Btrfs: Optimize csum insertion to create larger items when possible

This reduces the number of calls to btrfs_extend_item and greatly lowers
the cpu usage while writing large files.

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

3 files changed, 38 insertions, 2 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 1d2b54150075..70e143b13577 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -991,6 +991,7 @@ int btrfs_lookup_file_extent(struct btrfs_trans_handle *trans,
                              u64 bytenr, int mod);
 int btrfs_csum_file_block(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root,
+                          struct inode *inode,
                           u64 objectid, u64 offset,
                           char *data, size_t len);
 struct btrfs_csum_item *btrfs_lookup_csum(struct btrfs_trans_handle *trans,
diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
index 10a4c7408600..482a2b615327 100644
--- a/fs/btrfs/file-item.c
+++ b/fs/btrfs/file-item.c
@@ -133,17 +133,22 @@ int btrfs_lookup_file_extent(struct btrfs_trans_handle *trans,
 
 int btrfs_csum_file_block(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root,
+                          struct inode *inode,
                           u64 objectid, u64 offset,
                           char *data, size_t len)
 {
         int ret;
         struct btrfs_key file_key;
         struct btrfs_key found_key;
+        u64 next_offset = (u64)-1;
+        int found_next = 0;
         struct btrfs_path *path;
         struct btrfs_csum_item *item;
         struct extent_buffer *leaf = NULL;
         u64 csum_offset;
         u32 csum_result = ~(u32)0;
+        u32 nritems;
+        u32 ins_size;
 
         path = btrfs_alloc_path();
         BUG_ON(!path);
@@ -168,7 +173,27 @@ int btrfs_csum_file_block(struct btrfs_trans_handle *trans,
                         goto insert;
                 }
         } else {
+                int slot = path->slots[0] + 1;
                 /* we didn't find a csum item, insert one */
+                nritems = btrfs_header_nritems(path->nodes[0]);
+                if (path->slots[0] >= nritems - 1) {
+                        ret = btrfs_next_leaf(root, path);
+                        if (ret == 1) {
+                                found_next = 1;
+                        } else if (ret == 0) {
+                                slot = 0;
+                        } else {
+                                goto insert;
+                        }
+                }
+                btrfs_item_key_to_cpu(path->nodes[0], &found_key, slot);
+                if (found_key.objectid != objectid ||
+                    found_key.type != BTRFS_CSUM_ITEM_KEY) {
+                        found_next = 1;
+                        goto insert;
+                }
+                next_offset = found_key.offset;
+                found_next = 1;
                 goto insert;
         }
 
@@ -211,8 +236,18 @@ int btrfs_csum_file_block(struct btrfs_trans_handle *trans,
 insert:
         btrfs_release_path(root, path);
         csum_offset = 0;
+        if (found_next) {
+                u64 tmp = min((u64)i_size_read(inode), next_offset);
+                tmp -= offset + root->sectorsize - 1;
+                tmp >>= root->fs_info->sb->s_blocksize_bits;
+                tmp = max((u64)1, tmp);
+                tmp = min(tmp, (u64)MAX_CSUM_ITEMS(root));
+                ins_size = BTRFS_CRC32_SIZE * tmp;
+        } else {
+                ins_size = BTRFS_CRC32_SIZE;
+        }
         ret = btrfs_insert_empty_item(trans, root, path, &file_key,
-                                      BTRFS_CRC32_SIZE);
+                                      ins_size);
         if (ret < 0)
                 goto fail;
         if (ret != 0) {
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 02d802cdd59b..7efc0470abf1 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -118,7 +118,7 @@ int btrfs_writepage_io_hook(struct page *page, u64 start, u64 end)
         trans = btrfs_start_transaction(root, 1);
         btrfs_set_trans_block_group(trans, inode);
         kaddr = kmap(page);
-        btrfs_csum_file_block(trans, root, inode->i_ino,
+        btrfs_csum_file_block(trans, root, inode, inode->i_ino,
                               start, kaddr + offset, end - start + 1);
         kunmap(page);
         ret = btrfs_end_transaction(trans, root);