linux-kernel - Re: [External] Re: [RFC PATCH 1/3] zram: charge the compressed RAM to the page's memcgroup

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Date:   Thu, 15 Jun 2023 19:15:41 +0800
From:   贺中坤 <hezhongkun.hzk@...edance.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     minchan@...nel.org, senozhatsky@...omium.org, mhocko@...e.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [RFC PATCH 1/3] zram: charge the compressed RAM to
 the page's memcgroup

On Thu, Jun 15, 2023 at 5:27 PM David Hildenbrand <david@...hat.com> wrote:
>
> Interesting. When looking at possible ways to achieve that in a clean
> way, my understanding was that the page might not always be accounted to
> a memcg (e.g., simply some buffer?). Besides the swap->zram case I was
> thinking about other fs->zram case, or just a straight read/write to the
> zram device.
>
> The easiest way to see where that goes wrong I think is
> zram_bvec_write_partial(), where we simply allocate a temporary page.
>
> Either I am missing something important, or this only works in some
> special cases.
>
> I came to the conclusion that the only reasonable way is to assign a
> complete zram device to a single cgroup and have all memory accounted to
> that cgroup. Does also not solve all use cases (especially the
> swap->zram case that might be better offjust using zswap?) but at least
> the memory gets accounted in a more predictable way.
>
> Happy to learn more.
>
> --
> Cheers,
>
> David / dhildenb
>

Hi david, thanks for your reply. This should be my mistake, I didn't
describe the
problem clearly.

The reason for the problem is not the temporary page allocated at the beginning
of zram_bvec_write_partial() and released at the end,but the compressed memory
allocated by zs_malloc() in zram_write_page().

So, it may not meet the need to  assign a complete zram device to a
single cgroup.
we need to charge the compressed memory to the original page's memory cgroup,
which is not charged so far.