btrfs: hooks for readahead

This adds the hooks needed for readahead. In the readpage_end_io_hook,
the extent state is checked for the EXTENT_READAHEAD flag. Only in this
case the readahead hook is called, to keep the impact on non-ra as low
as possible.
Additionally, a hook for a failed IO is added, otherwise readahead would
wait indefinitely for the extent to finish.

Changes for v2:
 - eliminate race condition

Signed-off-by: Arne Jansen <sensille@gmx.net>

1 files changed, 37 insertions, 0 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index fd28c40e9ec3..2151828aa142 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -609,11 +609,47 @@ static int btree_readpage_end_io_hook(struct page *page, u64 start, u64 end,
         end = min_t(u64, eb->len, PAGE_CACHE_SIZE);
         end = eb->start + end - 1;
 err:
+        if (test_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags)) {
+                clear_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags);
+                btree_readahead_hook(root, eb, eb->start, ret);
+        }
+
         free_extent_buffer(eb);
 out:
         return ret;
 }
 
+static int btree_io_failed_hook(struct bio *failed_bio,
+                         struct page *page, u64 start, u64 end,
+                         struct extent_state *state)
+{
+        struct extent_io_tree *tree;
+        unsigned long len;
+        struct extent_buffer *eb;
+        struct btrfs_root *root = BTRFS_I(page->mapping->host)->root;
+
+        tree = &BTRFS_I(page->mapping->host)->io_tree;
+        if (page->private == EXTENT_PAGE_PRIVATE)
+                goto out;
+        if (!page->private)
+                goto out;
+
+        len = page->private >> 2;
+        WARN_ON(len == 0);
+
+        eb = alloc_extent_buffer(tree, start, len, page);
+        if (eb == NULL)
+                goto out;
+
+        if (test_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags)) {
+                clear_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags);
+                btree_readahead_hook(root, eb, eb->start, -EIO);
+        }
+
+out:
+        return -EIO;    /* we fixed nothing */
+}
+
 static void end_workqueue_bio(struct bio *bio, int err)
 {
         struct end_io_wq *end_io_wq = bio->bi_private;
@@ -3166,6 +3202,7 @@ static int btrfs_cleanup_transaction(struct btrfs_root *root)
 static struct extent_io_ops btree_extent_io_ops = {
         .write_cache_pages_lock_hook = btree_lock_page_hook,
         .readpage_end_io_hook = btree_readpage_end_io_hook,
+        .readpage_io_failed_hook = btree_io_failed_hook,
         .submit_bio_hook = btree_submit_bio_hook,
         /* note we're sharing with inode.c for the merge bio hook */
         .merge_bio_hook = btrfs_merge_bio_hook,