direct-io: only inc/dec inode->i_dio_count for file systems
do_blockdev_direct_IO() increments and decrements the inode
->i_dio_count for each IO operation. It does this to protect against
truncate of a file. Block devices don't need this sort of protection.
For a capable multiqueue setup, this atomic int is the only shared
state between applications accessing the device for O_DIRECT, and it
presents a scaling wall for that. In my testing, as much as 30% of
system time is spent incrementing and decrementing this value. A mixed
read/write workload improved from ~2.5M IOPS to ~9.6M IOPS, with
better latencies too. Before:
clat percentiles (usec):
| 1.00th=[ 33], 5.00th=[ 34], 10.00th=[ 34], 20.00th=[ 34],
| 30.00th=[ 34], 40.00th=[ 34], 50.00th=[ 35], 60.00th=[ 35],
| 70.00th=[ 35], 80.00th=[ 35], 90.00th=[ 37], 95.00th=[ 80],
| 99.00th=[ 98], 99.50th=[ 151], 99.90th=[ 155], 99.95th=[ 155],
| 99.99th=[ 165]
After:
clat percentiles (usec):
| 1.00th=[ 95], 5.00th=[ 108], 10.00th=[ 129], 20.00th=[ 149],
| 30.00th=[ 155], 40.00th=[ 161], 50.00th=[ 167], 60.00th=[ 171],
| 70.00th=[ 177], 80.00th=[ 185], 90.00th=[ 201], 95.00th=[ 270],
| 99.00th=[ 390], 99.50th=[ 398], 99.90th=[ 418], 99.95th=[ 422],
| 99.99th=[ 438]
In other setups, Robert Elliott reported seeing good performance
improvements:
https://lkml.org/lkml/2015/4/3/557
The more applications accessing the device, the worse it gets.
Add a new direct-io flags, DIO_SKIP_DIO_COUNT, which tells
do_blockdev_direct_IO() that it need not worry about incrementing
or decrementing the inode i_dio_count for this caller.
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Elliott, Robert (Server Storage) <elliott@hp.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 79b4fa3..c7e4163 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -152,7 +152,8 @@
struct inode *inode = file->f_mapping->host;
return __blockdev_direct_IO(iocb, inode, I_BDEV(inode), iter, offset,
- blkdev_get_block, NULL, NULL, 0);
+ blkdev_get_block, NULL, NULL,
+ DIO_SKIP_DIO_COUNT);
}
int __sync_blockdev(struct block_device *bdev, int wait)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 8115763..9b774a0 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8129,7 +8129,7 @@
if (check_direct_IO(BTRFS_I(inode)->root, iocb, iter, offset))
return 0;
- atomic_inc(&inode->i_dio_count);
+ inode_dio_begin(inode);
smp_mb__after_atomic();
/*
@@ -8169,7 +8169,7 @@
current->journal_info = &outstanding_extents;
} else if (test_bit(BTRFS_INODE_READDIO_NEED_LOCK,
&BTRFS_I(inode)->runtime_flags)) {
- inode_dio_done(inode);
+ inode_dio_end(inode);
flags = DIO_LOCKING | DIO_SKIP_HOLES;
wakeup = false;
}
@@ -8188,7 +8188,7 @@
}
out:
if (wakeup)
- inode_dio_done(inode);
+ inode_dio_end(inode);
if (relock)
mutex_lock(&inode->i_mutex);
diff --git a/fs/dax.c b/fs/dax.c
index a278469..cdde2b3 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -209,7 +209,7 @@
}
/* Protects against truncate */
- atomic_inc(&inode->i_dio_count);
+ inode_dio_begin(inode);
retval = dax_io(inode, iter, pos, end, get_block, &bh);
@@ -219,7 +219,7 @@
if ((retval > 0) && end_io)
end_io(iocb, pos, retval, bh.b_private);
- inode_dio_done(inode);
+ inode_dio_end(inode);
out:
return retval;
}
diff --git a/fs/direct-io.c b/fs/direct-io.c
index c3b560b..745d234 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -253,7 +253,9 @@
if (dio->end_io && dio->result)
dio->end_io(dio->iocb, offset, transferred, dio->private);
- inode_dio_done(dio->inode);
+ if (!(dio->flags & DIO_SKIP_DIO_COUNT))
+ inode_dio_end(dio->inode);
+
if (is_async) {
if (dio->rw & WRITE) {
int err;
@@ -1195,7 +1197,8 @@
/*
* Will be decremented at I/O completion time.
