btrfs: introduce read_extent_buffer_subpage()
Introduce a helper, read_extent_buffer_subpage(), to do the subpage
extent buffer read.
The difference between regular and subpage routines are:
- No page locking
Here we completely rely on extent locking.
Page locking can reduce the concurrency greatly, as if we lock one
page to read one extent buffer, all the other extent buffers in the
same page will have to wait.
- Extent uptodate condition
Despite the existing PageUptodate() and EXTENT_BUFFER_UPTODATE check,
We also need to check btrfs_subpage::uptodate_bitmap.
- No page iteration
Just one page, no need to loop, this greatly simplified the subpage
routine.
This patch only implements the bio submit part, no endio support yet.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
1 file changed
