From: Amit Arora <aarora@xxxxxxxxxx> Change on-disk format for extent to represent uninitialized/initialized extents This change was suggested by Andreas Dilger as part of the following post: http://www.mail-archive.com/linux-ext4@xxxxxxxxxxxxxxx/msg02445.html This patch changes the EXT_MAX_LEN value and extent code which marks/checks uninitialized extents. With this change it will be possible to have initialized extents with 2^15 blocks (earlier the max blocks we could have was 2^15 - 1). This way we can have better extent-to-block alignment. Now, maximum number of blocks we can have in an initialized extent is 2^15 and in an uninitialized extent is 2^15 - 1. Signed-off-by: Amit Arora <aarora@xxxxxxxxxx> Index: linux-2.6.22/fs/ext4/extents.c =================================================================== --- linux-2.6.22.orig/fs/ext4/extents.c +++ linux-2.6.22/fs/ext4/extents.c @@ -1106,7 +1106,7 @@ static int ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1, struct ext4_extent *ex2) { - unsigned short ext1_ee_len, ext2_ee_len; + unsigned short ext1_ee_len, ext2_ee_len, max_len; /* * Make sure that either both extents are uninitialized, or @@ -1115,6 +1115,11 @@ ext4_can_extents_be_merged(struct inode if (ext4_ext_is_uninitialized(ex1) ^ ext4_ext_is_uninitialized(ex2)) return 0; + if (ext4_ext_is_uninitialized(ex1)) + max_len = EXT_UNINIT_MAX_LEN; + else + max_len = EXT_INIT_MAX_LEN; + ext1_ee_len = ext4_ext_get_actual_len(ex1); ext2_ee_len = ext4_ext_get_actual_len(ex2); @@ -1127,7 +1132,7 @@ ext4_can_extents_be_merged(struct inode * as an RO_COMPAT feature, refuse to merge to extents if * this can result in the top bit of ee_len being set. */ - if (ext1_ee_len + ext2_ee_len > EXT_MAX_LEN) + if (ext1_ee_len + ext2_ee_len > max_len) return 0; #ifdef AGGRESSIVE_TEST if (le16_to_cpu(ex1->ee_len) >= 4) @@ -1814,7 +1819,11 @@ ext4_ext_rm_leaf(handle_t *handle, struc ex->ee_block = cpu_to_le32(block); ex->ee_len = cpu_to_le16(num); - if (uninitialized) + /* + * Do not mark uninitialized if all the blocks in the + * extent have been removed. + */ + if (uninitialized && num) ext4_ext_mark_uninitialized(ex); err = ext4_ext_dirty(handle, inode, path + depth); @@ -2307,6 +2316,18 @@ int ext4_ext_get_blocks(handle_t *handle /* allocate new block */ goal = ext4_ext_find_goal(inode, path, iblock); + /* + * See if request is beyond maximum number of blocks we can have in + * a single extent. For an initialized extent this limit is + * EXT_INIT_MAX_LEN and for an uninitialized extent this limit is + * EXT_UNINIT_MAX_LEN. + */ + if (max_blocks > EXT_INIT_MAX_LEN && create != EXT4_CREATE_UNINITIALIZED_EXT) + max_blocks = EXT_INIT_MAX_LEN; + else if (max_blocks > EXT_UNINIT_MAX_LEN && + create == EXT4_CREATE_UNINITIALIZED_EXT) + max_blocks = EXT_UNINIT_MAX_LEN; + /* Check if we can really insert (iblock)::(iblock+max_blocks) extent */ newex.ee_block = cpu_to_le32(iblock); newex.ee_len = cpu_to_le16(max_blocks); Index: linux-2.6.22/include/linux/ext4_fs_extents.h =================================================================== --- linux-2.6.22.orig/include/linux/ext4_fs_extents.h +++ linux-2.6.22/include/linux/ext4_fs_extents.h @@ -141,7 +141,25 @@ typedef int (*ext_prepare_callback)(stru #define EXT_MAX_BLOCK 0xffffffff -#define EXT_MAX_LEN ((1UL << 15) - 1) +/* + * EXT_INIT_MAX_LEN is the maximum number of blocks we can have in an + * initialized extent. This is 2^15 and not (2^16 - 1), since we use the + * MSB of ee_len field in the extent datastructure to signify if this + * particular extent is an initialized extent or an uninitialized (i.e. + * preallocated). + * EXT_UNINIT_MAX_LEN is the maximum number of blocks we can have in an + * uninitialized extent. + * If ee_len is <= 0x8000, it is an initialized extent. Otherwise, it is an + * uninitialized one. In other words, if MSB of ee_len is set, it is an + * uninitialized extent with only one special scenario when ee_len = 0x8000. + * In this case we can not have an uninitialized extent of zero length and + * thus we make it as a special case of initialized extent with 0x8000 length. + * This way we get better extent-to-group alignment for initialized extents. + * Hence, the maximum number of blocks we can have in an *initialized* + * extent is 2^15 (32768) and in an *uninitialized* extent is 2^15-1 (32767). + */ +#define EXT_INIT_MAX_LEN (1UL << 15) +#define EXT_UNINIT_MAX_LEN (EXT_INIT_MAX_LEN - 1) #define EXT_FIRST_EXTENT(__hdr__) \ @@ -190,17 +208,21 @@ ext4_ext_invalidate_cache(struct inode * static inline void ext4_ext_mark_uninitialized(struct ext4_extent *ext) { + /* We can not have an uninitialized extent of zero length! */ + BUG_ON((le16_to_cpu(ext->ee_len) & ~0x8000) == 0); ext->ee_len |= cpu_to_le16(0x8000); } static inline int ext4_ext_is_uninitialized(struct ext4_extent *ext) { - return (int)(le16_to_cpu((ext)->ee_len) & 0x8000); + /* Extent with ee_len of 0x8000 is treated as an initialized extent */ + return (le16_to_cpu(ext->ee_len) > 0x8000); } static inline int ext4_ext_get_actual_len(struct ext4_extent *ext) { - return (int)(le16_to_cpu((ext)->ee_len) & 0x7FFF); + return (le16_to_cpu(ext->ee_len) <= 0x8000 ? le16_to_cpu(ext->ee_len) : + (le16_to_cpu(ext->ee_len) - 0x8000)); } extern int ext4_extent_tree_init(handle_t *, struct inode *); - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