*/
- atomic_inc(&inode->i_dio_count);
+ if (!(dio->flags & DIO_SKIP_DIO_COUNT))
+ inode_dio_begin(inode);
retval = 0;
sdio.blkbits = blkbits;
diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
index 3580629e..9588240 100644
--- a/fs/ext4/indirect.c
+++ b/fs/ext4/indirect.c
@@ -682,11 +682,11 @@
* via ext4_inode_block_unlocked_dio(). Check inode's state
* while holding extra i_dio_count ref.
*/
- atomic_inc(&inode->i_dio_count);
+ inode_dio_begin(inode);
smp_mb();
if (unlikely(ext4_test_inode_state(inode,
EXT4_STATE_DIOREAD_LOCK))) {
- inode_dio_done(inode);
+ inode_dio_end(inode);
goto locked;
}
if (IS_DAX(inode))
@@ -697,7 +697,7 @@
inode->i_sb->s_bdev, iter,
offset, ext4_get_block, NULL,
NULL, 0);
- inode_dio_done(inode);
+ inode_dio_end(inode);
} else {
locked:
if (IS_DAX(inode))
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 063052e..bccec41 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2977,7 +2977,7 @@
* overwrite DIO as i_dio_count needs to be incremented under i_mutex.
*/
if (iov_iter_rw(iter) == WRITE)
- atomic_inc(&inode->i_dio_count);
+ inode_dio_begin(inode);
/* If we do a overwrite dio, i_mutex locking can be released */
overwrite = *((int *)iocb->private);
@@ -3079,7 +3079,7 @@
retake_lock:
if (iov_iter_rw(iter) == WRITE)
- inode_dio_done(inode);
+ inode_dio_end(inode);
/* take i_mutex locking again if we do a ovewrite dio */
if (overwrite) {
up_read(&EXT4_I(inode)->i_data_sem);
diff --git a/fs/inode.c b/fs/inode.c
index 94886f9..ea37cd1 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1946,20 +1946,6 @@
EXPORT_SYMBOL(inode_dio_wait);
/*
- * inode_dio_done - signal finish of a direct I/O requests
- * @inode: inode the direct I/O happens on
- *
- * This is called once we've finished processing a direct I/O request,
- * and is used to wake up callers waiting for direct I/O to be quiesced.
- */
-void inode_dio_done(struct inode *inode)
-{
- if (atomic_dec_and_test(&inode->i_dio_count))
- wake_up_bit(&inode->i_state, __I_DIO_WAKEUP);
-}
-EXPORT_SYMBOL(inode_dio_done);
-
-/*
* inode_set_flags - atomically set some inode flags
*
* Note: the caller should be holding i_mutex, or else be sure that
diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index ed0e603..b2cbc3a 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -386,7 +386,7 @@
if (write)
nfs_zap_mapping(inode, inode->i_mapping);
- inode_dio_done(inode);
+ inode_dio_end(inode);
if (dreq->iocb) {
long res = (long) dreq->error;
@@ -486,7 +486,7 @@
&nfs_direct_read_completion_ops);
get_dreq(dreq);
desc.pg_dreq = dreq;
- atomic_inc(&inode->i_dio_count);
+ inode_dio_begin(inode);
while (iov_iter_count(iter)) {
struct page **pagevec;
@@ -538,7 +538,7 @@
* generic layer handle the completion.
*/
if (requested_bytes == 0) {
- inode_dio_done(inode);
+ inode_dio_end(inode);
nfs_direct_req_release(dreq);
return result < 0 ? result : -EIO;
}
@@ -872,7 +872,7 @@
&nfs_direct_write_completion_ops);
desc.pg_dreq = dreq;
get_dreq(dreq);
- atomic_inc(&inode->i_dio_count);
+ inode_dio_begin(inode);
NFS_I(inode)->write_io += iov_iter_count(iter);
while (iov_iter_count(iter)) {
@@ -928,7 +928,7 @@
* generic layer handle the completion.
*/
if (requested_bytes == 0) {
- inode_dio_done(inode);
+ inode_dio_end(inode);
nfs_direct_req_release(dreq);
return result < 0 ? result : -EIO;
}