Re: [PATCH 1/4] Btrfs: map the node block when looking for readahead targets
From: Arne Jansen <hidden>
Date: 2011-06-08 08:21:57
On 11.05.2011 23:35, Josef Bacik wrote:
quoted hunk ↗ jump to hunk
If we have particularly full nodes, we could call btrfs_node_blockptr up to 32 times, which is 32 pairs of kmap/kunmap, which _sucks_. So go ahead and map the extent buffer while we look for readahead targets. Thanks, Signed-off-by: Josef Bacik <redacted> --- fs/btrfs/ctree.c | 23 +++++++++++++++++++++-- 1 files changed, 21 insertions(+), 2 deletions(-)diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c index 84d7ca1..009bcf7 100644 --- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c@@ -1229,6 +1229,7 @@ static void reada_for_search(struct btrfs_root *root, u64 search; u64 target; u64 nread = 0; + u64 gen; int direction = path->reada; struct extent_buffer *eb; u32 nr;@@ -1256,6 +1257,15 @@ static void reada_for_search(struct btrfs_root *root, nritems = btrfs_header_nritems(node); nr = slot; while (1) { + if (!node->map_token) { + unsigned long offset = btrfs_node_key_ptr_offset(nr); + map_private_extent_buffer(node, offset, + sizeof(struct btrfs_key_ptr), + &node->map_token, + &node->kaddr, + &node->map_start, + &node->map_len, KM_USER1);
You can't do that. It puts us in atomic context, and the following readahead_tree_block will try a memory allocation with GFP_NOFS, which leads to a BUG: sleeping function called from invalid context. It didn't fall on our feet earlier because you also turned off readahead, but scrub still uses it. -Arne
quoted hunk ↗ jump to hunk
+ } if (direction < 0) { if (nr == 0) break;@@ -1273,14 +1283,23 @@ static void reada_for_search(struct btrfs_root *root, search = btrfs_node_blockptr(node, nr); if ((search <= target && target - search <= 65536) || (search > target && search - target <= 65536)) { - readahead_tree_block(root, search, blocksize, - btrfs_node_ptr_generation(node, nr)); + gen = btrfs_node_ptr_generation(node, nr); + if (node->map_token) { + unmap_extent_buffer(node, node->map_token, + KM_USER1); + node->map_token = NULL; + } + readahead_tree_block(root, search, blocksize, gen); nread += blocksize; } nscan++; if ((nread > 65536 || nscan > 32)) break; } + if (node->map_token) { + unmap_extent_buffer(node, node->map_token, KM_USER1); + node->map_token = NULL; + } } /*