[PATCH 1/3] dax: Take shared lock in dax_do_io()
From: Waiman Long <hidden>
Date: 2016-06-03 22:28:40
Also in:
lkml
Subsystem:
filesystem direct access (dax), filesystems (vfs and infrastructure), the rest · Maintainers:
Dan Williams, Alexander Viro, Christian Brauner, Linus Torvalds
With the change from i_mutex to i_rwsem in 4.7 kernel, the locking scheme in dax_do_io() can now be changed to take a shared lock for read so that multiple readers can access the same file concurrently. With a 38-threads fio I/O test with 2 shared files (on DAX-mount, ext4 formatted NVDIMM) running on a 4-socket Haswell-EX server with 4.7-rc1 kernel, the aggregated bandwidths before and after the patch were: Test W/O patch With patch % change ---- --------- ---------- -------- Read-only 4711MB/s 16031MB/s +240% Read-write 1932MB/s 1040MB/s -46% There was a big increase in parallel read performance. However, parallel read-write test showed a regression because a mix of readers and writers will largely disable optimistic spinning. Signed-off-by: Waiman Long <redacted> --- fs/dax.c | 9 +++++---- 1 files changed, 5 insertions(+), 4 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c
index 761495b..ff57d88 100644
--- a/fs/dax.c
+++ b/fs/dax.c@@ -247,8 +247,8 @@ static ssize_t dax_io(struct inode *inode, struct iov_iter *iter, * @flags: See below * * This function uses the same locking scheme as do_blockdev_direct_IO: - * If @flags has DIO_LOCKING set, we assume that the i_mutex is held by the - * caller for writes. For reads, we take and release the i_mutex ourselves. + * If @flags has DIO_LOCKING set, we assume that the i_rwsem is held by the + * caller for writes. For reads, we take and release the i_rwsem ourselves. * If DIO_LOCKING is not set, the filesystem takes care of its own locking. * As with do_blockdev_direct_IO(), we increment i_dio_count while the I/O * is in progress.
@@ -265,8 +265,9 @@ ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode, memset(&bh, 0, sizeof(bh)); bh.b_bdev = inode->i_sb->s_bdev; + /* Take the shared lock for read */ if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ) - inode_lock(inode); + inode_lock_shared(inode); /* Protects against truncate */ if (!(flags & DIO_SKIP_DIO_COUNT))
@@ -275,7 +276,7 @@ ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode, retval = dax_io(inode, iter, pos, end, get_block, &bh); if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ) - inode_unlock(inode); + inode_unlock_shared(inode); if (end_io) { int err;
--
1.7.1