dm crypt: offload writes to thread

Submitting write bios directly in the encryption thread caused serious
performance degradation.  On a multiprocessor machine, encryption requests
finish in a different order than they were submitted.  Consequently, write
requests would be submitted in a different order and it could cause severe
performance degradation.

Move the submission of write requests to a separate thread so that the
requests can be sorted before submitting.  But this commit improves
dm-crypt performance even without having dm-crypt perform request
sorting (in particular it enables IO schedulers like CFQ to sort more
effectively).

Note: it is required that a previous commit ("dm crypt: don't allocate
pages for a partial request") be applied before applying this patch.
Otherwise, this commit could introduce a crash.

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

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index c29daf4..8c0e36b 100644 (file)
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -18,6 +18,7 @@
 #include <linux/slab.h>
 #include <linux/crypto.h>
 #include <linux/workqueue.h>
+#include <linux/kthread.h>
 #include <linux/backing-dev.h>
 #include <linux/atomic.h>
 #include <linux/scatterlist.h>
@@ -58,6 +59,8 @@ struct dm_crypt_io {
        atomic_t io_pending;
        int error;
        sector_t sector;
+
+       struct list_head list;
 } CRYPTO_MINALIGN_ATTR;
 
 struct dm_crypt_request {
@@ -128,6 +131,10 @@ struct crypt_config {
        struct workqueue_struct *io_queue;
        struct workqueue_struct *crypt_queue;
 
+       struct task_struct *write_thread;
+       wait_queue_head_t write_thread_wait;
+       struct list_head write_thread_list;
+
        char *cipher;
        char *cipher_string;
 
@@ -1136,37 +1143,89 @@ static int kcryptd_io_read(struct dm_crypt_io *io, gfp_t gfp)
        return 0;
 }
 
+static void kcryptd_io_read_work(struct work_struct *work)
+{
+       struct dm_crypt_io *io = container_of(work, struct dm_crypt_io, work);
+
+       crypt_inc_pending(io);
+       if (kcryptd_io_read(io, GFP_NOIO))
+               io->error = -ENOMEM;
+       crypt_dec_pending(io);
+}
+
+static void kcryptd_queue_read(struct dm_crypt_io *io)
+{
+       struct crypt_config *cc = io->cc;
+
+       INIT_WORK(&io->work, kcryptd_io_read_work);
+       queue_work(cc->io_queue, &io->work);
+}
+
 static void kcryptd_io_write(struct dm_crypt_io *io)
 {
        struct bio *clone = io->ctx.bio_out;
+
        generic_make_request(clone);
 }
 
-static void kcryptd_io(struct work_struct *work)
+static int dmcrypt_write(void *data)
 {
-       struct dm_crypt_io *io = container_of(work, struct dm_crypt_io, work);
+       struct crypt_config *cc = data;
+       while (1) {
+               struct list_head local_list;
+               struct blk_plug plug;
 
-       if (bio_data_dir(io->base_bio) == READ) {
-               crypt_inc_pending(io);
-               if (kcryptd_io_read(io, GFP_NOIO))
-                       io->error = -ENOMEM;
-               crypt_dec_pending(io);
-       } else
-               kcryptd_io_write(io);
-}
+               DECLARE_WAITQUEUE(wait, current);
 
-static void kcryptd_queue_io(struct dm_crypt_io *io)
-{
-       struct crypt_config *cc = io->cc;
+               spin_lock_irq(&cc->write_thread_wait.lock);
+continue_locked:
 
-       INIT_WORK(&io->work, kcryptd_io);
-       queue_work(cc->io_queue, &io->work);
+               if (!list_empty(&cc->write_thread_list))
+                       goto pop_from_list;
+
+               __set_current_state(TASK_INTERRUPTIBLE);
+               __add_wait_queue(&cc->write_thread_wait, &wait);
+
+               spin_unlock_irq(&cc->write_thread_wait.lock);
+
+               if (unlikely(kthread_should_stop())) {
+                       set_task_state(current, TASK_RUNNING);
+                       remove_wait_queue(&cc->write_thread_wait, &wait);
+                       break;
+               }
+
+               schedule();
+
+               set_task_state(current, TASK_RUNNING);
+               spin_lock_irq(&cc->write_thread_wait.lock);
+               __remove_wait_queue(&cc->write_thread_wait, &wait);
+               goto continue_locked;
+
+pop_from_list:
+               local_list = cc->write_thread_list;
+               local_list.next->prev = &local_list;
+               local_list.prev->next = &local_list;
+               INIT_LIST_HEAD(&cc->write_thread_list);
+
+               spin_unlock_irq(&cc->write_thread_wait.lock);
+
+               blk_start_plug(&plug);
+               do {
+                       struct dm_crypt_io *io = container_of(local_list.next,
+                                               struct dm_crypt_io, list);
+                       list_del(&io->list);
+                       kcryptd_io_write(io);
+               } while (!list_empty(&local_list));
+               blk_finish_plug(&plug);
+       }
+       return 0;
 }
 
 static void kcryptd_crypt_write_io_submit(struct dm_crypt_io *io, int async)
 {
        struct bio *clone = io->ctx.bio_out;
        struct crypt_config *cc = io->cc;
+       unsigned long flags;
 
        if (unlikely(io->error < 0)) {
                crypt_free_buffer_pages(cc, clone);
@@ -1180,10 +1239,10 @@ static void kcryptd_crypt_write_io_submit(struct dm_crypt_io *io, int async)
 
        clone->bi_iter.bi_sector = cc->start + io->sector;
 
-       if (async)
-               kcryptd_queue_io(io);
-       else
-               generic_make_request(clone);
+       spin_lock_irqsave(&cc->write_thread_wait.lock, flags);
+       list_add_tail(&io->list, &cc->write_thread_list);
+       wake_up_locked(&cc->write_thread_wait);
+       spin_unlock_irqrestore(&cc->write_thread_wait.lock, flags);
 }
 
 static void kcryptd_crypt_write_convert(struct dm_crypt_io *io)
@@ -1426,6 +1485,9 @@ static void crypt_dtr(struct dm_target *ti)
        if (!cc)
                return;
 
+       if (cc->write_thread)
+               kthread_stop(cc->write_thread);
+
        if (cc->io_queue)
                destroy_workqueue(cc->io_queue);
        if (cc->crypt_queue)
@@ -1764,6 +1826,18 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
                goto bad;
        }
 
+       init_waitqueue_head(&cc->write_thread_wait);
+       INIT_LIST_HEAD(&cc->write_thread_list);
+
+       cc->write_thread = kthread_create(dmcrypt_write, cc, "dmcrypt_write");
+       if (IS_ERR(cc->write_thread)) {
+               ret = PTR_ERR(cc->write_thread);
+               cc->write_thread = NULL;
+               ti->error = "Couldn't spawn write thread";
+               goto bad;
+       }
+       wake_up_process(cc->write_thread);
+
        ti->num_flush_bios = 1;
        ti->discard_zeroes_data_unsupported = true;
 
@@ -1798,7 +1872,7 @@ static int crypt_map(struct dm_target *ti, struct bio *bio)
 
        if (bio_data_dir(io->base_bio) == READ) {
                if (kcryptd_io_read(io, GFP_NOWAIT))
-                       kcryptd_queue_io(io);
+                       kcryptd_queue_read(io);
        } else
                kcryptd_queue_crypt(io);