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write support for preallocated blocks
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This patch adds write support to the uninitialized extents that get
created when a preallocation is done using fallocate(). It takes care of
splitting the extents into multiple (upto three) extents and merging the
new split extents with neighbouring ones, if possible.

Signed-off-by: Amit Arora <aarora@in.ibm.com>
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Amit Arora authored and Theodore Ts'o committed Jul 18, 2007
1 parent a2df2a6 commit 56055d3
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Showing 2 changed files with 225 additions and 32 deletions.
254 changes: 222 additions & 32 deletions fs/ext4/extents.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1140,6 +1140,53 @@ ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1,
return 0;
}

/*
* This function tries to merge the "ex" extent to the next extent in the tree.
* It always tries to merge towards right. If you want to merge towards
* left, pass "ex - 1" as argument instead of "ex".
* Returns 0 if the extents (ex and ex+1) were _not_ merged and returns
* 1 if they got merged.
*/
int ext4_ext_try_to_merge(struct inode *inode,
struct ext4_ext_path *path,
struct ext4_extent *ex)
{
struct ext4_extent_header *eh;
unsigned int depth, len;
int merge_done = 0;
int uninitialized = 0;

depth = ext_depth(inode);
BUG_ON(path[depth].p_hdr == NULL);
eh = path[depth].p_hdr;

while (ex < EXT_LAST_EXTENT(eh)) {
if (!ext4_can_extents_be_merged(inode, ex, ex + 1))
break;
/* merge with next extent! */
if (ext4_ext_is_uninitialized(ex))
uninitialized = 1;
ex->ee_len = cpu_to_le16(ext4_ext_get_actual_len(ex)
+ ext4_ext_get_actual_len(ex + 1));
if (uninitialized)
ext4_ext_mark_uninitialized(ex);

if (ex + 1 < EXT_LAST_EXTENT(eh)) {
len = (EXT_LAST_EXTENT(eh) - ex - 1)
* sizeof(struct ext4_extent);
memmove(ex + 1, ex + 2, len);
}
eh->eh_entries = cpu_to_le16(le16_to_cpu(eh->eh_entries) - 1);
merge_done = 1;
WARN_ON(eh->eh_entries == 0);
if (!eh->eh_entries)
ext4_error(inode->i_sb, "ext4_ext_try_to_merge",
"inode#%lu, eh->eh_entries = 0!", inode->i_ino);
}

return merge_done;
}

/*
* check if a portion of the "newext" extent overlaps with an
* existing extent.
Expand Down Expand Up @@ -1328,25 +1375,7 @@ int ext4_ext_insert_extent(handle_t *handle, struct inode *inode,

merge:
/* try to merge extents to the right */
while (nearex < EXT_LAST_EXTENT(eh)) {
if (!ext4_can_extents_be_merged(inode, nearex, nearex + 1))
break;
/* merge with next extent! */
if (ext4_ext_is_uninitialized(nearex))
uninitialized = 1;
nearex->ee_len = cpu_to_le16(ext4_ext_get_actual_len(nearex)
+ ext4_ext_get_actual_len(nearex + 1));
if (uninitialized)
ext4_ext_mark_uninitialized(nearex);

if (nearex + 1 < EXT_LAST_EXTENT(eh)) {
len = (EXT_LAST_EXTENT(eh) - nearex - 1)
* sizeof(struct ext4_extent);
memmove(nearex + 1, nearex + 2, len);
}
eh->eh_entries = cpu_to_le16(le16_to_cpu(eh->eh_entries)-1);
BUG_ON(eh->eh_entries == 0);
}
ext4_ext_try_to_merge(inode, path, nearex);

/* try to merge extents to the left */

Expand Down Expand Up @@ -2012,15 +2041,158 @@ void ext4_ext_release(struct super_block *sb)
#endif
}

/*
* This function is called by ext4_ext_get_blocks() if someone tries to write
* to an uninitialized extent. It may result in splitting the uninitialized
* extent into multiple extents (upto three - one initialized and two
* uninitialized).
* There are three possibilities:
* 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
*/
int ext4_ext_convert_to_initialized(handle_t *handle, struct inode *inode,
struct ext4_ext_path *path,
ext4_fsblk_t iblock,
unsigned long max_blocks)
{
struct ext4_extent *ex, newex;
struct ext4_extent *ex1 = NULL;
struct ext4_extent *ex2 = NULL;
struct ext4_extent *ex3 = NULL;
struct ext4_extent_header *eh;
unsigned int allocated, ee_block, ee_len, depth;
ext4_fsblk_t newblock;
int err = 0;
int ret = 0;

