Btrfs: Wait for async bio submissions to make some progress at queue time

Before, the btrfs bdi congestion function was used to test for too many
async bios.  This keeps that check to throttle pdflush, but also
adds a check while queuing bios.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 17 insertions, 1 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 23a5b0aba00a..2652660e6079 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -138,12 +138,18 @@ int run_scheduled_bios(struct btrfs_device *device)
 {
         struct bio *pending;
         struct backing_dev_info *bdi;
+        struct btrfs_fs_info *fs_info;
         struct bio *tail;
         struct bio *cur;
         int again = 0;
         unsigned long num_run = 0;
+        unsigned long limit;
 
         bdi = device->bdev->bd_inode->i_mapping->backing_dev_info;
+        fs_info = device->dev_root->fs_info;
+        limit = btrfs_async_submit_limit(fs_info);
+        limit = limit * 2 / 3;
+
 loop:
         spin_lock(&device->io_lock);
 
@@ -179,7 +185,11 @@ loop:
                 cur = pending;
                 pending = pending->bi_next;
                 cur->bi_next = NULL;
-                atomic_dec(&device->dev_root->fs_info->nr_async_bios);
+                atomic_dec(&fs_info->nr_async_bios);
+
+                if (atomic_read(&fs_info->nr_async_bios) < limit &&
+                    waitqueue_active(&fs_info->async_submit_wait))
+                        wake_up(&fs_info->async_submit_wait);
 
                 BUG_ON(atomic_read(&cur->bi_cnt) == 0);
                 bio_get(cur);
@@ -2135,6 +2145,7 @@ int schedule_bio(struct btrfs_root *root, struct btrfs_device *device,
                  int rw, struct bio *bio)
 {
         int should_queue = 1;
+        unsigned long limit;
 
         /* don't bother with additional async steps for reads, right now */
         if (!(rw & (1 << BIO_RW))) {
@@ -2171,6 +2182,11 @@ int schedule_bio(struct btrfs_root *root, struct btrfs_device *device,
         if (should_queue)
                 btrfs_queue_worker(&root->fs_info->submit_workers,
                                    &device->work);
+
+        limit = btrfs_async_submit_limit(root->fs_info);
+        wait_event_timeout(root->fs_info->async_submit_wait,
+                           (atomic_read(&root->fs_info->nr_async_bios) < limit),
+                           HZ/10);
         return 0;
 }