Re: [PATCH 4/5] blk-lib.c: generic_make_request() handles large bios now

[Christoph Hellwig <hch@infradead.org>]

>  int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
>  		sector_t nr_sects, gfp_t gfp_mask, unsigned long flags)
>  {
> -	DECLARE_COMPLETION_ONSTACK(wait);
>  	struct request_queue *q = bdev_get_queue(bdev);
>  	int type = REQ_WRITE | REQ_DISCARD;
> -	unsigned int max_discard_sectors, granularity;
> -	int alignment;
> -	struct bio_batch bb;
>  	struct bio *bio;
>  	int ret = 0;
> -	struct blk_plug plug;
>  
>  	if (!q)
>  		return -ENXIO;
> @@ -56,78 +34,28 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
>  	if (!blk_queue_discard(q))
>  		return -EOPNOTSUPP;
>  
> -	/* Zero-sector (unknown) and one-sector granularities are the same.  */
> -	granularity = max(q->limits.discard_granularity >> 9, 1U);
> -	alignment = (bdev_discard_alignment(bdev) >> 9) % granularity;
> -
> -	/*
> -	 * Ensure that max_discard_sectors is of the proper
> -	 * granularity, so that requests stay aligned after a split.
> -	 */
> -	max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9);
> -	max_discard_sectors -= max_discard_sectors % granularity;

Seems like this is also missing the code to trim down the request to
be properly aligned to the device limit.  I don't think our low-level
drivers are ready to handle this, and even if they were it should be a
separate change.