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 - (iblock - ee_block);
newblock = iblock - ee_block + ext_pblock(ex);
ex2 = ex;

/* ex1: ee_block to iblock - 1 : uninitialized */
if (iblock > ee_block) {
ex1 = ex;
ex1->ee_len = cpu_to_le16(iblock - ee_block);
ext4_ext_mark_uninitialized(ex1);
ex2 = &newex;
}
/*
* for sanity, update the length of the ex2 extent before
* we insert ex3, if ex1 is NULL. This is to avoid temporary
* overlap of blocks.
*/
if (!ex1 && allocated > max_blocks)
ex2->ee_len = cpu_to_le16(max_blocks);
/* ex3: to ee_block + ee_len : uninitialised */
if (allocated > max_blocks) {
unsigned int newdepth;
ex3 = &newex;
ex3->ee_block = cpu_to_le32(iblock + max_blocks);
ext4_ext_store_pblock(ex3, newblock + max_blocks);
ex3->ee_len = cpu_to_le16(allocated - max_blocks);
ext4_ext_mark_uninitialized(ex3);
err = ext4_ext_insert_extent(handle, inode, path, ex3);
if (err)
goto out;
/*
* The depth, and hence eh & ex might change
* as part of the insert above.
*/
newdepth = ext_depth(inode);
if (newdepth != depth) {
depth = newdepth;
path = ext4_ext_find_extent(inode, iblock, NULL);
if (IS_ERR(path)) {
err = PTR_ERR(path);
path = NULL;
goto out;
}
eh = path[depth].p_hdr;
ex = path[depth].p_ext;
if (ex2 != &newex)
ex2 = ex;
}
allocated = max_blocks;
}
/*
* If there was a change of depth as part of the
* insertion of ex3 above, we need to update the length
* of the ex1 extent again here
*/
if (ex1 && ex1 != ex) {
ex1 = ex;
ex1->ee_len = cpu_to_le16(iblock - ee_block);
ext4_ext_mark_uninitialized(ex1);
ex2 = &newex;
}
/* ex2: iblock to iblock + maxblocks-1 : initialised */
ex2->ee_block = cpu_to_le32(iblock);
ex2->ee_start = cpu_to_le32(newblock);
ext4_ext_store_pblock(ex2, newblock);
ex2->ee_len = cpu_to_le16(allocated);
if (ex2 != ex)
goto insert;
err = ext4_ext_get_access(handle, inode, path + depth);
if (err)
goto out;
/*
* New (initialized) extent starts from the first block
* in the current extent. i.e., ex2 == ex
* We have to see if it can be merged with the extent
* on the left.
*/
if (ex2 > EXT_FIRST_EXTENT(eh)) {
/*
* To merge left, pass "ex2 - 1" to try_to_merge(),
* since it merges towards right _only_.
*/
ret = ext4_ext_try_to_merge(inode, path, ex2 - 1);
if (ret) {
err = ext4_ext_correct_indexes(handle, inode, path);
if (err)
goto out;
depth = ext_depth(inode);
ex2--;
}
}
/*
* Try to Merge towards right. This might be required
* only when the whole extent is being written to.
* i.e. ex2 == ex and ex3 == NULL.
*/
if (!ex3) {
ret = ext4_ext_try_to_merge(inode, path, ex2);
if (ret) {
err = ext4_ext_correct_indexes(handle, inode, path);
if (err)
goto out;
}
}
/* Mark modified extent as dirty */
err = ext4_ext_dirty(handle, inode, path + depth);
goto out;
insert:
err = ext4_ext_insert_extent(handle, inode, path, &newex);
out:
return err ? err : allocated;
}

int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
ext4_fsblk_t iblock,
unsigned long max_blocks, struct buffer_head *bh_result,
int create, int extend_disksize)
{
struct ext4_ext_path *path = NULL;
struct ext4_extent_header *eh;
struct ext4_extent newex, *ex;
ext4_fsblk_t goal, newblock;
int err = 0, depth;
int err = 0, depth, ret;
unsigned long allocated = 0;

