Btrfs: Wait for kernel threads to make progress during async submission

Before this change, btrfs would use a bdi congestion function to make
sure there weren't too many pending async checksum work items.

This change makes the process creating async work items wait instead,
leading to fewer congestion returns from the bdi.  This improves
pdflush background_writeout scanning.

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

1 files changed, 26 insertions, 19 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 1bf210dadef6..1aed1f4616b6 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -429,31 +429,36 @@ int btrfs_bio_wq_end_io(struct btrfs_fs_info *info, struct bio *bio,
         return 0;
 }
 
-int btrfs_congested_async(struct btrfs_fs_info *info, int iodone)
+static unsigned long async_submit_limit(struct btrfs_fs_info *info)
 {
-        int limit = 256 * info->fs_devices->open_devices;
-
-        if (iodone)
-                limit = (limit * 3) / 2;
-        if (atomic_read(&info->nr_async_submits) > limit)
-                return 1;
+        unsigned long limit = min_t(unsigned long,
+                                    info->workers.max_workers,
+                                    info->fs_devices->open_devices);
+        return 256 * limit;
+}
 
-        return atomic_read(&info->nr_async_bios) > limit;
+int btrfs_congested_async(struct btrfs_fs_info *info, int iodone)
+{
+        return atomic_read(&info->nr_async_bios) > async_submit_limit(info);
 }
 
 static void run_one_async_submit(struct btrfs_work *work)
 {
         struct btrfs_fs_info *fs_info;
         struct async_submit_bio *async;
+        int limit;
 
         async = container_of(work, struct  async_submit_bio, work);
         fs_info = BTRFS_I(async->inode)->root->fs_info;
+
+        limit = async_submit_limit(fs_info);
+        limit = limit * 2 / 3;
+
         atomic_dec(&fs_info->nr_async_submits);
 
-        if ((async->bio->bi_rw & (1 << BIO_RW)) &&
-            !btrfs_congested_async(fs_info, 1)) {
-                clear_bdi_congested(&fs_info->bdi, WRITE);
-        }
+        if (atomic_read(&fs_info->nr_async_submits) < limit)
+                wake_up(&fs_info->async_submit_wait);
+
         async->submit_bio_hook(async->inode, async->rw, async->bio,
                                async->mirror_num);
         kfree(async);
@@ -464,6 +469,7 @@ int btrfs_wq_submit_bio(struct btrfs_fs_info *fs_info, struct inode *inode,
                         extent_submit_bio_hook_t *submit_bio_hook)
 {
         struct async_submit_bio *async;
+        int limit = async_submit_limit(fs_info);
 
         async = kmalloc(sizeof(*async), GFP_NOFS);
         if (!async)
@@ -478,6 +484,10 @@ int btrfs_wq_submit_bio(struct btrfs_fs_info *fs_info, struct inode *inode,
         async->work.flags = 0;
         atomic_inc(&fs_info->nr_async_submits);
         btrfs_queue_worker(&fs_info->workers, &async->work);
+
+        wait_event_timeout(fs_info->async_submit_wait,
+                           (atomic_read(&fs_info->nr_async_submits) < limit),
+                           HZ/10);
         return 0;
 }
 
@@ -545,16 +555,11 @@ static int btree_writepages(struct address_space *mapping,
         if (wbc->sync_mode == WB_SYNC_NONE) {
                 u64 num_dirty;
                 u64 start = 0;
-                unsigned long thresh = 96 * 1024 * 1024;
+                unsigned long thresh = 8 * 1024 * 1024;
 
                 if (wbc->for_kupdate)
                         return 0;
 
-                if (current_is_pdflush()) {
-                        thresh = 96 * 1024 * 1024;
-                } else {
-                        thresh = 8 * 1024 * 1024;
-                }
                 num_dirty = count_range_bits(tree, &start, (u64)-1,
                                              thresh, EXTENT_DIRTY);
                 if (num_dirty < thresh) {
@@ -1333,6 +1338,7 @@ struct btrfs_root *open_ctree(struct super_block *sb,
         mutex_init(&fs_info->volume_mutex);
         init_waitqueue_head(&fs_info->transaction_throttle);
         init_waitqueue_head(&fs_info->transaction_wait);
+        init_waitqueue_head(&fs_info->async_submit_wait);
 
 #if 0
         ret = add_hasher(fs_info, "crc32c");
@@ -1380,6 +1386,7 @@ struct btrfs_root *open_ctree(struct super_block *sb,
          * devices
          */
         fs_info->submit_workers.idle_thresh = 64;
+        fs_info->workers.idle_thresh = 32;
 
         btrfs_init_workers(&fs_info->fixup_workers, "fixup", 1);
         btrfs_init_workers(&fs_info->endio_workers, "endio",
@@ -1849,7 +1856,7 @@ void btrfs_btree_balance_dirty(struct btrfs_root *root, unsigned long nr)
         struct extent_io_tree *tree;
         u64 num_dirty;
         u64 start = 0;
-        unsigned long thresh = 2 * 1024 * 1024;
+        unsigned long thresh = 12 * 1024 * 1024;
         tree = &BTRFS_I(root->fs_info->btree_inode)->io_tree;
 
         if (current_is_pdflush())