ext4: Support for synchronous DAX faults
We return IOMAP_F_DIRTY flag from ext4_iomap_begin() when asked to
prepare blocks for writing and the inode has some uncommitted metadata
changes. In the fault handler ext4_dax_fault() we then detect this case
(through VM_FAULT_NEEDDSYNC return value) and call helper
dax_finish_sync_fault() to flush metadata changes and insert page table
entry. Note that this will also dirty corresponding radix tree entry
which is what we want - fsync(2) will still provide data integrity
guarantees for applications not using userspace flushing. And
applications using userspace flushing can avoid calling fsync(2) and
thus avoid the performance overhead.
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 31db875..13a1989 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3394,6 +3394,19 @@ static int ext4_releasepage(struct page *page, gfp_t wait)
}
#ifdef CONFIG_FS_DAX
+static bool ext4_inode_datasync_dirty(struct inode *inode)
+{
+ journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
+
+ if (journal)
+ return !jbd2_transaction_committed(journal,
+ EXT4_I(inode)->i_datasync_tid);
+ /* Any metadata buffers to write? */
+ if (!list_empty(&inode->i_mapping->private_list))
+ return true;
+ return inode->i_state & I_DIRTY_DATASYNC;
+}
+
static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
unsigned flags, struct iomap *iomap)
{
@@ -3466,6 +3479,8 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
}
iomap->flags = 0;
+ if ((flags & IOMAP_WRITE) && ext4_inode_datasync_dirty(inode))
+ iomap->flags |= IOMAP_F_DIRTY;
iomap->bdev = inode->i_sb->s_bdev;
iomap->dax_dev = sbi->s_daxdev;
iomap->offset = first_block << blkbits;