[dm-devel] [PATCH] dm-writecache: back off if the kcopyd workqueue is blocked

[Mikulas Patocka <mpatocka@redhat.com>]

This patch makes dm-writecache wait if the kcopyd workqueue is blocked (it 
happens when one of the devices is contested). It improves performance of 
"mkfs.ext2" by approximatelly 20%.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

Index: linux/drivers/md/dm-kcopyd.c
===================================================================
--- linux.orig/drivers/md/dm-kcopyd.c
+++ linux/drivers/md/dm-kcopyd.c
@@ -888,6 +888,12 @@ void dm_kcopyd_do_callback(void *j, int
 }
 EXPORT_SYMBOL(dm_kcopyd_do_callback);
 
+void dm_kcopyd_wait_if_busy(struct dm_kcopyd_client *kc)
+{
+	flush_workqueue(kc->kcopyd_wq);
+}
+EXPORT_SYMBOL(dm_kcopyd_wait_if_busy);
+
 /*
  * Cancels a kcopyd job, eg. someone might be deactivating a
  * mirror.
Index: linux/drivers/md/dm-writecache.c
===================================================================
--- linux.orig/drivers/md/dm-writecache.c
+++ linux/drivers/md/dm-writecache.c
@@ -1819,6 +1819,9 @@ static void writecache_writeback(struct
 	struct writeback_list wbl;
 	unsigned long n_walked;
 
+	if (!WC_MODE_PMEM(wc))
+		dm_kcopyd_wait_if_busy(wc->dm_kcopyd);
+
 	wc_lock(wc);
 restart:
 	if (writecache_has_error(wc)) {
Index: linux/include/linux/dm-kcopyd.h
===================================================================
--- linux.orig/include/linux/dm-kcopyd.h
+++ linux/include/linux/dm-kcopyd.h
@@ -81,6 +81,8 @@ void *dm_kcopyd_prepare_callback(struct
 				 dm_kcopyd_notify_fn fn, void *context);
 void dm_kcopyd_do_callback(void *job, int read_err, unsigned long write_err);
 
+void dm_kcopyd_wait_if_busy(struct dm_kcopyd_client *kc);
+
 void dm_kcopyd_zero(struct dm_kcopyd_client *kc,
 		    unsigned num_dests, struct dm_io_region *dests,
 		    unsigned flags, dm_kcopyd_notify_fn fn, void *context);

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