Btrfs: Optimizations for the extent_buffer code

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 43 insertions, 5 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index c4b829806855..30fbbd7221a9 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -22,6 +22,7 @@
 #include <linux/fs.h>
 #include <linux/workqueue.h>
 #include <linux/completion.h>
+#include <asm/kmap_types.h>
 #include "bit-radix.h"
 #include "extent_map.h"
 
@@ -431,15 +432,52 @@ struct btrfs_root {
 static inline u##bits btrfs_##name(struct extent_buffer *eb,            \
                                    type *s)                             \
 {                                                                       \
-        __le##bits res;                                                 \
-        read_eb_member(eb, s, type, member, &res);                      \
-        return le##bits##_to_cpu(res);                                  \
+        int err;                                                        \
+        char *map_token;                                                \
+        char *kaddr;                                                    \
+        unsigned long map_start;                                        \
+        unsigned long map_len;                                          \
+        unsigned long offset = (unsigned long)s +                       \
+                                offsetof(type, member);                 \
+        err = map_extent_buffer(eb, offset,                             \
+                                sizeof(((type *)0)->member),            \
+                                &map_token, &kaddr,                     \
+                                &map_start, &map_len, KM_USER0);        \
+        if (!err) {                                                     \
+                __le##bits *tmp = (__le##bits *)(kaddr + offset -       \
+                                               map_start);              \
+                u##bits res = le##bits##_to_cpu(*tmp);                  \
+                unmap_extent_buffer(eb, map_token, KM_USER0);           \
+                return res;                                             \
+        } else {                                                        \
+                __le##bits res;                                         \
+                read_eb_member(eb, s, type, member, &res);              \
+                return le##bits##_to_cpu(res);                          \
+        }                                                               \
 }                                                                       \
 static inline void btrfs_set_##name(struct extent_buffer *eb,           \
                                     type *s, u##bits val)               \
 {                                                                       \
-        val = cpu_to_le##bits(val);                                     \
-        write_eb_member(eb, s, type, member, &val);                     \
+        int err;                                                        \
+        char *map_token;                                                \
+        char *kaddr;                                                    \
+        unsigned long map_start;                                        \
+        unsigned long map_len;                                          \
+        unsigned long offset = (unsigned long)s +                       \
+                                offsetof(type, member);                 \
+        err = map_extent_buffer(eb, offset,                             \
+                                sizeof(((type *)0)->member),            \
+                                &map_token, &kaddr,                     \
+                                &map_start, &map_len, KM_USER0);        \
+        if (!err) {                                                     \
+                __le##bits *tmp = (__le##bits *)(kaddr + offset -       \
+                                               map_start);              \
+                *tmp = cpu_to_le##bits(val);                            \
+                unmap_extent_buffer(eb, map_token, KM_USER0);           \
+        } else {                                                        \
+                val = cpu_to_le##bits(val);                             \
+                write_eb_member(eb, s, type, member, &val);             \
+        }                                                               \
 }
 
 #define BTRFS_SETGET_HEADER_FUNCS(name, type, member, bits)             \