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ext4: fix suboptimal seek_{data,hole} extents traversial
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It is ridiculous practice to scan inode block by block, this technique
applicable only for old indirect files. This takes significant amount
of time for really large files. Let's reuse ext4_fiemap which already
traverse inode-tree in most optimal meaner.

TESTCASE:
ftruncate64(fd, 0);
ftruncate64(fd, 1ULL << 40);
/* lseek will spin very long time */
lseek64(fd, 0, SEEK_DATA);
lseek64(fd, 0, SEEK_HOLE);

Original report: https://lkml.org/lkml/2014/10/16/620

Signed-off-by: Dmitry Monakhov <[email protected]>
Signed-off-by: Theodore Ts'o <[email protected]>
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@tytso
Dmitry Monakhov authored and tytso committed Dec 2, 2014
1 parent d952d69 commit 14516bb
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Showing 2 changed files with 108 additions and 116 deletions.
4 changes: 2 additions & 2 deletions fs/ext4/extents.c
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Original file line number Diff line number Diff line change
Expand Up @@ -5166,8 +5166,8 @@ int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,

/* fallback to generic here if not in extents fmt */
if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)))
return generic_block_fiemap(inode, fieinfo, start, len,
ext4_get_block);
return __generic_block_fiemap(inode, fieinfo, start, len,
ext4_get_block);

if (fiemap_check_flags(fieinfo, EXT4_FIEMAP_FLAGS))
return -EBADR;
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220 changes: 106 additions & 114 deletions fs/ext4/file.c
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Original file line number Diff line number Diff line change
Expand Up @@ -273,24 +273,19 @@ static int ext4_file_open(struct inode * inode, struct file * filp)
* we determine this extent as a data or a hole according to whether the
* page cache has data or not.
*/
static int ext4_find_unwritten_pgoff(struct inode *inode,
int whence,
struct ext4_map_blocks *map,
loff_t *offset)
static int ext4_find_unwritten_pgoff(struct inode *inode, int whence,
loff_t endoff, loff_t *offset)
{
struct pagevec pvec;
unsigned int blkbits;
pgoff_t index;
pgoff_t end;
loff_t endoff;
loff_t startoff;
loff_t lastoff;
int found = 0;

blkbits = inode->i_sb->s_blocksize_bits;
startoff = *offset;
lastoff = startoff;
endoff = (loff_t)(map->m_lblk + map->m_len) << blkbits;


index = startoff >> PAGE_CACHE_SHIFT;
end = endoff >> PAGE_CACHE_SHIFT;
Expand Down Expand Up @@ -408,147 +403,144 @@ static int ext4_find_unwritten_pgoff(struct inode *inode,
static loff_t ext4_seek_data(struct file *file, loff_t offset, loff_t maxsize)
{
struct inode *inode = file->f_mapping->host;
struct ext4_map_blocks map;
struct extent_status es;
ext4_lblk_t start, last, end;
loff_t dataoff, isize;
int blkbits;
int ret = 0;
struct fiemap_extent_info fie;
struct fiemap_extent ext[2];
loff_t next;
int i, ret = 0;

mutex_lock(&inode->i_mutex);

isize = i_size_read(inode);
if (offset >= isize) {
if (offset >= inode->i_size) {
mutex_unlock(&inode->i_mutex);
return -ENXIO;
}

blkbits = inode->i_sb->s_blocksize_bits;
start = offset >> blkbits;
last = start;
end = isize >> blkbits;
dataoff = offset;

do {
map.m_lblk = last;
map.m_len = end - last + 1;
ret = ext4_map_blocks(NULL, inode, &map, 0);
if (ret > 0 && !(map.m_flags & EXT4_MAP_UNWRITTEN)) {
if (last != start)
dataoff = (loff_t)last << blkbits;
fie.fi_flags = 0;
fie.fi_extents_max = 2;
fie.fi_extents_start = (struct fiemap_extent __user *) &ext;
while (1) {
mm_segment_t old_fs = get_fs();

fie.fi_extents_mapped = 0;
memset(ext, 0, sizeof(*ext) * fie.fi_extents_max);

set_fs(get_ds());
ret = ext4_fiemap(inode, &fie, offset, maxsize - offset);
set_fs(old_fs);
if (ret)
break;
}

/*
* If there is a delay extent at this offset,
* it will be as a data.
*/
ext4_es_find_delayed_extent_range(inode, last, last, &es);
if (es.es_len != 0 && in_range(last, es.es_lblk, es.es_len)) {
if (last != start)
dataoff = (loff_t)last << blkbits;
/* No extents found, EOF */
if (!fie.fi_extents_mapped) {
ret = -ENXIO;
break;
}
for (i = 0; i < fie.fi_extents_mapped; i++) {
next = (loff_t)(ext[i].fe_length + ext[i].fe_logical);

