Btrfs: Fix streaming read performance with checksumming on
Large streaming reads make for large bios, which means each entry on the
list async work queues represents a large amount of data. IO
congestion throttling on the device was kicking in before the async
worker threads decided a single thread was busy and needed some help.
The end result was that a streaming read would result in a single CPU
running at 100% instead of balancing the work off to other CPUs.
This patch also changes the pre-IO checksum lookup done by reads to
work on a per-bio basis instead of a per-page. This results in many
extra btree lookups on large streaming reads. Doing the checksum lookup
right before bio submit allows us to reuse searches while processing
adjacent offsets.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index c4afa9d..31d52c5 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -374,6 +374,10 @@
BUG_ON(ret);
if (!(rw & (1 << BIO_RW))) {
+ if (!btrfs_test_opt(root, NODATASUM) &&
+ !btrfs_test_flag(inode, NODATASUM)) {
+ btrfs_lookup_bio_sums(root, inode, bio);
+ }
goto mapit;
}
@@ -598,58 +602,6 @@
return btrfs_finish_ordered_io(page->mapping->host, start, end);
}
-int btrfs_readpage_io_hook(struct page *page, u64 start, u64 end)
-{
- int ret = 0;
- struct inode *inode = page->mapping->host;
- struct btrfs_root *root = BTRFS_I(inode)->root;
- struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
- struct btrfs_csum_item *item;
- struct btrfs_path *path = NULL;
- u32 csum;
-
- if (btrfs_test_opt(root, NODATASUM) ||
- btrfs_test_flag(inode, NODATASUM))
- return 0;
-
- /*
- * It is possible there is an ordered extent that has
- * not yet finished for this range in the file. If so,
- * that extent will have a csum cached, and it will insert
- * the sum after all the blocks in the extent are fully
- * on disk. So, look for an ordered extent and use the
- * sum if found. We have to do this before looking in the
- * btree because csum items are pre-inserted based on
- * the file size. btrfs_lookup_csum might find an item
- * that still hasn't been fully filled.
- */
- ret = btrfs_find_ordered_sum(inode, start, &csum);
- if (ret == 0)
- goto found;
-
- ret = 0;
- path = btrfs_alloc_path();
- item = btrfs_lookup_csum(NULL, root, path, inode->i_ino, start, 0);
- if (IS_ERR(item)) {
- ret = PTR_ERR(item);
- /* a csum that isn't present is a preallocated region. */
- if (ret == -ENOENT || ret == -EFBIG)
- ret = 0;
- csum = 0;
- printk("no csum found for inode %lu start %Lu\n", inode->i_ino,
- start);
- goto out;
- }
- read_extent_buffer(path->nodes[0], &csum, (unsigned long)item,
- BTRFS_CRC32_SIZE);
-found:
- set_state_private(io_tree, start, csum);
-out:
- if (path)
- btrfs_free_path(path);
- return ret;
-}
-
struct io_failure_record {
struct page *page;
u64 start;
@@ -3613,7 +3565,6 @@
.fill_delalloc = run_delalloc_range,
.submit_bio_hook = btrfs_submit_bio_hook,
.merge_bio_hook = btrfs_merge_bio_hook,
- .readpage_io_hook = btrfs_readpage_io_hook,
.readpage_end_io_hook = btrfs_readpage_end_io_hook,
.writepage_end_io_hook = btrfs_writepage_end_io_hook,
.writepage_start_hook = btrfs_writepage_start_hook,