The conversion to iomap seems to have lost the ability to
conditionally /not/ prezero dax blocks. This leads to
double writes which cuts throughput in half in some
cases.
This puts back the old conditional zeroing logic.
Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
---
I might be completely missing something here, i.e. whether
the change may have been intentional, etc. The patch is
only lightly tested but a which check here seems to DTRT.
Thanks,
-Eric
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index c774bdc..9179a59 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3423,6 +3423,7 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
int dio_credits;
handle_t *handle;
int retries = 0;
+ int flags;
/* Trim mapping request to maximum we can map at once for DIO */
if (map.m_len > DIO_MAX_BLOCKS)
@@ -3440,8 +3441,16 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
if (IS_ERR(handle))
return PTR_ERR(handle);
- ret = ext4_map_blocks(handle, inode, &map,
- EXT4_GET_BLOCKS_CREATE_ZERO);
+ /*
+ * We can avoid zeroing for aligned DAX writes beyond EOF. Other
+ * writes need zeroing either because they can race with page
+ * faults or because they use partial blocks.
+ */
+ flags = EXT4_GET_BLOCKS_PRE_IO | EXT4_GET_BLOCKS_CREATE;
+ if (round_down(offset, 1<<inode->i_blkbits) < inode->i_size ||
+ !ext4_aligned_io(inode, offset, length))
+ flags |= EXT4_GET_BLOCKS_ZERO;
+ ret = ext4_map_blocks(handle, inode, &map, flags);
if (ret < 0) {
ext4_journal_stop(handle);
if (ret == -ENOSPC &&
