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ext4: reimplement uninit extent optimization for move_extent_per_page()

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Uninitialized extent may became initialized(parallel writeback task)
at any moment after we drop i_data_sem, so we have to recheck extent's
state after we hold page's lock and i_data_sem.

If we about to change page's mapping we must hold page's lock in order to
serialize other users.

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Dmitry Monakhov 2012-09-26 12:54:52 -04:00 committed by Theodore Ts'o
parent bb55748805
commit 8c85447391
1 changed files with 76 additions and 5 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

81
fs/ext4/move_extent.c
View file

@ -594,6 +594,43 @@ mext_calc_swap_extents(struct ext4_extent *tmp_dext,
return 0;
}
/**
* mext_check_coverage - Check that all extents in range has the same type
*
* @inode: inode in question
* @from: block offset of inode
* @count: block count to be checked
* @uninit: extents expected to be uninitialized
* @err: pointer to save error value
*
* Return 1 if all extents in range has expected type, and zero otherwise.
*/
static int
mext_check_coverage(struct inode *inode, ext4_lblk_t from, ext4_lblk_t count,
int uninit, int *err)
{
struct ext4_ext_path *path = NULL;
struct ext4_extent *ext;
ext4_lblk_t last = from + count;
while (from < last) {
*err = get_ext_path(inode, from, &path);
if (*err)
return 0;
ext = path[ext_depth(inode)].p_ext;
if (!ext) {
ext4_ext_drop_refs(path);
return 0;
}
if (uninit != ext4_ext_is_uninitialized(ext)) {
ext4_ext_drop_refs(path);
return 0;
}
from += ext4_ext_get_actual_len(ext);
ext4_ext_drop_refs(path);
}
return 1;
}
/**
* mext_replace_branches - Replace original extents with new extents
*
@ -629,9 +666,6 @@ mext_replace_branches(handle_t *handle, struct inode *orig_inode,
int replaced_count = 0;
int dext_alen;
/* Protect extent trees against block allocations via delalloc */
double_down_write_data_sem(orig_inode, donor_inode);
/* Get the original extent for the block "orig_off" */
*err = get_ext_path(orig_inode, orig_off, &orig_path);
if (*err)
@ -730,8 +764,6 @@ mext_replace_branches(handle_t *handle, struct inode *orig_inode,
ext4_ext_invalidate_cache(orig_inode);
ext4_ext_invalidate_cache(donor_inode);
double_up_write_data_sem(orig_inode, donor_inode);
return replaced_count;
}
@ -925,7 +957,46 @@ move_extent_per_page(struct file *o_filp, struct inode *donor_inode,
pagep);
if (unlikely(*err < 0))
goto stop_journal;
/*
* If orig extent was uninitialized it can become initialized
* at any time after i_data_sem was dropped, in order to
* serialize with delalloc we have recheck extent while we
* hold page's lock, if it is still the case data copy is not
* necessary, just swap data blocks between orig and donor.
*/
if (uninit) {
double_down_write_data_sem(orig_inode, donor_inode);
/* If any of extents in range became initialized we have to
* fallback to data copying */
uninit = mext_check_coverage(orig_inode, orig_blk_offset,
block_len_in_page, 1, err);
if (*err)
goto drop_data_sem;
uninit &= mext_check_coverage(donor_inode, orig_blk_offset,
block_len_in_page, 1, err);
if (*err)
goto drop_data_sem;
if (!uninit) {
double_up_write_data_sem(orig_inode, donor_inode);
goto data_copy;
}
if ((page_has_private(pagep[0]) &&
!try_to_release_page(pagep[0], 0)) ||
(page_has_private(pagep[1]) &&
!try_to_release_page(pagep[1], 0))) {
*err = -EBUSY;
goto drop_data_sem;
}
replaced_count = mext_replace_branches(handle, orig_inode,
donor_inode, orig_blk_offset,
block_len_in_page, err);
drop_data_sem:
double_up_write_data_sem(orig_inode, donor_inode);
goto unlock_pages;
}
data_copy:
*err = mext_page_mkuptodate(pagep[0], from, from + replaced_size);
if (*err)
goto unlock_pages;