linux-kernel - [PATCH v8 2/6] memcontrol: implement mem_cgroup_tryget

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Message-Id: <20231130194023.4102148-3-nphamcs@gmail.com>
Date:   Thu, 30 Nov 2023 11:40:19 -0800
From:   Nhat Pham <nphamcs@...il.com>
To:     akpm@...ux-foundation.org
Cc:     hannes@...xchg.org, cerasuolodomenico@...il.com,
        yosryahmed@...gle.com, sjenning@...hat.com, ddstreet@...e.org,
        vitaly.wool@...sulko.com, mhocko@...nel.org,
        roman.gushchin@...ux.dev, shakeelb@...gle.com,
        muchun.song@...ux.dev, chrisl@...nel.org, linux-mm@...ck.org,
        kernel-team@...a.com, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kselftest@...r.kernel.org, shuah@...nel.org
Subject: [PATCH v8 2/6] memcontrol: implement mem_cgroup_tryget_online()

This patch implements a helper function that try to get a reference to
an memcg's css, as well as checking if it is online. This new function
is almost exactly the same as the existing mem_cgroup_tryget(), except
for the onlineness check. In the !CONFIG_MEMCG case, it always returns
true, analogous to mem_cgroup_tryget(). This is useful for e.g to the
new zswap writeback scheme, where we need to select the next online
memcg as a candidate for the global limit reclaim.

Signed-off-by: Nhat Pham <nphamcs@...il.com>
---
 include/linux/memcontrol.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 7bdcf3020d7a..2bd7d14ace78 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -821,6 +821,11 @@ static inline bool mem_cgroup_tryget(struct mem_cgroup *memcg)
 	return !memcg || css_tryget(&memcg->css);
 }
 
+static inline bool mem_cgroup_tryget_online(struct mem_cgroup *memcg)
+{
+	return !memcg || css_tryget_online(&memcg->css);
+}
+
 static inline void mem_cgroup_put(struct mem_cgroup *memcg)
 {
 	if (memcg)
@@ -1349,6 +1354,11 @@ static inline bool mem_cgroup_tryget(struct mem_cgroup *memcg)
 	return true;
 }
 
+static inline bool mem_cgroup_tryget_online(struct mem_cgroup *memcg)
+{
+	return true;
+}
+
 static inline void mem_cgroup_put(struct mem_cgroup *memcg)
 {
 }
-- 
2.34.1