btrfs: optimize split page write in btrfs_set_##bits

The helper write_extent_buffer is called to do write of the data
spanning two extent buffer pages. As the size is known, we can do the
write directly in two steps.  This removes one function call and
compiler can optimize memcpy as the sizes are known at compile time.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/struct-funcs.c b/fs/btrfs/struct-funcs.c
index 63cab91507f83d06dafcc9d3047bd9c877a75659..7987d3910660011e3def078b2b99b486a0202ebe 100644 (file)
--- a/fs/btrfs/struct-funcs.c
+++ b/fs/btrfs/struct-funcs.c
@@ -141,18 +141,22 @@ void btrfs_set_##bits(const struct extent_buffer *eb, void *ptr,  \
 {                                                                      \
        const unsigned long member_offset = (unsigned long)ptr + off;   \
        const unsigned long oip = offset_in_page(member_offset);        \
+       const unsigned long idx = member_offset >> PAGE_SHIFT;          \
+       char *kaddr = page_address(eb->pages[idx]);                     \
        const int size = sizeof(u##bits);                               \
-       __le##bits leres;                                               \
+       const int part = PAGE_SIZE - oip;                               \
+       u8 lebytes[sizeof(u##bits)];                                    \
                                                                        \
        ASSERT(check_setget_bounds(eb, ptr, off, size));                \
        if (oip + size <= PAGE_SIZE) {                                  \
-               const unsigned long idx = member_offset >> PAGE_SHIFT;  \
-               char *kaddr = page_address(eb->pages[idx]);             \
                put_unaligned_le##bits(val, kaddr + oip);               \
                return;                                                 \
        }                                                               \
-       leres = cpu_to_le##bits(val);                                   \
-       write_extent_buffer(eb, &leres, member_offset, size);           \
+                                                                       \
+       put_unaligned_le##bits(val, lebytes);                           \
+       memcpy(kaddr + oip, lebytes, part);                             \
+       kaddr = page_address(eb->pages[idx + 1]);                       \
+       memcpy(kaddr, lebytes + part, size - part);                     \
 }
 
 DEFINE_BTRFS_SETGET_BITS(8)