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

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Message-ID: <CACSyD1Pz0SHOZ-aMr6NQ7vX5iNuhUUEnH=iysR49uxo=mbfN=Q@mail.gmail.com>
Date:   Thu, 15 Jun 2023 19:58:37 +0800
From:   贺中坤 <hezhongkun.hzk@...edance.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     minchan@...nel.org, senozhatsky@...omium.org, 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

Hi michal,  glad to hear from you.

> I am not really deeply familiar with zram implementation nor usage but
> how is the above allocation going to be charged without __GFP_ACCOUNT in
> the gfp mask?

Yes，zs_malloc() did not charge compressed memory, even if we add this gfp.
so we need to implement this function in this patchset. But this flag should be
used to enable this feature.

> Also what exactly is going to happen for the swap backed by the zram
> device? Your memcg might be hitting the hard limit and therefore
> swapping out. Wouldn't zs_malloc fail very likely under that condition
> making the swap effectively unusable?

This is the key point, as i said above, zs_malloc() did not charge
compressed memory,
so zs_malloc will not fail under that condition. if the zram swap is
large enough, zs_malloc
never fails unless system OOM.   so memory.max will be invalidated.

> --
> Michal Hocko
> SUSE Labs