Re: [PATCH] btrfs: don't merge pages into bio if their page offset is not continuous

[Christoph Hellwig <hch@lst.de>]

> +	if (bio_ctrl->compress_type != BTRFS_COMPRESS_NONE) {
>  		contig = bio->bi_iter.bi_sector == sector;
> -	else
> -		contig = bio_end_sector(bio) == sector;
> +	} else {

I don't tink we can lose the bio_end_sector check here.

Also if you touch this, invrting the check so that it is

	if (bio_ctrl->compress_type == BTRFS_COMPRESS_NONE) {
		/* main version here */
	} else {
		/* compressed special case */
	}

might make it a bit readable.

> +		struct bio_vec *bvec;
> +
> +		/* Empty bio, we can always add page into it. */
> +		if (bio->bi_iter.bi_size == 0) {

This is also true for the compressed case, isn't it?

So maybe:

	if (bio->bi_iter.bi_size == 0) {
		contig = true;
	} else if (bio_ctrl->compress_type == BTRFS_COMPRESS_NONE) {
		struct bio_vec *bvec = bio_last_bvec_all(bio);

		/*
		 * The contig check requires the following conditions to be met:
		 * 1) The pages are belonging to the same inode
		 * 2) The range has adjacent logical bytenr
		 * 3) The range has adjacent file offset (NEW)
		 *    This is required for the usage of btrfs_bio->file_offset.
		 */
		contig = bio_end_sector(bio) == sector &&
			    page_offset(bvec->bv_page) + bvec->bv_offset +
			    bvec->bv_len == page_offset(page) + pg_offset);
	} else {
		contig = bio->bi_iter.bi_sector == sector;
	}

(we don't need the mapping check, as all the submit_extent_page
always loops over the same mapping)