__clear_bit(BH_New, &bh_result->b_state);
Expand All @@ -2033,8 +2205,10 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
if (goal) {
if (goal == EXT4_EXT_CACHE_GAP) {
if (!create) {
/* block isn't allocated yet and
* user doesn't want to allocate it */
/*
* block isn't allocated yet and
* user doesn't want to allocate it
*/
goto out2;
}
/* we should allocate requested block */
Expand Down Expand Up @@ -2068,6 +2242,7 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
* this is why assert can't be put in ext4_ext_find_extent()
*/
BUG_ON(path[depth].p_ext == NULL && depth != 0);
eh = path[depth].p_hdr;

ex = path[depth].p_ext;
if (ex) {
Expand All @@ -2076,13 +2251,9 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
unsigned short ee_len;

/*
* Allow future support for preallocated extents to be added
* as an RO_COMPAT feature:
* Uninitialized extents are treated as holes, except that
* we avoid (fail) allocating new blocks during a write.
* we split out initialized portions during a write.
*/
if (le16_to_cpu(ex->ee_len) > EXT_MAX_LEN)
goto out2;
ee_len = ext4_ext_get_actual_len(ex);
/* if found extent covers block, simply return it */
if (iblock >= ee_block && iblock < ee_block + ee_len) {
Expand All @@ -2091,12 +2262,27 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
allocated = ee_len - (iblock - ee_block);
ext_debug("%d fit into %lu:%d -> %llu\n", (int) iblock,
ee_block, ee_len, newblock);

/* Do not put uninitialized extent in the cache */
if (!ext4_ext_is_uninitialized(ex))
if (!ext4_ext_is_uninitialized(ex)) {
ext4_ext_put_in_cache(inode, ee_block,
ee_len, ee_start,
EXT4_EXT_CACHE_EXTENT);
goto out;
goto out;
}
if (create == EXT4_CREATE_UNINITIALIZED_EXT)
goto out;
if (!create)
goto out2;

ret = ext4_ext_convert_to_initialized(handle, inode,
path, iblock,
max_blocks);
if (ret <= 0)
goto out2;
else
allocated = ret;
goto outnew;
}
}

Expand All @@ -2105,8 +2291,10 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
* we couldn't try to create block if create flag is zero
*/
if (!create) {
/* put just found gap into cache to speed up
* subsequent requests */
/*
* put just found gap into cache to speed up
* subsequent requests
*/
ext4_ext_put_gap_in_cache(inode, path, iblock);
goto out2;
}
Expand Down Expand Up @@ -2152,6 +2340,7 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,

/* previous routine could use block we allocated */
newblock = ext_pblock(&newex);
outnew:
__set_bit(BH_New, &bh_result->b_state);

/* Cache only when it is _not_ an uninitialized extent */
Expand Down Expand Up @@ -2221,7 +2410,8 @@ void ext4_ext_truncate(struct inode * inode, struct page *page)
err = ext4_ext_remove_space(inode, last_block);

/* In a multi-transaction truncate, we only make the final
* transaction synchronous. */
* transaction synchronous.
*/
if (IS_SYNC(inode))
handle->h_sync = 1;

Expand Down
3 changes: 3 additions & 0 deletions include/linux/ext4_fs_extents.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -205,6 +205,9 @@ static inline int ext4_ext_get_actual_len(struct ext4_extent *ext)

extern int ext4_extent_tree_init(handle_t *, struct inode *);
extern int ext4_ext_calc_credits_for_insert(struct inode *, struct ext4_ext_path *);
extern int ext4_ext_try_to_merge(struct inode *inode,
struct ext4_ext_path *path,
struct ext4_extent *);
extern unsigned int ext4_ext_check_overlap(struct inode *, struct ext4_extent *, struct ext4_ext_path *);
extern int ext4_ext_insert_extent(handle_t *, struct inode *, struct ext4_ext_path *, struct ext4_extent *);
extern int ext4_ext_walk_space(struct inode *, unsigned long, unsigned long, ext_prepare_callback, void *);
Expand Down

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