/*
* If there is a unwritten extent at this offset,
* it will be as a data or a hole according to page
* cache that has data or not.
*/
if (map.m_flags & EXT4_MAP_UNWRITTEN) {
int unwritten;
unwritten = ext4_find_unwritten_pgoff(inode, SEEK_DATA,
&map, &dataoff);
if (unwritten)
break;
}
if (offset < (loff_t)ext[i].fe_logical)
offset = (loff_t)ext[i].fe_logical;
/*
* If extent is not unwritten, then it contains valid
* data, mapped or delayed.
*/
if (!(ext[i].fe_flags & FIEMAP_EXTENT_UNWRITTEN))
goto out;

last++;
dataoff = (loff_t)last << blkbits;
} while (last <= end);
/*
* If there is a unwritten extent at this offset,
* it will be as a data or a hole according to page
* cache that has data or not.
*/
if (ext4_find_unwritten_pgoff(inode, SEEK_DATA,
next, &offset))
goto out;

if (ext[i].fe_flags & FIEMAP_EXTENT_LAST) {
ret = -ENXIO;
goto out;
}
offset = next;
}
}
if (offset > inode->i_size)
offset = inode->i_size;
out:
mutex_unlock(&inode->i_mutex);
if (ret)
return ret;

if (dataoff > isize)
return -ENXIO;

return vfs_setpos(file, dataoff, maxsize);
return vfs_setpos(file, offset, maxsize);
}

/*
* ext4_seek_hole() retrieves the offset for SEEK_HOLE.
* ext4_seek_hole() retrieves the offset for SEEK_HOLE
*/
static loff_t ext4_seek_hole(struct file *file, loff_t offset, loff_t maxsize)
{
struct inode *inode = file->f_mapping->host;
struct ext4_map_blocks map;
struct extent_status es;
ext4_lblk_t start, last, end;
loff_t holeoff, isize;
int blkbits;
int ret = 0;
struct fiemap_extent_info fie;
struct fiemap_extent ext[2];
loff_t next;
int i, ret = 0;

mutex_lock(&inode->i_mutex);

isize = i_size_read(inode);
if (offset >= isize) {
if (offset >= inode->i_size) {
mutex_unlock(&inode->i_mutex);
return -ENXIO;
}

blkbits = inode->i_sb->s_blocksize_bits;
start = offset >> blkbits;
last = start;
end = isize >> blkbits;
holeoff = offset;
fie.fi_flags = 0;
fie.fi_extents_max = 2;
fie.fi_extents_start = (struct fiemap_extent __user *)&ext;
while (1) {
mm_segment_t old_fs = get_fs();

do {
map.m_lblk = last;
map.m_len = end - last + 1;
ret = ext4_map_blocks(NULL, inode, &map, 0);
if (ret > 0 && !(map.m_flags & EXT4_MAP_UNWRITTEN)) {
last += ret;
holeoff = (loff_t)last << blkbits;
continue;
}
fie.fi_extents_mapped = 0;
memset(ext, 0, sizeof(*ext));

/*
* If there is a delay extent at this offset,
* we will skip this extent.
*/
ext4_es_find_delayed_extent_range(inode, last, last, &es);
if (es.es_len != 0 && in_range(last, es.es_lblk, es.es_len)) {
last = es.es_lblk + es.es_len;
holeoff = (loff_t)last << blkbits;
continue;
}
set_fs(get_ds());
ret = ext4_fiemap(inode, &fie, offset, maxsize - offset);
set_fs(old_fs);
if (ret)
break;

/*
* If there is a unwritten extent at this offset,
* it will be as a data or a hole according to page
* cache that has data or not.
*/
if (map.m_flags & EXT4_MAP_UNWRITTEN) {
int unwritten;
unwritten = ext4_find_unwritten_pgoff(inode, SEEK_HOLE,
&map, &holeoff);
if (!unwritten) {
last += ret;
holeoff = (loff_t)last << blkbits;
/* No extents found */
if (!fie.fi_extents_mapped)
break;

for (i = 0; i < fie.fi_extents_mapped; i++) {
next = (loff_t)(ext[i].fe_logical + ext[i].fe_length);
/*
* If extent is not unwritten, then it contains valid
* data, mapped or delayed.
*/
if (!(ext[i].fe_flags & FIEMAP_EXTENT_UNWRITTEN)) {
if (offset < (loff_t)ext[i].fe_logical)
goto out;
offset = next;
continue;
}
}

/* find a hole */
break;
} while (last <= end);
/*
* If there is a unwritten extent at this offset,
* it will be as a data or a hole according to page
* cache that has data or not.
*/
if (ext4_find_unwritten_pgoff(inode, SEEK_HOLE,
next, &offset))
goto out;

offset = next;
if (ext[i].fe_flags & FIEMAP_EXTENT_LAST)
goto out;
}
}
if (offset > inode->i_size)
offset = inode->i_size;
out:
mutex_unlock(&inode->i_mutex);
if (ret)
return ret;

if (holeoff > isize)
holeoff = isize;

return vfs_setpos(file, holeoff, maxsize);
return vfs_setpos(file, offset, maxsize);
}

/*
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