dm snapshot: persistent make metadata_wq multithreaded

metadata_wq serves on-stack work items from chunk_io().  Even if
multiple chunk_io() are simultaneously in progress, each is
independent and queued only once, so multithreaded workqueue can be
safely used.

Switch metadata_wq to multithread and flush the work item instead of
the workqueue in chunk_io().

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

diff --git a/drivers/md/dm-snap-persistent.c b/drivers/md/dm-snap-persistent.c
index d3021a69c85735d50b78364a79ee3c6e0270b123..95891dfcbca021563a465751dacf064aee3a46df 100644 (file)
--- a/drivers/md/dm-snap-persistent.c
+++ b/drivers/md/dm-snap-persistent.c
@@ -256,7 +256,7 @@ static int chunk_io(struct pstore *ps, void *area, chunk_t chunk, int rw,
         */
        INIT_WORK_ONSTACK(&req.work, do_metadata);
        queue_work(ps->metadata_wq, &req.work);
-       flush_workqueue(ps->metadata_wq);
+       flush_work(&req.work);
 
        return req.result;
 }
@@ -818,7 +818,7 @@ static int persistent_ctr(struct dm_exception_store *store,
        atomic_set(&ps->pending_count, 0);
        ps->callbacks = NULL;
 
-       ps->metadata_wq = alloc_ordered_workqueue("ksnaphd", WQ_MEM_RECLAIM);
+       ps->metadata_wq = alloc_workqueue("ksnaphd", WQ_MEM_RECLAIM, 0);
        if (!ps->metadata_wq) {
                kfree(ps);
                DMERR("couldn't start header metadata update thread");