Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20230615034830.1361853-1-hezhongkun.hzk@bytedance.com>
 <d9b22eaa-00a1-6c5c-99a0-126b085f7cb0@redhat.com> <CACSyD1NxcYn_Uy2DUk1ywSyWsxFzq4H+poaWvF55SZZz5W-uRw@mail.gmail.com>
 <3f54542e-235b-8456-f13f-786d21c6c14f@redhat.com> <CACSyD1OxAMowHTE7KnL8nac_-=Vp4eyO00oyMLFo0qcEHx33GA@mail.gmail.com>
 <bd119703-7b7b-c4ab-0c38-9b85809de252@redhat.com> <CACSyD1NfbD_YBADH-3bR0=sGkrkEqxfgYLvyNyTiWdTvw2R6vA@mail.gmail.com>
 <290d79bb-b1a6-3146-76a7-9938829e6ebe@redhat.com>
In-Reply-To: <290d79bb-b1a6-3146-76a7-9938829e6ebe@redhat.com>
From:   =?UTF-8?B?6LS65Lit5Z2k?= <hezhongkun.hzk@bytedance.com>
Date:   Fri, 16 Jun 2023 11:44:01 +0800
Message-ID: <CACSyD1OK9=AuB8OWgk0WQwXc_tf827CMMor_qNs4VGUEM_suLA@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,
        Matthew Wilcox <willy@infradead.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

>
> Yes. But just to stress again, one issue I see is that if there is a
> page in the BIO that is not charged, you cannot charge the compressed pag=
e.

I got it. Thanks.

>
> Assume you have some FS on that zram block device and  you want to make
> sure it gets properly charged to whoever is reading/writing a file on
> that filesystem. (imagine something like a compress shmem)
>
> If a user (or the filesystem?) can trigger a BIO that has an uncharged
> page in it, it would not get charged accordingly.
>
> The "easy" reproducer would have been O_DIRECT write() using the shared
> zeropage, but zram_write_page() is smart enough to optimize for that
> case (page_same_filled()). :)

Ok, I will try it.

>
> Maybe I'm over-thinking this (well, the we do have partial I/O support,
> so something seems to be able to trigger such cases), and it would be
> great if someone with more FS->BIO experience could comment.
>
> I'll note that this is fundamentally different to zswap, because with
> zswap you don't get arbitrary BIOs, you get an anon or shmem page (that
> should be charged).
>

Hi David=EF=BC=8C I know your concern and I will try to find the uncharged =
case.

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