Re: [PATCH 0/7] Reduce GFP_ATOMIC allocation failures, candidate fix V3

[Chris Mason <chris.mason@oracle.com>]

On Thu, Nov 12, 2009 at 05:00:05PM -0500, Chris Mason wrote:

[ ...]

> 
> The punch line is that the btrfs guy thinks we can solve all of this with
> just one more thread.  If we change dm-crypt to have a thread dedicated
> to sync IO and a thread dedicated to async IO the system should smooth
> out.

This is pretty likely to set your dm data on fire.  It's only for Mel
who starts his script w/mkfs.

It adds the second thread and more importantly makes sure the kcryptd
thread doesn't get stuck waiting for requests.

-chris

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index ed10381..295ffeb 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -94,6 +94,7 @@ struct crypt_config {
 	struct bio_set *bs;
 
 	struct workqueue_struct *io_queue;
+	struct workqueue_struct *async_io_queue;
 	struct workqueue_struct *crypt_queue;
 
 	/*
@@ -691,7 +692,10 @@ static void kcryptd_queue_io(struct dm_crypt_io *io)
 	struct crypt_config *cc = io->target->private;
 
 	INIT_WORK(&io->work, kcryptd_io);
-	queue_work(cc->io_queue, &io->work);
+	if (io->base_bio->bi_rw & (1 << BIO_RW_SYNCIO))
+		queue_work(cc->io_queue, &io->work);
+	else
+		queue_work(cc->async_io_queue, &io->work);
 }
 
 static void kcryptd_crypt_write_io_submit(struct dm_crypt_io *io,
@@ -759,8 +763,7 @@ static void kcryptd_crypt_write_convert(struct dm_crypt_io *io)
 
 		/* Encryption was already finished, submit io now */
 		if (crypt_finished) {
-			kcryptd_crypt_write_io_submit(io, r, 0);
-
+			kcryptd_crypt_write_io_submit(io, r, 1);
 			/*
 			 * If there was an error, do not try next fragments.
 			 * For async, error is processed in async handler.
@@ -1120,6 +1123,12 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 	} else
 		cc->iv_mode = NULL;
 
+	cc->async_io_queue = create_singlethread_workqueue("kcryptd_async_io");
+	if (!cc->async_io_queue) {
+		ti->error = "Couldn't create kcryptd io queue";
+		goto bad_async_io_queue;
+	}
+
 	cc->io_queue = create_singlethread_workqueue("kcryptd_io");
 	if (!cc->io_queue) {
 		ti->error = "Couldn't create kcryptd io queue";
@@ -1139,6 +1148,8 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 bad_crypt_queue:
 	destroy_workqueue(cc->io_queue);
 bad_io_queue:
+	destroy_workqueue(cc->async_io_queue);
+bad_async_io_queue:
 	kfree(cc->iv_mode);
 bad_ivmode_string:
 	dm_put_device(ti, cc->dev);
@@ -1166,6 +1177,7 @@ static void crypt_dtr(struct dm_target *ti)
 	struct crypt_config *cc = (struct crypt_config *) ti->private;
 
 	destroy_workqueue(cc->io_queue);
+	destroy_workqueue(cc->async_io_queue);
 	destroy_workqueue(cc->crypt_queue);
 
 	if (cc->req)