Commit 35b6ddfa authored by Qu Wenruo's avatar Qu Wenruo Committed by David Sterba
Browse files

btrfs: introduce write_one_subpage_eb() function 



The new function, write_one_subpage_eb(), as a subroutine for subpage
metadata write, will handle the extent buffer bio submission.

The major differences between the new write_one_subpage_eb() and
write_one_eb() is:

- No page locking
  When entering write_one_subpage_eb() the page is no longer locked.
  We only lock the page for its status update, and unlock immediately.
  Now we completely rely on extent io tree locking.

- Extra bitmap update along with page status update
  Now page dirty and writeback is controlled by
  btrfs_subpage::dirty_bitmap and btrfs_subpage::writeback_bitmap.
  They both follow the schema that any sector is dirty/writeback, then
  the full page gets dirty/writeback.

- When to update the nr_written number
  Now we take a shortcut, if we have cleared the last dirty bit of the
  page, we update nr_written.
  This is not completely perfect, but should emulate the old behavior
  well enough.

Signed-off-by: default avatarQu Wenruo <wqu@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 2f3186d8

fs/btrfs/extent_io.c

+53 −0
Original line number Diff line number Diff line
@@ -4197,6 +4197,56 @@ static void end_bio_extent_buffer_writepage(struct bio *bio) 
	bio_put(bio);

}



/*

 * Unlike the work in write_one_eb(), we rely completely on extent locking.

 * Page locking is only utilized at minimum to keep the VMM code happy.

 *

 * Caller should still call write_one_eb() other than this function directly.

 * As write_one_eb() has extra preparation before submitting the extent buffer.

 */

static int write_one_subpage_eb(struct extent_buffer *eb,

				struct writeback_control *wbc,

				struct extent_page_data *epd)

{

	struct btrfs_fs_info *fs_info = eb->fs_info;

	struct page *page = eb->pages[0];

	unsigned int write_flags = wbc_to_write_flags(wbc) | REQ_META;

	bool no_dirty_ebs = false;

	int ret;



	/* clear_page_dirty_for_io() in subpage helper needs page locked */

	lock_page(page);

	btrfs_subpage_set_writeback(fs_info, page, eb->start, eb->len);



	/* Check if this is the last dirty bit to update nr_written */

	no_dirty_ebs = btrfs_subpage_clear_and_test_dirty(fs_info, page,

							  eb->start, eb->len);

	if (no_dirty_ebs)

		clear_page_dirty_for_io(page);



	ret = submit_extent_page(REQ_OP_WRITE | write_flags, wbc, page,

			eb->start, eb->len, eb->start - page_offset(page),

			&epd->bio, end_bio_extent_buffer_writepage, 0, 0, 0,

			false);

	if (ret) {

		btrfs_subpage_clear_writeback(fs_info, page, eb->start, eb->len);

		set_btree_ioerr(page, eb);

		unlock_page(page);



		if (atomic_dec_and_test(&eb->io_pages))

			end_extent_buffer_writeback(eb);

		return -EIO;

	}

	unlock_page(page);

	/*

	 * Submission finished without problem, if no range of the page is

	 * dirty anymore, we have submitted a page.  Update nr_written in wbc.

	 */

	if (no_dirty_ebs)

		update_nr_written(wbc, 1);

	return ret;

}



static noinline_for_stack int write_one_eb(struct extent_buffer *eb,

			struct writeback_control *wbc,

			struct extent_page_data *epd)
@@ -4228,6 +4278,9 @@ static noinline_for_stack int write_one_eb(struct extent_buffer *eb, 
		memzero_extent_buffer(eb, start, end - start);

	}



	if (eb->fs_info->sectorsize < PAGE_SIZE)

		return write_one_subpage_eb(eb, wbc, epd);



	for (i = 0; i < num_pages; i++) {

		struct page *p = eb->pages[i];