LU-11199 mdt: Attempt lookup lock on open

Commit 4f50273a (LU-10269 ldlm: fix the issues introduced
by try bits) changed the locking behavior on open to not
attempt to grant the LOOKUP lock bit.  This causes a
performance regression in open(), which is up to 75% in
some benchmarks, such as mdsrate (from lustre/tests/mpi):

First create the files:
mpirun -n 4 /usr/lib64/lustre/tests/mdsrate /
-d /mnt/lustre/mdsrate --create --nfile=30000

Then drop caches:
echo 3 > /proc/sys/vm/drop_caches

Then run the open benchmark:
mpirun -n 4 /usr/lib64/lustre/tests/mdsrate /
-d /mnt/lustre/mdsrate --open --iters 8000 --nfile=30000
[More details in LU-1199]

This patch reverts that specific part of 4f50273a, which
restores open() performance to prior levels.

It may not be 100% correct to ask for open only when
also asking for layout, but this is the earlier behavior.

There is a further patch in flight to optimize this
code:
https://review.whamcloud.com/32156

And further changes are left for that patch.

Cray-bug-id: LUS-6358

Change-Id: Iceca88807e99955f28eba6bbcb3585964f7df2f4
Signed-off-by: Patrick Farrell <paf@cray.com>
Reviewed-on: https://review.whamcloud.com/32929
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>

diff --git a/lustre/mdt/mdt_open.c b/lustre/mdt/mdt_open.c
index cc0faf9..28d0656 100644 (file)
--- a/lustre/mdt/mdt_open.c
+++ b/lustre/mdt/mdt_open.c
@@ -909,9 +909,15 @@ static int mdt_object_open_lock(struct mdt_thread_info *info,
 
        mdt_lock_reg_init(lhc, lm);
 
-       /* one problem to return layout lock on open is that it may result
-        * in too many layout locks cached on the client side. */
+       /* Return lookup lock to validate inode at the client side.
+        * This is pretty important otherwise MDT will return layout
+        * lock for each open.
+        * However this is a double-edged sword because changing
+        * permission will revoke a huge number of LOOKUP locks.
+        */
        if (!OBD_FAIL_CHECK(OBD_FAIL_MDS_NO_LL_OPEN) && try_layout) {
+               if (!(*ibits & MDS_INODELOCK_LOOKUP))
+                       trybits |= MDS_INODELOCK_LOOKUP;
                trybits |= MDS_INODELOCK_LAYOUT;
        }