linux-kernel - [PATCH mm-unstable v1 4/4] mm: clean up mem_cgroup

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Message-ID: <20240724190214.1108049-5-kinseyho@google.com>
Date: Wed, 24 Jul 2024 19:02:14 +0000
From: Kinsey Ho <kinseyho@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	Yosry Ahmed <yosryahmed@...gle.com>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Kinsey Ho <kinseyho@...gle.com>
Subject: [PATCH mm-unstable v1 4/4] mm: clean up mem_cgroup_iter()

A clean up to make variable names more clear and to improve code
readability.

No functional change.

Signed-off-by: Kinsey Ho <kinseyho@...gle.com>
---
 mm/memcontrol.c | 36 ++++++++++++++----------------------
 1 file changed, 14 insertions(+), 22 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 4314a2b8848d..7e3e95c62122 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -992,9 +992,9 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
 				   struct mem_cgroup_reclaim_cookie *reclaim)
 {
 	struct mem_cgroup_reclaim_iter *iter;
-	struct cgroup_subsys_state *css = NULL;
-	struct mem_cgroup *memcg = NULL;
-	struct mem_cgroup *pos = NULL;
+	struct cgroup_subsys_state *css;
+	struct mem_cgroup *pos;
+	struct mem_cgroup *next = NULL;
 
 	if (mem_cgroup_disabled())
 		return NULL;
@@ -1006,10 +1006,9 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
 restart:
 	if (reclaim) {
 		int gen;
-		struct mem_cgroup_per_node *mz;
+		int nid = reclaim->pgdat->node_id;
 
-		mz = root->nodeinfo[reclaim->pgdat->node_id];
-		iter = &mz->iter;
+		iter = &root->nodeinfo[nid]->iter;
 		gen = atomic_read(&iter->generation);
 
 		/*
@@ -1022,43 +1021,36 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
 			goto out_unlock;
 
 		pos = rcu_dereference(iter->position);
-	} else if (prev) {
+	} else
 		pos = prev;
-	}
 
-	if (pos)
-		css = &pos->css;
-
-	for (;;) {
-		css = css_next_descendant_pre(css, &root->css);
-		if (!css) {
-			break;
-		}
+	css = pos ? &pos->css : NULL;
 
+	while ((css = css_next_descendant_pre(css, &root->css))) {
 		/*
 		 * Verify the css and acquire a reference.  The root
 		 * is provided by the caller, so we know it's alive
 		 * and kicking, and don't take an extra reference.
 		 */
-		if (css == &root->css || css_tryget(css)) {
-			memcg = mem_cgroup_from_css(css);
+		if (css == &root->css || css_tryget(css))
 			break;
-		}
 	}
 
+	next = mem_cgroup_from_css(css);
+
 	if (reclaim) {
 		/*
 		 * The position could have already been updated by a competing
 		 * thread, so check that the value hasn't changed since we read
 		 * it to avoid reclaiming from the same cgroup twice.
 		 */
-		if (cmpxchg(&iter->position, pos, memcg) != pos) {
+		if (cmpxchg(&iter->position, pos, next) != pos) {
 			if (css && css != &root->css)
 				css_put(css);
 			goto restart;
 		}
 
-		if (!memcg) {
+		if (!next) {
 			atomic_inc(&iter->generation);
 
 			/*
@@ -1077,7 +1069,7 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
 	if (prev && prev != root)
 		css_put(&prev->css);
 
-	return memcg;
+	return next;
 }
 
 /**
-- 
2.45.2.1089.g2a221341d9-goog