[PATCH] backing-dev: use synchronize_rcu_expedited instead ofsynchronize_rcu

[Mikulas Patocka]

Hi Jens

Please would you consider taking this into the block tree? It seems to 
speed up device deletion enormously.

Mikulas

---

backing-dev: use synchronize_rcu_expedited instead of synchronize_rcu

synchronize_rcu sleeps several timer ticks. synchronize_rcu_expedited is 
much faster.

With 100Hz timer frequency, when we remove 10000 block devices with 
"dmsetup remove_all" command, it takes 27 minutes. With this patch, 
removing 10000 block devices takes only 15 seconds.

Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>

---
 mm/backing-dev.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-3.0-rc7-fast/mm/backing-dev.c
===================================================================
--- linux-3.0-rc7-fast.orig/mm/backing-dev.c	2011-07-19 18:01:00.000000000 +0200
+++ linux-3.0-rc7-fast/mm/backing-dev.c	2011-07-19 18:01:07.000000000 +0200
@@ -505,7 +505,7 @@ static void bdi_remove_from_list(struct 
 	list_del_rcu(&bdi->bdi_list);
 	spin_unlock_bh(&bdi_lock);
 
-	synchronize_rcu();
+	synchronize_rcu_expedited();
 }
 
 int bdi_register(struct backing_dev_info *bdi, struct device *parent,
--
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