Commit 6f3577bd authored by Chris Mason's avatar Chris Mason
Browse files

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: default avatarChris Mason <chris.mason@oracle.com>
parent 5b050f04

fs/btrfs/ctree.c

+4 −4
Original line number Diff line number Diff line
@@ -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)

fs/btrfs/disk-io.c

+3 −3
Original line number Diff line number Diff line
@@ -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)

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