Btrfs: While doing checksums on bios, cache the extent_buffer mapping

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

diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
index 3f0e71b..ee25e50 100644 (file)
--- a/fs/btrfs/file-item.c
+++ b/fs/btrfs/file-item.c
@@ -156,6 +156,11 @@ int btrfs_csum_file_blocks(struct btrfs_trans_handle *trans,
        int bio_index = 0;
        struct bio_vec *bvec = bio->bi_io_vec;
        char *data;
+       char *eb_map;
+       char *eb_token;
+       unsigned long map_len;
+       unsigned long map_start;
+
 
        path = btrfs_alloc_path();
        BUG_ON(!path);
@@ -272,6 +277,7 @@ found:
        item_end = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_csum_item);
        item_end = (struct btrfs_csum_item *)((unsigned char *)item_end +
                                      btrfs_item_size_nr(leaf, path->slots[0]));
+       eb_token = NULL;
 next_bvec:
        data = kmap_atomic(bvec->bv_page, KM_IRQ0);
        csum_result = ~(u32)0;
@@ -283,15 +289,39 @@ next_bvec:
                printk("csum result is 0 for inode %lu offset %Lu\n", inode->i_ino, offset);
        }
 
-       write_extent_buffer(leaf, &csum_result, (unsigned long)item,
-                           BTRFS_CRC32_SIZE);
+       if (!eb_token ||
+          (unsigned long)item  + BTRFS_CRC32_SIZE >= map_start + map_len) {
+               int err;
+
+               if (eb_token)
+                       unmap_extent_buffer(leaf, eb_token, KM_IRQ1);
+               eb_token = NULL;
+               err = map_private_extent_buffer(leaf, (unsigned long)item,
+                                               BTRFS_CRC32_SIZE,
+                                               &eb_token, &eb_map,
+                                               &map_start, &map_len, KM_IRQ1);
+               if (err)
+                       eb_token = NULL;
+       }
+       if (eb_token) {
+               memcpy(eb_token + ((unsigned long)item & (PAGE_CACHE_SIZE - 1)),
+                      &csum_result, BTRFS_CRC32_SIZE);
+       } else {
+               write_extent_buffer(leaf, &csum_result, (unsigned long)item,
+                                   BTRFS_CRC32_SIZE);
+       }
        bio_index++;
        bvec++;
        if (bio_index < bio->bi_vcnt) {
-               item = (struct btrfs_csum_item *)((char *)item + BTRFS_CRC32_SIZE);
+               item = (struct btrfs_csum_item *)((char *)item +
+                                                 BTRFS_CRC32_SIZE);
                if (item < item_end)
                        goto next_bvec;
        }
+       if (eb_token) {
+               unmap_extent_buffer(leaf, eb_token, KM_IRQ1);
+               eb_token = NULL;
+       }
        btrfs_mark_buffer_dirty(path->nodes[0]);
        if (bio_index < bio->bi_vcnt) {
                btrfs_release_path(root, path);