On 8/20/20 6:23 PM, Jan Kara wrote:
On Thu 20-08-20 17:06:28, Ritesh Harjani wrote:Currently in case of DAX, we are starting a transaction everytime for IOMAP_WRITE case. This can be optimized away in case of an overwrite (where the blocks were already allocated). This could give a significant performance boost for multi-threaded random writes. Reported-by: Dan Williams <dan.j.williams@xxxxxxxxx> Signed-off-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>Thanks for returning to this and I'm glad to see how much this helped :) BTW, I'd suspect there could be also significant contention and cache line bouncing on j_state_lock and transaction's atomic counters...
ok, will try and profile to see if this happens.
--- fs/ext4/ext4.h | 1 + fs/ext4/file.c | 2 +- fs/ext4/inode.c | 8 +++++++- 3 files changed, 9 insertions(+), 2 deletions(-) diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 42f5060f3cdf..9a2138afc751 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -3232,6 +3232,7 @@ extern const struct dentry_operations ext4_dentry_ops; extern const struct inode_operations ext4_file_inode_operations; extern const struct file_operations ext4_file_operations; extern loff_t ext4_llseek(struct file *file, loff_t offset, int origin); +extern bool ext4_overwrite_io(struct inode *inode, loff_t pos, loff_t len);/* inline.c */extern int ext4_get_max_inline_size(struct inode *inode); diff --git a/fs/ext4/file.c b/fs/ext4/file.c index 2a01e31a032c..51cd92ac1758 100644 --- a/fs/ext4/file.c +++ b/fs/ext4/file.c @@ -188,7 +188,7 @@ ext4_extending_io(struct inode *inode, loff_t offset, size_t len) }/* Is IO overwriting allocated and initialized blocks? */-static bool ext4_overwrite_io(struct inode *inode, loff_t pos, loff_t len) +bool ext4_overwrite_io(struct inode *inode, loff_t pos, loff_t len) { struct ext4_map_blocks map; unsigned int blkbits = inode->i_blkbits; diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 10dd470876b3..f0ac0ee9e991 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 ret; struct ext4_map_blocks map; u8 blkbits = inode->i_blkbits; + bool overwrite = false;if ((offset >> blkbits) > EXT4_MAX_LOGICAL_BLOCK)return -EINVAL; @@ -3430,6 +3431,9 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length, if (WARN_ON_ONCE(ext4_has_inline_data(inode))) return -ERANGE;+ if (IS_DAX(inode) && (flags & IOMAP_WRITE) &&+ ext4_overwrite_io(inode, offset, length)) + overwrite = true;So the patch looks correct but using ext4_overwrite_io() seems a bit foolish since under the hood it does ext4_map_blocks() only to be able to decide whether to call ext4_map_blocks() once again with exactly the same arguments :). So I'd rather slightly refactor the code in ext4_iomap_begin() to avoid this double calling of ext4_map_blocks() for the fast path.
Yes, agreed. Looking at the numbers I was excited to post out the RFC for discussion. Will make above changes and post. :) With DIO, we need to detect overwrite case early in ext4_dio_write_iter() to determine whether we need shared or excl. locks - so probably for DIO case we still need overwrite check in ext4_dio_write_iter() Thanks for review!! -ritesh
Honza/* * Calculate the first and last logical blocks respectively. */ @@ -3437,13 +3441,15 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length, map.m_len = min_t(loff_t, (offset + length - 1) >> blkbits, EXT4_MAX_LOGICAL_BLOCK) - map.m_lblk + 1;- if (flags & IOMAP_WRITE)+ if ((flags & IOMAP_WRITE) && !overwrite) ret = ext4_iomap_alloc(inode, &map, flags); else ret = ext4_map_blocks(NULL, inode, &map, 0);if (ret < 0)return ret; + if (IS_DAX(inode) && overwrite) + WARN_ON(!(map.m_flags & EXT4_MAP_MAPPED));ext4_set_iomap(inode, iomap, &map, offset, length); --2.25.4
