ext4: reimplement uninit extent optimization for move_extent_per_page()
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>
diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
index c87a746..c2e47da 100644
--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -595,6 +595,43 @@
}
/**
+ * 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
*
* @handle: journal handle
@@ -629,9 +666,6 @@
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 @@
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 @@
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;