linux-kernel - [RFC][v5][PATCH 1/8]: Factor out code to allocate pidmap page

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Message-ID: <20090907211358.GA6685@us.ibm.com>
Date:	Mon, 7 Sep 2009 14:13:58 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	serue@...ibm.com, Oren Laadan <orenl@...columbia.edu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Andrew Morton <akpm@...l.org>, torvalds@...ux-foundation.org,
	mikew@...gle.com, mingo@...e.hu, hpa@...or.com,
	Containers <containers@...ts.linux-foundation.org>,
	sukadev@...ibm.com
Subject: [RFC][v5][PATCH 1/8]: Factor out code to allocate pidmap page



Subject: [RFC][v5][PATCH 1/8]: Factor out code to allocate pidmap page

To simplify alloc_pidmap(), move code to allocate a pid map page to a
separate function.

Changelog[v3]:
	- Earlier version of patchset called alloc_pidmap_page() from two
	  places. But now its called from only one place. Even so, moving
	  this code out into a separate function simplifies alloc_pidmap().
Changelog[v2]:
	- (Matt Helsley, Dave Hansen) Have alloc_pidmap_page() return
	  -ENOMEM on error instead of -1.

Signed-off-by: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Acked-by: Serge Hallyn <serue@...ibm.com>
Reviewed-by: Oren Laadan <orenl@...columbia.edu>
---
 kernel/pid.c |   46 ++++++++++++++++++++++++++++++----------------
 1 files changed, 30 insertions(+), 16 deletions(-)

Index: linux-2.6/kernel/pid.c
===================================================================
--- linux-2.6.orig/kernel/pid.c	2009-09-07 13:08:50.000000000 -0700
+++ linux-2.6/kernel/pid.c	2009-09-07 13:11:30.000000000 -0700
@@ -122,9 +122,35 @@
 	atomic_inc(&map->nr_free);
 }
 
+static int alloc_pidmap_page(struct pidmap *map)
+{
+	void *page;
+
+	if (likely(map->page))
+		return 0;
+
+	page = kzalloc(PAGE_SIZE, GFP_KERNEL);
+
+	/*
+	 * Free the page if someone raced with us installing it:
+	 */
+	spin_lock_irq(&pidmap_lock);
+	if (map->page)
+		kfree(page);
+	else
+		map->page = page;
+	spin_unlock_irq(&pidmap_lock);
+
+	if (unlikely(!map->page))
+		return -ENOMEM;
+
+	return 0;
+}
+
 static int alloc_pidmap(struct pid_namespace *pid_ns)
 {
 	int i, offset, max_scan, pid, last = pid_ns->last_pid;
+	int rc;
 	struct pidmap *map;
 
 	pid = last + 1;
@@ -134,21 +160,10 @@
 	map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
 	max_scan = (pid_max + BITS_PER_PAGE - 1)/BITS_PER_PAGE - !offset;
 	for (i = 0; i <= max_scan; ++i) {
-		if (unlikely(!map->page)) {
-			void *page = kzalloc(PAGE_SIZE, GFP_KERNEL);
-			/*
-			 * Free the page if someone raced with us
-			 * installing it:
-			 */
-			spin_lock_irq(&pidmap_lock);
-			if (map->page)
-				kfree(page);
-			else
-				map->page = page;
-			spin_unlock_irq(&pidmap_lock);
-			if (unlikely(!map->page))
-				break;
-		}
+		rc = alloc_pidmap_page(map);
+		if (rc)
+			break;
+
 		if (likely(atomic_read(&map->nr_free))) {
 			do {
 				if (!test_and_set_bit(offset, map->page)) {
--
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