On 04/29/2016 12:27 PM, Waiman Long wrote:
v4->v5:
- Change patch 1 to disable i_dio_count update in do_dax_io().
v3->v4:
- For patch 1, add the DIO_SKIP_DIO_COUNT flag to dax_do_io() calls
only to address issue raised by Dave Chinner.
v2->v3:
- Remove the percpu_stats helper functions and use percpu_counters
instead.
v1->v2:
- Remove percpu_stats_reset() which is not really needed in this
patchset.
- Move some percpu_stats* functions to the newly created
lib/percpu_stats.c.
- Add a new patch to support 64-bit statistics counts in 32-bit
architectures.
- Rearrange the patches by moving the percpu_stats patches to the
front followed by the ext4 patches.
This patchset aims to improve parallel I/O performance of the ext4
filesystem on DAX.
Patch 1 disables update of the i_dio_count as all DAX I/Os are synchronous
and should be protected from whatever locking was done by the filesystem
caller or within dax_do_io() for read (DIO_LOCKING).
Patch 2 converts some ext4 statistics counts into percpu counts using
the helper functions.
Waiman Long (2):
dax: Don't touch i_dio_count in dax_do_io()
ext4: Make cache hits/misses per-cpu counts
fs/dax.c | 14 ++++++--------
fs/ext4/extents_status.c | 38 +++++++++++++++++++++++++++++---------
fs/ext4/extents_status.h | 4 ++--
3 files changed, 37 insertions(+), 19 deletions(-)
From my testing, it looked like that parallel overwrites to the same
file in an ext4 filesystem on DAX can happen in parallel even if their
range overlaps. It was mainly because the code will drop the i_mutex
before the write. That means the overlapped blocks can get garbage. I
think this is a problem, but I am not expert in the ext4 filesystem to
say for sure. I would like to know your thought on that.
Thanks,
Longman
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