From: Miklos Szeredi <miklos@szeredi.hu>
Date: Fri, 23 Jun 2006 09:05:10 +0000 (-0700)
Subject: [PATCH] locks: don't do unnecessary allocations
X-Git-Tag: v2.6.18-rc1~1081^2~77
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=39005d022ad221b76dc2de0ac62ef475a796433b;p=platform%2Fkernel%2Flinux-3.10.git

[PATCH] locks: don't do unnecessary allocations

posix_lock_file() always allocates new locks in advance, even if it's easy to
determine that no allocations will be needed.

Optimize these cases:

 - FL_ACCESS flag is set

 - Unlocking the whole range

Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---

diff --git a/fs/locks.c b/fs/locks.c
index c5ac6b4..2344f24 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -794,7 +794,8 @@ out:
 static int __posix_lock_file_conf(struct inode *inode, struct file_lock *request, struct file_lock *conflock)
 {
 	struct file_lock *fl;
-	struct file_lock *new_fl, *new_fl2;
+	struct file_lock *new_fl = NULL;
+	struct file_lock *new_fl2 = NULL;
 	struct file_lock *left = NULL;
 	struct file_lock *right = NULL;
 	struct file_lock **before;
@@ -803,9 +804,15 @@ static int __posix_lock_file_conf(struct inode *inode, struct file_lock *request
 	/*
 	 * We may need two file_lock structures for this operation,
 	 * so we get them in advance to avoid races.
+	 *
+	 * In some cases we can be sure, that no new locks will be needed
 	 */
-	new_fl = locks_alloc_lock();
-	new_fl2 = locks_alloc_lock();
+	if (!(request->fl_flags & FL_ACCESS) &&
+	    (request->fl_type != F_UNLCK ||
+	     request->fl_start != 0 || request->fl_end != OFFSET_MAX)) {
+		new_fl = locks_alloc_lock();
+		new_fl2 = locks_alloc_lock();
+	}
 
 	lock_kernel();
 	if (request->fl_type != F_UNLCK) {