From: Steven Whitehouse <swhiteho@redhat.com>
Subject: [RHEL 5.1] Shrink size of struct gdlm_lock (bz #240013)
Date: Thu, 31 May 2007 09:54:25 +0100
Bugzilla: 240013
Message-Id: <1180601665.25918.73.camel@quoit>
Changelog: [gfs2] Shrink size of struct gdlm_lock


Hi,

This patch is taken from the upstream GFS2 git tree where it has been
for a little while. It shrinks the size of struct gdlm_lock by 32 bytes
(on x86_64) which is well worth doing when there can be potentially
millions of these structures in use at one time. Its been tested as part
of the upstream kernel code and fixes bz #240013.

Steve.

------------------------------------------------------------------------------------
X-Git-Url: http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Fsteve%2Fgfs2-2.6-nmw.git;a=commitdiff_plain;h=43abbfe7597ad85c9096859fc85190bb73938fe6

[GFS2] Reduce size of struct gdlm_lock

This patch removes the completion (which is rather large) from struct
gdlm_lock in favour of using the wait_on_bit() functions. We don't need
to add any extra fields to the structure to do this, so we save 32 bytes
(on x86_64) per structure. This adds up to quite a lot when we may
potentially have millions of these lock structures,

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Acked-by: David Teigland <teigland@redhat.com>
---

diff --git a/fs/gfs2/locking/dlm/lock.c b/fs/gfs2/locking/dlm/lock.c
index c305255..542a797 100644
--- a/fs/gfs2/locking/dlm/lock.c
+++ b/fs/gfs2/locking/dlm/lock.c
@@ -174,7 +174,6 @@ static int gdlm_create_lp(struct gdlm_ls *ls, struct lm_lockname *name,
 	lp->cur = DLM_LOCK_IV;
 	lp->lvb = NULL;
 	lp->hold_null = NULL;
-	init_completion(&lp->ast_wait);
 	INIT_LIST_HEAD(&lp->clist);
 	INIT_LIST_HEAD(&lp->blist);
 	INIT_LIST_HEAD(&lp->delay_list);
@@ -399,6 +398,12 @@ static void gdlm_del_lvb(struct gdlm_lock *lp)
 	lp->lksb.sb_lvbptr = NULL;
 }
 
+static int gdlm_ast_wait(void *word)
+{
+	schedule();
+	return 0;
+}
+
 /* This can do a synchronous dlm request (requiring a lock_dlm thread to get
    the completion) because gfs won't call hold_lvb() during a callback (from
    the context of a lock_dlm thread). */
@@ -424,10 +429,10 @@ static int hold_null_lock(struct gdlm_lock *lp)
 	lpn->lkf = DLM_LKF_VALBLK | DLM_LKF_EXPEDITE;
 	set_bit(LFL_NOBAST, &lpn->flags);
 	set_bit(LFL_INLOCK, &lpn->flags);
+	set_bit(LFL_AST_WAIT, &lpn->flags);
 
-	init_completion(&lpn->ast_wait);
 	gdlm_do_lock(lpn);
-	wait_for_completion(&lpn->ast_wait);
+	wait_on_bit(&lpn->flags, LFL_AST_WAIT, gdlm_ast_wait, TASK_UNINTERRUPTIBLE);
 	error = lpn->lksb.sb_status;
 	if (error) {
 		printk(KERN_INFO "lock_dlm: hold_null_lock dlm error %d\n",
diff --git a/fs/gfs2/locking/dlm/lock_dlm.h b/fs/gfs2/locking/dlm/lock_dlm.h
index d074c6e..24d70f7 100644
--- a/fs/gfs2/locking/dlm/lock_dlm.h
+++ b/fs/gfs2/locking/dlm/lock_dlm.h
@@ -101,6 +101,7 @@ enum {
 	LFL_NOBAST		= 10,
 	LFL_HEADQUE		= 11,
 	LFL_UNLOCK_DELETE	= 12,
+	LFL_AST_WAIT		= 13,
 };
 
 struct gdlm_lock {
@@ -117,7 +118,6 @@ struct gdlm_lock {
 	unsigned long		flags;		/* lock_dlm flags LFL_ */
 
 	int			bast_mode;	/* protected by async_lock */
-	struct completion	ast_wait;
 
 	struct list_head	clist;		/* complete */
 	struct list_head	blist;		/* blocking */
diff --git a/fs/gfs2/locking/dlm/thread.c b/fs/gfs2/locking/dlm/thread.c
index 9cf1f16..1aca51e 100644
--- a/fs/gfs2/locking/dlm/thread.c
+++ b/fs/gfs2/locking/dlm/thread.c
@@ -44,6 +44,13 @@ static void process_blocking(struct gdlm_lock *lp, int bast_mode)
 	ls->fscb(ls->sdp, cb, &lp->lockname);
 }
 
+static void wake_up_ast(struct gdlm_lock *lp)
+{
+	clear_bit(LFL_AST_WAIT, &lp->flags);
+	smp_mb__after_clear_bit();
+	wake_up_bit(&lp->flags, LFL_AST_WAIT);
+}
+
 static void process_complete(struct gdlm_lock *lp)
 {
 	struct gdlm_ls *ls = lp->ls;
@@ -136,7 +143,7 @@ static void process_complete(struct gdlm_lock *lp)
 	 */
 
 	if (test_and_clear_bit(LFL_SYNC_LVB, &lp->flags)) {
-		complete(&lp->ast_wait);
+		wake_up_ast(lp);
 		return;
 	}
 
@@ -214,7 +221,7 @@ out:
 	if (test_bit(LFL_INLOCK, &lp->flags)) {
 		clear_bit(LFL_NOBLOCK, &lp->flags);
 		lp->cur = lp->req;
-		complete(&lp->ast_wait);
+		wake_up_ast(lp);
 		return;
 	}