Commit 6bc5636a authored by Qu Wenruo's avatar Qu Wenruo Committed by David Sterba
Browse files

btrfs: refactor __extent_writepage_io() to improve readability 



The refactoring involves the following modifications:

- iosize alignment
  In fact we don't really need to manually do alignment at all.
  All extent maps should already be aligned, thus basic ASSERT() check
  would be enough.

- redundant variables
  We have extra variable like blocksize/pg_offset/end.
  They are all unnecessary.

  @blocksize can be replaced by sectorsize size directly, and it's only
  used to verify the em start/size is aligned.

  @pg_offset can be easily calculated using @cur and page_offset(page).

  @end is just assigned from @page_end and never modified, use
  "start + PAGE_SIZE - 1" directly and remove @page_end.

- remove some BUG_ON()s
  The BUG_ON()s are for extent map, which we have tree-checker to check
  on-disk extent data item and runtime check.
  ASSERT() should be enough.

Reviewed-by: default avatarJosef Bacik <josef@toxicpanda.com>
Signed-off-by: default avatarQu Wenruo <wqu@suse.com>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 0c64c33c

fs/btrfs/extent_io.c

+16 −21
Original line number Diff line number Diff line
@@ -3513,23 +3513,20 @@ static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode, 
				 unsigned long nr_written,

				 int *nr_ret)

{

	struct btrfs_fs_info *fs_info = inode->root->fs_info;

	struct extent_io_tree *tree = &inode->io_tree;

	u64 start = page_offset(page);

	u64 page_end = start + PAGE_SIZE - 1;

	u64 end;

	u64 end = start + PAGE_SIZE - 1;

	u64 cur = start;

	u64 extent_offset;

	u64 block_start;

	u64 iosize;

	struct extent_map *em;

	size_t pg_offset = 0;

	size_t blocksize;

	int ret = 0;

	int nr = 0;

	const unsigned int write_flags = wbc_to_write_flags(wbc);

	bool compressed;



	ret = btrfs_writepage_cow_fixup(page, start, page_end);

	ret = btrfs_writepage_cow_fixup(page, start, end);

	if (ret) {

		/* Fixup worker will requeue */

		redirty_page_for_writepage(wbc, page);
@@ -3544,16 +3541,13 @@ static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode, 
	 */

	update_nr_written(wbc, nr_written + 1);



	end = page_end;

	blocksize = inode->vfs_inode.i_sb->s_blocksize;



	while (cur <= end) {

		u64 disk_bytenr;

		u64 em_end;

		u32 iosize;



		if (cur >= i_size) {

			btrfs_writepage_endio_finish_ordered(page, cur,

							     page_end, 1);

			btrfs_writepage_endio_finish_ordered(page, cur, end, 1);

			break;

		}

		em = btrfs_get_extent(inode, NULL, 0, cur, end - cur + 1);
@@ -3565,13 +3559,16 @@ static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode, 


		extent_offset = cur - em->start;

		em_end = extent_map_end(em);

		BUG_ON(em_end <= cur);

		BUG_ON(end < cur);

		iosize = min(em_end - cur, end - cur + 1);

		iosize = ALIGN(iosize, blocksize);

		disk_bytenr = em->block_start + extent_offset;

		ASSERT(cur <= em_end);

		ASSERT(cur < end);

		ASSERT(IS_ALIGNED(em->start, fs_info->sectorsize));

		ASSERT(IS_ALIGNED(em->len, fs_info->sectorsize));

		block_start = em->block_start;

		compressed = test_bit(EXTENT_FLAG_COMPRESSED, &em->flags);

		disk_bytenr = em->block_start + extent_offset;



		/* Note that em_end from extent_map_end() is exclusive */

		iosize = min(em_end, end + 1) - cur;

		free_extent_map(em);

		em = NULL;
@@ -3587,7 +3584,6 @@ static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode, 
				btrfs_writepage_endio_finish_ordered(page, cur,

							cur + iosize - 1, 1);

			cur += iosize;

			pg_offset += iosize;

			continue;

		}
@@ -3599,8 +3595,8 @@ static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode, 
		}



		ret = submit_extent_page(REQ_OP_WRITE | write_flags, wbc,

					 page, disk_bytenr, iosize, pg_offset,

					 &epd->bio,

					 page, disk_bytenr, iosize,

					 cur - page_offset(page), &epd->bio,

					 end_bio_extent_writepage,

					 0, 0, 0, false);

		if (ret) {
@@ -3609,8 +3605,7 @@ static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode, 
				end_page_writeback(page);

		}



		cur = cur + iosize;

		pg_offset += iosize;

		cur += iosize;

		nr++;

	}

	*nr_ret = nr;