linux-kernel - [PATCH v1 5/5] kvfree_rcu: Fix comments according to current code

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Date:   Wed, 28 Apr 2021 15:44:22 +0200
From:   "Uladzislau Rezki (Sony)" <urezki@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>, RCU <rcu@...r.kernel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>
Cc:     Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Axtens <dja@...ens.net>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Uladzislau Rezki <urezki@...il.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: [PATCH v1 5/5] kvfree_rcu: Fix comments according to current code

We used to have an "emergency path" and comments related
to it. According to current kvfree_rcu() design that path
is not considered as emergency anymore.

This patch rephrases and updates comments regarding this.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
---
 kernel/rcu/tree.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 229e909ad437..91b978e90c3b 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3332,9 +3332,11 @@ static void kfree_rcu_work(struct work_struct *work)
 	}
 
 	/*
-	 * Emergency case only. It can happen under low memory
-	 * condition when an allocation gets failed, so the "bulk"
-	 * path can not be temporary maintained.
+	 * This is used when the "bulk" path can not be temporary
+	 * maintained for the double-argument of kvfree_rcu(). It
+	 * happens because a page-cache is empty, thus objects are
+	 * queued to the linked-list instead. This path is named
+	 * as "Channel 3".
 	 */
 	for (; head; head = next) {
 		unsigned long offset = (unsigned long)head->func;
@@ -3380,8 +3382,8 @@ static inline bool queue_kfree_rcu_work(struct kfree_rcu_cpu *krcp)
 		if ((krcp->bkvhead[0] && !krwp->bkvhead_free[0]) ||
 			(krcp->bkvhead[1] && !krwp->bkvhead_free[1]) ||
 				(krcp->head && !krwp->head_free)) {
-			// Channel 1 corresponds to SLAB ptrs.
-			// Channel 2 corresponds to vmalloc ptrs.
+			// Channel 1 corresponds to SLAB ptrs. bulk path.
+			// Channel 2 corresponds to vmalloc ptrs. bulk path.
 			for (j = 0; j < FREE_N_CHANNELS; j++) {
 				if (!krwp->bkvhead_free[j]) {
 					krwp->bkvhead_free[j] = krcp->bkvhead[j];
@@ -3389,7 +3391,8 @@ static inline bool queue_kfree_rcu_work(struct kfree_rcu_cpu *krcp)
 				}
 			}
 
-			// Channel 3 corresponds to emergency path.
+			// Channel 3 corresponds to objects queued to the
+			// linked-list for both SLAB and vmalloc pointers.
 			if (!krwp->head_free) {
 				krwp->head_free = krcp->head;
 				krcp->head = NULL;
-- 
2.20.1