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From:   =?UTF-8?B?6LS65Lit5Z2k?= <hezhongkun.hzk@bytedance.com>
Date:   Thu, 15 Jun 2023 21:40:45 +0800
Message-ID: <CACSyD1NfbD_YBADH-3bR0=sGkrkEqxfgYLvyNyTiWdTvw2R6vA@mail.gmail.com>
Subject: Re: [External] Re: [RFC PATCH 1/3] zram: charge the compressed RAM to
 the page's memcgroup
To:     David Hildenbrand <david@redhat.com>
Cc:     minchan@kernel.org, senozhatsky@chromium.org, mhocko@suse.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
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> I suspect for the swap->zram we should always get charged pages, because
> we're effectively writing out charged anon/shmem pages only -- without
> any buffer in between.

Hi David=EF=BC=8Cthe charged memory will be released in swap->zram. New pag=
es
are allocated by alloc_zspage(), and we did not charge the page directly=EF=
=BC=8Cbut
the objects(like  slab), because the zspage are shared by any memcg.

>
> For the fs->zram or direct zram access device case I'm not so sure. It
> highly depends on what gets mapped into the bio (e.g., a kernel buffer,
> zeropage, ...). If it's a pagecache page, that should be charged and
> we're good. No so sure about fs metadata or some other fs cases (e.g.,
> write() to a file that bypass the pagecache).
>

Yes=EF=BC=8C the pagecaches are charged in fs->zram, but  will be released =
if
we drop the cache. the compressed objects are not charged.

> --
> Cheers,
>
> David / dhildenb
>