From: Andrew Morton <akpm@linux-foundation.org>
To: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
Shakeel Butt <shakeelb@google.com>, Roman Gushchin <guro@fb.com>,
Lorenzo Stoakes <lstoakes@gmail.com>,
Stephen Rothwell <sfr@canb.auug.org.au>,
Alexander Duyck <alexander.h.duyck@linux.intel.com>,
Yafang Shao <laoar.shao@gmail.com>,
Wei Yang <richard.weiyang@gmail.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/memcg: bail out early when !memcg in mem_cgroup_lruvec
Date: Fri, 27 Nov 2020 20:02:15 -0800 [thread overview]
Message-ID: <20201127200215.dc96a839cdd816361e7093e6@linux-foundation.org> (raw)
In-Reply-To: <1606446515-36069-1-git-send-email-alex.shi@linux.alibaba.com>
On Fri, 27 Nov 2020 11:08:35 +0800 Alex Shi <alex.shi@linux.alibaba.com> wrote:
> Sometime, we use NULL memcg in mem_cgroup_lruvec(memcg, pgdat)
> so we could get out early in the situation to avoid useless checking.
>
> Also warning if both parameter are NULL.
Why do you think a warning is needed here?
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -613,14 +613,13 @@ static inline struct lruvec *mem_cgroup_lruvec(struct mem_cgroup *memcg,
> struct mem_cgroup_per_node *mz;
> struct lruvec *lruvec;
>
> - if (mem_cgroup_disabled()) {
> + VM_WARN_ON_ONCE(!memcg && !pgdat);
> +
> + if (mem_cgroup_disabled() || !memcg) {
> lruvec = &pgdat->__lruvec;
> goto out;
> }
>
> - if (!memcg)
> - memcg = root_mem_cgroup;
> -
This change isn't obviously equivalent, is it?
> mz = mem_cgroup_nodeinfo(memcg, pgdat->node_id);
> lruvec = &mz->lruvec;
> out:
And the resulting code is awkward:
if (mem_cgroup_disabled() || !memcg) {
lruvec = &pgdat->__lruvec;
goto out;
}
mz = mem_cgroup_nodeinfo(memcg, pgdat->node_id);
lruvec = &mz->lruvec;
out:
could be
if (mem_cgroup_disabled() || !memcg) {
lruvec = &pgdat->__lruvec;
} else {
mem_cgroup_per_node mz;
mz = mem_cgroup_nodeinfo(memcg, pgdat->node_id);
lruvec = &mz->lruvec;
}
next prev parent reply other threads:[~2020-11-28 4:31 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-27 3:08 [PATCH] mm/memcg: bail out early when !memcg in mem_cgroup_lruvec Alex Shi
2020-11-28 4:02 ` Andrew Morton [this message]
2020-11-29 4:43 ` Alex Shi
2020-11-30 19:44 ` Dmitry Osipenko
2020-11-30 20:19 ` Andrew Morton
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