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Date: Tue, 28 Aug 2012 20:21:43 +0400
From: Dmitry Monakhov <dmonakhov@...nvz.org>
To: linux-ext4@...r.kernel.org
Cc: tytso@....edu, a-fujita@...jp.nec.com,
Dmitry Monakhov <dmonakhov@...nvz.org>
Subject: [PATCH 3/3] 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.
---
fs/ext4/move_extent.c | 96 ++++++++++++++++++++++++++++++++++++++++++++-----
1 files changed, 87 insertions(+), 9 deletions(-)
diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
index c5ca317..b62defa 100644
--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -629,6 +629,42 @@ mext_calc_swap_extents(struct ext4_extent *tmp_dext,
}
/**
+ * mext_check_range_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.
+ */
+int mext_check_range_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;
+ 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
@@ -663,9 +699,6 @@ 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)
@@ -764,8 +797,6 @@ out:
ext4_ext_invalidate_cache(orig_inode);
ext4_ext_invalidate_cache(donor_inode);
- double_up_write_data_sem(orig_inode, donor_inode);
-
return replaced_count;
}
@@ -807,10 +838,6 @@ move_extent_per_page(struct file *o_filp, struct inode *donor_inode,
int replaced_count = 0;
int blocks_per_page = PAGE_CACHE_SIZE >> orig_inode->i_blkbits;
- /*
- * It needs twice the amount of ordinary journal buffers because
- * inode and donor_inode may change each different metadata blocks.
- */
jblocks = ext4_writepage_trans_blocks(orig_inode) * 2;
if (segment_eq(get_fs(), KERNEL_DS))
@@ -819,6 +846,55 @@ move_extent_per_page(struct file *o_filp, struct inode *donor_inode,
orig_blk_offset = orig_page_offset * blocks_per_page +
data_offset_in_page;
+ /*
+ * If orig extent was uninitialized, but 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 necessery, just swap data blocks between orig
+ * and donor.
+ */
+ if (uninit) {
+ handle = ext4_journal_start(orig_inode, jblocks);
+ if (!handle) {
+ *err = -ENOMEM;
+ return 0;
+ }
+ page = find_or_create_page(mapping,orig_page_offset, GFP_NOFS);
+ if (!page) {
+ ext4_journal_stop(handle);
+ *err = -ENOMEM;
+ return 0;
+ }
+ double_down_write_data_sem(orig_inode, donor_inode);
+ /* If any of extents in range became initialized we have to
+ * fallback to data copying */
+ if (!mext_check_range_coverage(orig_inode, orig_blk_offset,
+ block_len_in_page, 1, err) ||
+ !mext_check_range_coverage(donor_inode, orig_blk_offset,
+ block_len_in_page, 1, &err2)) {
+ double_up_write_data_sem(orig_inode, donor_inode);
+ unlock_page(page);
+ page_cache_release(page);
+ ext4_journal_stop(handle);
+ if (*err || err2)
+ goto out;
+ goto data_copy;
+ }
+ if (!try_to_release_page(page, 0))
+ goto drop_data_sem;
+
+ if (!PageUptodate(page)) {
+ zero_user(page, 0, PAGE_SIZE);
+ SetPageUptodate(page);
+ }
+ 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 drop_page;
+ }
+data_copy:
offs = (long long)orig_blk_offset << orig_inode->i_blkbits;
/* Calculate data_size */
@@ -884,9 +960,11 @@ move_extent_per_page(struct file *o_filp, struct inode *donor_inode,
if (ext4_journal_extend(handle, jblocks) < 0)
goto write_end;
+ double_down_write_data_sem(orig_inode, donor_inode);
replaced_count = mext_replace_branches(handle, orig_inode, donor_inode,
orig_blk_offset, block_len_in_page,
&err2);
+ double_up_write_data_sem(orig_inode, donor_inode);
if (err2) {
if (replaced_count) {
block_len_in_page = replaced_count;
--
1.7.7.6
--
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