[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>

1 files changed, 10 insertions, 3 deletions

diff --git a/fs/locks.c b/fs/locks.c
index c5ac6b40e766..2344f241c687 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) {