From a717531942f488209dded30f6bc648167bcefa72 Mon Sep 17 00:00:00 2001 From: Chris Mason Date: Thu, 22 Jan 2009 09:23:10 -0500 Subject: [PATCH] Btrfs: do less aggressive btree readahead Just before reading a leaf, btrfs scans the node for blocks that are close by and reads them too. It tries to build up a large window of IO looking for blocks that are within a max distance from the top and bottom of the IO window. This patch changes things to just look for blocks within 64k of the target block. It will trigger less IO and make for lower latencies on the read size. Signed-off-by: Chris Mason --- fs/btrfs/ctree.c | 21 +++++---------------- 1 file changed, 5 insertions(+), 16 deletions(-) diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c index 9e46c0776816..2603ee539b7a 100644 --- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -1210,8 +1210,7 @@ static noinline void reada_for_search(struct btrfs_root *root, struct btrfs_disk_key disk_key; u32 nritems; u64 search; - u64 lowest_read; - u64 highest_read; + u64 target; u64 nread = 0; int direction = path->reada; struct extent_buffer *eb; @@ -1235,8 +1234,7 @@ static noinline void reada_for_search(struct btrfs_root *root, return; } - highest_read = search; - lowest_read = search; + target = search; nritems = btrfs_header_nritems(node); nr = slot; @@ -1256,24 +1254,15 @@ static noinline void reada_for_search(struct btrfs_root *root, break; } search = btrfs_node_blockptr(node, nr); - if ((search >= lowest_read && search <= highest_read) || - (search < lowest_read && lowest_read - search <= 16384) || - (search > highest_read && search - highest_read <= 16384)) { + if ((search <= target && target - search <= 65536) || + (search > target && search - target <= 65536)) { readahead_tree_block(root, search, blocksize, btrfs_node_ptr_generation(node, nr)); nread += blocksize; } nscan++; - if (path->reada < 2 && (nread > (64 * 1024) || nscan > 32)) + if ((nread > 65536 || nscan > 32)) break; - - if (nread > (256 * 1024) || nscan > 128) - break; - - if (search < lowest_read) - lowest_read = search; - if (search > highest_read) - highest_read = search; } } -- 2.20.1