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authorAmit Arora <aarora@in.ibm.com>2007-07-18 09:02:56 -0400
committerTheodore Ts'o <tytso@mit.edu>2007-07-18 09:02:56 -0400
commit749269facaf87f6e516c3af12763e03181b9c139 (patch)
tree5c8a2091d4b1ce7636de404a1366bd174b4634fd
parent56055d3ae4cc7fa6d2b10885f20269de8a989ed7 (diff)
Change on-disk format to support 2^15 uninitialized extents
This change was suggested by Andreas Dilger. 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@in.ibm.com>
-rw-r--r--fs/ext4/extents.c28
-rw-r--r--include/linux/ext4_fs_extents.h31
2 files changed, 52 insertions, 7 deletions
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index ded3d469f97..77146b826a1 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -1107,7 +1107,7 @@ 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
@@ -1116,6 +1116,11 @@ ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1,
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);
@@ -1128,7 +1133,7 @@ ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1,
* 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)
@@ -1815,7 +1820,11 @@ ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
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);
@@ -2308,6 +2317,19 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
/* 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);
diff --git a/include/linux/ext4_fs_extents.h b/include/linux/ext4_fs_extents.h
index edf49ec89ea..81406f3655d 100644
--- a/include/linux/ext4_fs_extents.h
+++ b/include/linux/ext4_fs_extents.h
@@ -141,7 +141,25 @@ typedef int (*ext_prepare_callback)(struct inode *, struct ext4_ext_path *,
#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 +208,22 @@ ext4_ext_invalidate_cache(struct inode *inode)
static inline void ext4_ext_mark_uninitialized(struct ext4_extent *ext)
{
- ext->ee_len |= cpu_to_le16(0x8000);
+ /* We can not have an uninitialized extent of zero length! */
+ BUG_ON((le16_to_cpu(ext->ee_len) & ~EXT_INIT_MAX_LEN) == 0);
+ ext->ee_len |= cpu_to_le16(EXT_INIT_MAX_LEN);
}
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) > EXT_INIT_MAX_LEN);
}
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) <= EXT_INIT_MAX_LEN ?
+ le16_to_cpu(ext->ee_len) :
+ (le16_to_cpu(ext->ee_len) - EXT_INIT_MAX_LEN));
}
extern int ext4_extent_tree_init(handle_t *, struct inode *);