[PATCH 3/4] locks: don't do unnecessary allocations

[Miklos Szeredi]

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@xxxxxxxxxx>

Index: linux/fs/locks.c
===================================================================
--- linux.orig/fs/locks.c       2006-03-31 18:55:33.000000000 +0200
+++ linux/fs/locks.c    2006-03-31 18:55:33.000000000 +0200
@@ -795,7 +795,8 @@ int __posix_lock_file(struct inode *inod
                      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;
@@ -804,9 +805,15 @@ int __posix_lock_file(struct inode *inod
        /*
         * 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) {
-
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