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

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

1 files changed, 33 insertions, 3 deletions

diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
index 3f0e71b0e5d9..ee25e50e7c04 100644
--- 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);