在 2020/11/28 下午12:02, Andrew Morton 写道:
> On Fri, 27 Nov 2020 11:08:35 +0800 Alex Shi <alex....@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?
Uh, Consider there are no problem for long time, it could be saved.
>
>> --- 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?
If !memcg, the root_mem_cgroup will still lead the lruvec to a pgdat
same as parameter.
>
>> 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;
> }
>
Right. remove 'goto' is better for understander.
So, is the following patch ok?
>From 225f29e03b40a7cbaeb4e3bb76f8efbcd7d648a2 Mon Sep 17 00:00:00 2001
From: Alex Shi <alex....@linux.alibaba.com>
Date: Wed, 25 Nov 2020 14:06:33 +0800
Subject: [PATCH v2] mm/memcg: bail out early when !memcg in mem_cgroup_lruvec
Sometime, we use NULL memcg in mem_cgroup_lruvec(memcg, pgdat)
so we could get out early in the situation to avoid useless checking.
Polished as Andrew Morton's suggestion.
Signed-off-by: Alex Shi <alex....@linux.alibaba.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Johannes Weiner <han...@cmpxchg.org>
Cc: Shakeel Butt <shake...@google.com>
Cc: Roman Gushchin <g...@fb.com>
Cc: Lorenzo Stoakes <lstoa...@gmail.com>
Cc: Stephen Rothwell <s...@canb.auug.org.au>
Cc: Alexander Duyck <alexander.h.du...@linux.intel.com>
Cc: Yafang Shao <laoar.s...@gmail.com>
Cc: Wei Yang <richard.weiy...@gmail.com>
Cc: linux-kernel@vger.kernel.org
---
include/linux/memcontrol.h | 15 ++++++---------
1 file changed, 6 insertions(+), 9 deletions(-)
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 3e6a1df3bdb9..4ff2ffe2b73d 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -610,20 +610,17 @@ mem_cgroup_nodeinfo(struct mem_cgroup *memcg, int nid)
static inline struct lruvec *mem_cgroup_lruvec(struct mem_cgroup *memcg,
struct pglist_data *pgdat)
{
- struct mem_cgroup_per_node *mz;
struct lruvec *lruvec;
- if (mem_cgroup_disabled()) {
+ if (mem_cgroup_disabled() || !memcg) {
lruvec = &pgdat->__lruvec;
- goto out;
- }
+ } else {
+ struct mem_cgroup_per_node *mz;
- if (!memcg)
- memcg = root_mem_cgroup;
+ mz = mem_cgroup_nodeinfo(memcg, pgdat->node_id);
+ lruvec = &mz->lruvec;
+ }
- mz = mem_cgroup_nodeinfo(memcg, pgdat->node_id);
- lruvec = &mz->lruvec;
-out:
/*
* Since a node can be onlined after the mem_cgroup was created,
* we have to be prepared to initialize lruvec->pgdat here;
--
2.29.GIT
