linux-kernel - [PATCH 1/1] kernel/pid.c: Improve flow of a loop inside alloc

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Message-Id: <1362784067-15537-1-git-send-email-raphael.scarv@gmail.com>
Date:	Fri,  8 Mar 2013 20:07:47 -0300
From:	"Raphael S.Carvalho" <raphael.scarv@...il.com>
To:	"David S. Miller" <davem@...emloft.net>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	linux-kernel@...r.kernel.org,
	"Raphael S.Carvalho" <raphael.scarv@...il.com>
Subject: [PATCH 1/1] kernel/pid.c: Improve flow of a loop inside alloc_pidmap.

Notes: find_next_offset searches for an available "cleaned bit"
in the respective pid bitmap (page), so returns the offset if found,
otherwise it returns a value equals to BITS_PER_PAGE (invalid offset).

For example, suppose find_next_offset didn't find any available
bit, so there's no purpose to call mk_pid (Wasteful Cpu Cycles)
since it only computes a new PID based on a *valid* offset of 
the current map.

Therefore, I found it could be better to call mk_pid after
the checking (offset < BITS_PER_PAGE) returned sucessfully!

Signed-off-by: Raphael S.Carvalho <raphael.scarv@...il.com>
---
 kernel/pid.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/pid.c b/kernel/pid.c
index 047dc62..7ecb09a 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -190,8 +190,8 @@ static int alloc_pidmap(struct pid_namespace *pid_ns)
 					return pid;
 				}
 				offset = find_next_offset(map, offset);
-				pid = mk_pid(pid_ns, map, offset);
-			} while (offset < BITS_PER_PAGE && pid < pid_max);
+			} while (offset < BITS_PER_PAGE &&
+				(pid = mk_pid(pid_ns, map, offset)) < pid_max);
 		}
 		if (map < &pid_ns->pidmap[(pid_max-1)/BITS_PER_PAGE]) {
 			++map;
-- 
1.7.2.5

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