linux-kernel - Re: [PATCH 1/8] cgroups: add res_counter_write

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Date:	Mon, 16 Jan 2012 14:27:13 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Li Zefan <lizf@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Aditya Kali <adityakali@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Kay Sievers <kay.sievers@...y.org>,
	Tim Hockin <thockin@...kin.org>, Tejun Heo <htejun@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/8] cgroups: add res_counter_write_u64() API

On Fri, Jan 13, 2012 at 07:13:47PM +0100, Frederic Weisbecker wrote:
> Extend the resource counter API with a mirror of res_counter_read_u64() to
> make it handy to update a resource counter value from a cgroup subsystem
> u64 value file.

I still think it worth to have two versions of res_counter_write_u64().
>From my POV, it's clean enough, but consistent with res_counter_read_u64()
and faster on 64bit system.

What do you think?

---
diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
index c9d625c..1b3fe05 100644
--- a/include/linux/res_counter.h
+++ b/include/linux/res_counter.h
@@ -82,6 +82,8 @@ int res_counter_memparse_write_strategy(const char *buf,
 int res_counter_write(struct res_counter *counter, int member,
 		      const char *buffer, write_strategy_fn write_strategy);
 
+void res_counter_write_u64(struct res_counter *counter, int member, u64 val);
+
 /*
  * the field descriptors. one for each member of res_counter
  */
diff --git a/kernel/res_counter.c b/kernel/res_counter.c
index 6d269cc..aad4ddb 100644
--- a/kernel/res_counter.c
+++ b/kernel/res_counter.c
@@ -167,12 +167,27 @@ int res_counter_memparse_write_strategy(const char *buf,
 	return 0;
 }
 
+#if BITS_PER_LONG == 32
+void res_counter_write_u64(struct res_counter *counter, int member, u64 val)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&counter->lock, flags);
+	*res_counter_member(counter, member) = val;
+	spin_unlock_irqrestore(&counter->lock, flags);
+}
+#else
+void res_counter_write_u64(struct res_counter *counter, int member, u64 val)
+{
+	*res_counter_member(counter, member) = val;
+}
+#endif
+
 int res_counter_write(struct res_counter *counter, int member,
 		      const char *buf, write_strategy_fn write_strategy)
 {
 	char *end;
-	unsigned long flags;
-	unsigned long long tmp, *val;
+	unsigned long long tmp;
 
 	if (write_strategy) {
 		if (write_strategy(buf, &tmp))
@@ -182,9 +197,8 @@ int res_counter_write(struct res_counter *counter, int member,
 		if (*end != '\0')
 			return -EINVAL;
 	}
-	spin_lock_irqsave(&counter->lock, flags);
-	val = res_counter_member(counter, member);
-	*val = tmp;
-	spin_unlock_irqrestore(&counter->lock, flags);
+
+	res_counter_write_u64(counter, member, tmp);
+
 	return 0;
 }
-- 
 Kirill A. Shutemov
--
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