md/raid5: For odirect-write performance, do not set STRIPE_PREREAD_ACTIVE.

'sync' writes set both REQ_SYNC and REQ_NOIDLE.
O_DIRECT writes set REQ_SYNC but not REQ_NOIDLE.

We currently assume that a REQ_SYNC request will not be followed by
more requests and so set STRIPE_PREREAD_ACTIVE to expedite the
request.
This is appropriate for sync requests, but not for O_DIRECT requests.

So make the setting of STRIPE_PREREAD_ACTIVE conditional on REQ_NOIDLE
rather than REQ_SYNC.  This is consistent with the documented meaning
of REQ_NOIDLE:

        __REQ_NOIDLE,           /* don't anticipate more IO after this one */

Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 29493982dbf5561ba5b2f0d9467bc12774cba2e9..259f519814ca0f083696d875dc16fdc4bd141659 100644 (file)
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -4135,7 +4135,7 @@ static void make_request(struct mddev *mddev, struct bio * bi)
                        finish_wait(&conf->wait_for_overlap, &w);
                        set_bit(STRIPE_HANDLE, &sh->state);
                        clear_bit(STRIPE_DELAYED, &sh->state);
-                       if ((bi->bi_rw & REQ_SYNC) &&
+                       if ((bi->bi_rw & REQ_NOIDLE) &&
                            !test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
                                atomic_inc(&conf->preread_active_stripes);
                        mddev_check_plugged(mddev);