Btrfs: Improve metadata read latencies

This fixes latency problems on metadata reads by making sure they
don't go through the async submit queue, and by tuning down the amount
of readahead done during btree searches.

Also, the btrfs bdi congestion function is tuned to ignore the
number of pending async bios and checksums pending.  There is additional
code that throttles new async bios now and the congestion function
doesn't need to worry about it anymore.

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

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index f82f8db02275912ec50dba3e18a31e698bed183a..ac61c50a331156d73d864a78067636b45817d500 100644 (file)
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1285,16 +1285,16 @@ static noinline void reada_for_search(struct btrfs_root *root,
                }
                search = btrfs_node_blockptr(node, nr);
                if ((search >= lowest_read && search <= highest_read) ||
-                   (search < lowest_read && lowest_read - search <= 32768) ||
-                   (search > highest_read && search - highest_read <= 32768)) {
+                   (search < lowest_read && lowest_read - search <= 16384) ||
+                   (search > highest_read && search - highest_read <= 16384)) {
                        readahead_tree_block(root, search, blocksize,
                                     btrfs_node_ptr_generation(node, nr));
                        nread += blocksize;
                }
                nscan++;
-               if (path->reada < 2 && (nread > (256 * 1024) || nscan > 32))
+               if (path->reada < 2 && (nread > (64 * 1024) || nscan > 32))
                        break;
-               if(nread > (1024 * 1024) || nscan > 128)
+               if(nread > (256 * 1024) || nscan > 128)
                        break;
 
                if (search < lowest_read)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 1bb54d69fbb24416f80a2fd17151274c64042577..3b0e974a9e9c5aec034139852f7cc458ac67a0db 100644 (file)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -605,7 +605,7 @@ static int btree_submit_bio_hook(struct inode *inode, int rw, struct bio *bio,
                BUG_ON(ret);
 
                return btrfs_map_bio(BTRFS_I(inode)->root, rw, bio,
-                                    mirror_num, 1);
+                                    mirror_num, 0);
        }
        return btrfs_wq_submit_bio(BTRFS_I(inode)->root->fs_info,
                                   inode, rw, bio, mirror_num, 0,
@@ -1139,11 +1139,11 @@ static int btrfs_congested_fn(void *congested_data, int bdi_bits)
        struct list_head *cur;
        struct btrfs_device *device;
        struct backing_dev_info *bdi;
-
+#if 0
        if ((bdi_bits & (1 << BDI_write_congested)) &&
            btrfs_congested_async(info, 0))
                return 1;
-
+#endif
        list_for_each(cur, &info->fs_devices->devices) {
                device = list_entry(cur, struct btrfs_device, dev_list);
                if (!device->bdev)