diff options
Diffstat (limited to 'fs/ext4/extents.c')
| -rw-r--r-- | fs/ext4/extents.c | 93 |
1 files changed, 93 insertions, 0 deletions
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index c2ac06c..8b6a17b 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -2919,12 +2919,23 @@ out: * a> There is no split required: Entire extent should be initialized * b> Splits in two extents: Write is happening at either end of the extent * c> Splits in three extents: Somone is writing in middle of the extent + * + * Pre-conditions: + * - The extent pointed to by 'path' is uninitialized. + * - The extent pointed to by 'path' contains a superset + * of the logical span [map->m_lblk, map->m_lblk + map->m_len). + * + * Post-conditions on success: + * - the returned value is the number of blocks beyond map->l_lblk + * that are allocated and initialized. + * It is guaranteed to be >= map->m_len. */ static int ext4_ext_convert_to_initialized(handle_t *handle, struct inode *inode, struct ext4_map_blocks *map, struct ext4_ext_path *path) { + struct ext4_extent_header *eh; struct ext4_map_blocks split_map; struct ext4_extent zero_ex; struct ext4_extent *ex; @@ -2944,11 +2955,93 @@ static int ext4_ext_convert_to_initialized(handle_t *handle, eof_block = map->m_lblk + map->m_len; depth = ext_depth(inode); + eh = path[depth].p_hdr; ex = path[depth].p_ext; ee_block = le32_to_cpu(ex->ee_block); ee_len = ext4_ext_get_actual_len(ex); allocated = ee_len - (map->m_lblk - ee_block); + trace_ext4_ext_convert_to_initialized_enter(inode, map, ex); + + /* Pre-conditions */ + BUG_ON(!ext4_ext_is_uninitialized(ex)); + BUG_ON(!in_range(map->m_lblk, ee_block, ee_len)); + BUG_ON(map->m_lblk + map->m_len > ee_block + ee_len); + + /* + * Attempt to transfer newly initialized blocks from the currently + * uninitialized extent to its left neighbor. This is much cheaper + * than an insertion followed by a merge as those involve costly + * memmove() calls. This is the common case in steady state for + * workloads doing fallocate(FALLOC_FL_KEEP_SIZE) followed by append + * writes. + * + * Limitations of the current logic: + * - L1: we only deal with writes at the start of the extent. + * The approach could be extended to writes at the end + * of the extent but this scenario was deemed less common. + * - L2: we do not deal with writes covering the whole extent. + * This would require removing the extent if the transfer + * is possible. + * - L3: we only attempt to merge with an extent stored in the + * same extent tree node. + */ + if ((map->m_lblk == ee_block) && /*L1*/ + (map->m_len < ee_len) && /*L2*/ + (ex > EXT_FIRST_EXTENT(eh))) { /*L3*/ + struct ext4_extent *prev_ex; + ext4_lblk_t prev_lblk; + ext4_fsblk_t prev_pblk, ee_pblk; + unsigned int prev_len, write_len; + + prev_ex = ex - 1; + prev_lblk = le32_to_cpu(prev_ex->ee_block); + prev_len = ext4_ext_get_actual_len(prev_ex); + prev_pblk = ext4_ext_pblock(prev_ex); + ee_pblk = ext4_ext_pblock(ex); + write_len = map->m_len; + + /* + * A transfer of blocks from 'ex' to 'prev_ex' is allowed + * upon those conditions: + * - C1: prev_ex is initialized, + * - C2: prev_ex is logically abutting ex, + * - C3: prev_ex is physically abutting ex, + * - C4: prev_ex can receive the additional blocks without + * overflowing the (initialized) length limit. + */ + if ((!ext4_ext_is_uninitialized(prev_ex)) && /*C1*/ + ((prev_lblk + prev_len) == ee_block) && /*C2*/ + ((prev_pblk + prev_len) == ee_pblk) && /*C3*/ + (prev_len < (EXT_INIT_MAX_LEN - write_len))) { /*C4*/ + err = ext4_ext_get_access(handle, inode, path + depth); + if (err) + goto out; + + trace_ext4_ext_convert_to_initialized_fastpath(inode, + map, ex, prev_ex); + + /* Shift the start of ex by 'write_len' blocks */ + ex->ee_block = cpu_to_le32(ee_block + write_len); + ext4_ext_store_pblock(ex, ee_pblk + write_len); + ex->ee_len = cpu_to_le16(ee_len - write_len); + ext4_ext_mark_uninitialized(ex); /* Restore the flag */ + + /* Extend prev_ex by 'write_len' blocks */ + prev_ex->ee_len = cpu_to_le16(prev_len + write_len); + + /* Mark the block containing both extents as dirty */ + ext4_ext_dirty(handle, inode, path + depth); + + /* Update path to point to the right extent */ + path[depth].p_ext = prev_ex; + + /* Result: number of initialized blocks past m_lblk */ + allocated = write_len; + goto out; + } + } + WARN_ON(map->m_lblk < ee_block); /* * It is safe to convert extent to initialized via explicit |
