memory
 cgroup removal
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On Fri, Apr 30, 2021 at 04:32:39PM +0800, Muchun Song wrote:
> Before start, we should know about the following rules of list lrus.
> 
> - Only objects allocated with __GFP_ACCOUNT need to allocate
>   the struct list_lru_node.
> - The caller of allocating memory must know which list_lru the
>   object will insert.
> 
> So we can allocate struct list_lru_node when allocating the
> object instead of allocating it when list_lru_add().  It is easy, because
> we already know the list_lru and memcg which the object belongs
> to. So we can introduce a new helper to allocate the object and
> list_lru_node. Like below.

I feel like there may be a simpler solution, although I'm not really
familiar with the list_lru situation.  The three caches you mention:

> I have looked at the code closely. There are 3 different kmem_caches that
> need to use this new API to allocate memory. They are inode_cachep,
> dentry_cache and radix_tree_node_cachep. I think that it is easy to migrate.

are all filesystem.  So if there's a way of knowing which filesystems
are exposed to each container, we can allocate the list_lru structures at
"mount" time rather than at first allocation for a given cache/lru/memcg
combination.