linux-kernel - Re: Re: [PATCH net-next v5 1/3] net-memcg: Fold dependency into memcg pressure cond

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Date:   Mon, 5 Jun 2023 19:52:10 +0800
From:   Abel Wu <wuyun.abel@...edance.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Simon Horman <simon.horman@...igine.com>,
        netdev@...r.kernel.org, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Re: [PATCH net-next v5 1/3] net-memcg: Fold dependency into memcg
 pressure cond

On 6/3/23 4:25 AM, Shakeel Butt wrote:
> On Fri, Jun 02, 2023 at 04:11:33PM +0800, Abel Wu wrote:
>> The callers of mem_cgroup_under_socket_pressure() should always make
>> sure that (mem_cgroup_sockets_enabled && sk->sk_memcg) is true. So
>> instead of coding around all the callsites, put the dependencies into
>> mem_cgroup_under_socket_pressure() to avoid redundancy and possibly
>> bugs.
>>
>> This change might also introduce slight function call overhead *iff*
>> the function gets expanded in the future. But for now this change
>> doesn't make binaries different (checked by vimdiff) except the one
>> net/ipv4/tcp_input.o (by scripts/bloat-o-meter), which is probably
>> negligible to performance:
>>
>> add/remove: 0/0 grow/shrink: 1/2 up/down: 5/-5 (0)
>> Function                                     old     new   delta
>> tcp_grow_window                              573     578      +5
>> tcp_try_rmem_schedule                       1083    1081      -2
>> tcp_check_space                              324     321      -3
>> Total: Before=44647, After=44647, chg +0.00%
>>
>> So folding the dependencies into mem_cgroup_under_socket_pressure()
>> is generally a good thing and provides better readablility.
>>
> 
> I don't see how it is improving readability. If you have removed the use
> of mem_cgroup_sockets_enabled completely from the networking then I can
> understand but this change IMHO will actually decrease the readability
> because the later readers will have to reason why we are doing this
> check at some places but not other.

Yes, I agree. I am trying to let networking get rid of this macro
entirely, but get stuck on inet_csk_accept().. :(