btrfs: inline btrfs_tree_lock() and btrfs_tree_read_lock()

The functions btrfs_tree_lock() and btrfs_tree_read_lock() are very
trivial so that can be made inline and avoid call overhead, as they
are very often called inside critical sections (when searching a btree
for example, attempting to lock a child node/leaf while holding a lock
on the parent).

So make them static inline, which even reduces the size of the btrfs
module a little bit.

Before this change:

   $ size fs/btrfs/btrfs.ko
      text	   data	    bss	    dec	    hex	filename
   1718786	 156276	  16920	1891982	 1cde8e	fs/btrfs/btrfs.ko

After this change:

   $ size fs/btrfs/btrfs.ko
      text	   data	    bss	    dec	    hex	filename
   1718650	 156260	  16920	1891830	 1cddf6	fs/btrfs/btrfs.ko

Running fs_mark also showed a tiny improvement with this script:

   $ cat test.sh
   #!/bin/bash

   DEV=/dev/nullb0
   MNT=/mnt/nullb0
   FILES=100000
   THREADS=$(nproc --all)

   echo "performance" | \
       tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

   umount $DEV &> /dev/null
   mkfs.btrfs -f $DEV
   mount $DEV $MNT

   OPTS="-S 0 -L 5 -n $FILES -s 0 -t $THREADS -k"
   for ((i = 1; i <= $THREADS; i++)); do
        OPTS="$OPTS -d $MNT/d$i"
   done

   fs_mark $OPTS

   umount $MNT

Before this change:

   FSUse%        Count         Size    Files/sec     App Overhead
       10      1200000            0     180894.0         10705410
       16      2400000            0     228211.4         10765738
       23      3600000            0     215969.6         11011072
       30      4800000            0     199077.1         11145587
       46      6000000            0     176624.1         11658470

After this change:

   FSUse%        Count         Size    Files/sec     App Overhead
       10      1200000            0     185312.3         10708377
       16      2400000            0     229320.4         10858013
       23      3600000            0     217958.7         11006167
       30      4800000            0     205122.9         11112899
       46      6000000            0     178039.1         11438852

Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>

fs/btrfs/locking.c

@@ -147,11 +147,6 @@ void __btrfs_tree_read_lock(struct extent_buffer *eb, enum btrfs_lock_nesting ne
 	trace_btrfs_tree_read_lock(eb, start_ns);
 }
 
-void btrfs_tree_read_lock(struct extent_buffer *eb)
-{
-	__btrfs_tree_read_lock(eb, BTRFS_NESTING_NORMAL);
-}
-
 /*
  * Try-lock for read.
  *
@@ -211,11 +206,6 @@ void __btrfs_tree_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest)
 	trace_btrfs_tree_lock(eb, start_ns);
 }
 
-void btrfs_tree_lock(struct extent_buffer *eb)
-{
-	__btrfs_tree_lock(eb, BTRFS_NESTING_NORMAL);
-}
-
 /*
  * Release the write lock.
  */

fs/btrfs/locking.h

@@ -164,11 +164,21 @@ static_assert(BTRFS_NESTING_MAX <= MAX_LOCKDEP_SUBCLASSES,
 	      "too many lock subclasses defined");
 
 void __btrfs_tree_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest);
-void btrfs_tree_lock(struct extent_buffer *eb);
+
+static inline void btrfs_tree_lock(struct extent_buffer *eb)
+{
+	__btrfs_tree_lock(eb, BTRFS_NESTING_NORMAL);
+}
+
 void btrfs_tree_unlock(struct extent_buffer *eb);
 
 void __btrfs_tree_read_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest);
-void btrfs_tree_read_lock(struct extent_buffer *eb);
+
+static inline void btrfs_tree_read_lock(struct extent_buffer *eb)
+{
+	__btrfs_tree_read_lock(eb, BTRFS_NESTING_NORMAL);
+}
+
 void btrfs_tree_read_unlock(struct extent_buffer *eb);
 int btrfs_try_tree_read_lock(struct extent_buffer *eb);
 int btrfs_try_tree_write_lock(struct extent_buffer *eb);