[Cluster-devel] [DLM PATCH] DLM: Don't wait for resource library lookups if NOLOOKUP is specified

[Bob Peterson]

Hi,

This patch adds a new lock flag, DLM_LKF_NOLOOKUP, which instructs DLM
to refrain from sending lookup requests in cases where the lock library
node is not the current node. This is similar to the DLM_LKF_NOQUEUE
flag, except it fails locks that would require a lookup, with -EAGAIN.

This is not just about saving a network operation. It allows callers
like GFS2 to master locks for which they are the directory node. Each
node can then "prefer" local locks, especially in the case of GFS2
selecting resource groups for block allocations (implemented with a
separate patch). This mastering of local locks distributes the locks
between the nodes (at least until nodes enter or leave the cluster),
which tends to make each node "keep to itself" when doing allocations.
Thus, dlm communications are kept to a minimum, which results in
significantly faster block allocations.

Regards,

Bob Peterson
Red Hat File Systems

Signed-off-by: Bob Peterson <rpeterso at redhat.com> 
---
 fs/dlm/lock.c                     | 16 ++++++++++++++--
 include/uapi/linux/dlmconstants.h |  7 +++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/fs/dlm/lock.c b/fs/dlm/lock.c
index 83f3d55..f1e5b04 100644
--- a/fs/dlm/lock.c
+++ b/fs/dlm/lock.c
@@ -222,6 +222,11 @@ static inline int can_be_queued(struct dlm_lkb *lkb)
 	return !(lkb->lkb_exflags & DLM_LKF_NOQUEUE);
 }
 
+static inline int can_be_looked_up(struct dlm_lkb *lkb)
+{
+	return !(lkb->lkb_exflags & DLM_LKF_NOLOOKUP);
+}
+
 static inline int force_blocking_asts(struct dlm_lkb *lkb)
 {
 	return (lkb->lkb_exflags & DLM_LKF_NOQUEUEBAST);
@@ -2745,6 +2750,11 @@ static int set_master(struct dlm_rsb *r, struct dlm_lkb *lkb)
 		return 0;
 	}
 
+	if (!can_be_looked_up(lkb)) {
+		queue_cast(r, lkb, -EAGAIN);
+		return -EAGAIN;
+	}
+
 	wait_pending_remove(r);
 
 	r->res_first_lkid = lkb->lkb_id;
@@ -2828,7 +2838,8 @@ static int set_lock_args(int mode, struct dlm_lksb *lksb, uint32_t flags,
 	if (flags & DLM_LKF_CONVDEADLK && !(flags & DLM_LKF_CONVERT))
 		goto out;
 
-	if (flags & DLM_LKF_CONVDEADLK && flags & DLM_LKF_NOQUEUE)
+	if (flags & DLM_LKF_CONVDEADLK && (flags & (DLM_LKF_NOQUEUE |
+						    DLM_LKF_NOLOOKUP)))
 		goto out;
 
 	if (flags & DLM_LKF_EXPEDITE && flags & DLM_LKF_CONVERT)
@@ -2837,7 +2848,8 @@ static int set_lock_args(int mode, struct dlm_lksb *lksb, uint32_t flags,
 	if (flags & DLM_LKF_EXPEDITE && flags & DLM_LKF_QUECVT)
 		goto out;
 
-	if (flags & DLM_LKF_EXPEDITE && flags & DLM_LKF_NOQUEUE)
+	if (flags & DLM_LKF_EXPEDITE && (flags & (DLM_LKF_NOQUEUE |
+						  DLM_LKF_NOLOOKUP)))
 		goto out;
 
 	if (flags & DLM_LKF_EXPEDITE && mode != DLM_LOCK_NL)
diff --git a/include/uapi/linux/dlmconstants.h b/include/uapi/linux/dlmconstants.h
index 47bf08d..4b9ba15 100644
--- a/include/uapi/linux/dlmconstants.h
+++ b/include/uapi/linux/dlmconstants.h
@@ -131,6 +131,12 @@
  * Unlock the lock even if it is converting or waiting or has sublocks.
  * Only really for use by the userland device.c code.
  *
+ * DLM_LKF_NOLOOKUP
+ *
+ * Don't take any network time/bandwidth to do directory owner lookups.
+ * This is a lock for which we only care whether it's completely under
+ * local jurisdiction.
+ *
  */
 
 #define DLM_LKF_NOQUEUE		0x00000001
@@ -152,6 +158,7 @@
 #define DLM_LKF_ALTCW		0x00010000
 #define DLM_LKF_FORCEUNLOCK	0x00020000
 #define DLM_LKF_TIMEOUT		0x00040000
+#define DLM_LKF_NOLOOKUP	0x00080000
 
 /*
  * Some return codes that are not in errno.h