[PATCH v2 0/6] fuse: process direct IO asynchronously

["Maxim V. Patlasov" <MPatlasov@parallels.com>]

Hi,

Existing fuse implementation always processes direct IO synchronously: it
submits next request to userspace fuse only when previous is completed. This
is suboptimal because: 1) libaio DIO works in blocking way; 2) userspace fuse
can't achieve parallelism  processing several requests simultaneously (e.g.
in case of distributed network storage); 3) userspace fuse can't merge
requests before passing it to actual storage.

The idea of the patch-set is to submit fuse requests in non-blocking way
(where it's possible) and either return -EIOCBQUEUED or wait for their
completion synchronously. The patch-set to be applied on top of for-next of
Miklos' git repo.

To estimate performance improvement I used slightly modified fusexmp over
tmpfs (clearing O_DIRECT bit from fi->flags in xmp_open). For synchronous
operations I used 'dd' like this:

dd of=/dev/null if=/fuse/mnt/file bs=2M count=256 iflag=direct
dd if=/dev/zero of=/fuse/mnt/file bs=2M count=256 oflag=direct conv=notrunc

For AIO I used 'aio-stress' like this:

aio-stress -s 512 -a 4 -b 1 -c 1 -O -o 1 /fuse/mnt/file
aio-stress -s 512 -a 4 -b 1 -c 1 -O -o 0 /fuse/mnt/file

The throughput on some commodity (rather feeble) server was (in MB/sec):

             original / patched

dd reads:    ~322     / ~382
dd writes:   ~277     / ~288

aio reads:   ~380     / ~459
aio writes:  ~319     / ~353

Changed in v2 - cleanups suggested by Brian:
 - Updated fuse_io_priv with an async field and file pointer to preserve
   the current style of interface (i.e., use this instead of iocb).
 - Trigger the type of request submission based on the async field.
 - Pulled up the fuse_write_update_size() call out of __fuse_direct_write()
   to make the separate paths more consistent.

Thanks,
Maxim

---

Maxim V. Patlasov (6):
      fuse: move fuse_release_user_pages() up
      fuse: add support of async IO
      fuse: make fuse_direct_io() aware about AIO
      fuse: enable asynchronous processing direct IO
      fuse: truncate file if async dio failed
      fuse: optimize short direct reads


 fs/fuse/cuse.c   |    6 +
 fs/fuse/file.c   |  290 +++++++++++++++++++++++++++++++++++++++++++++++-------
 fs/fuse/fuse_i.h |   19 +++-
 3 files changed, 276 insertions(+), 39 deletions(-)

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