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

From: Christoph Hellwig
Date: Wed Nov 27 2013 - 07:54:17 EST


> 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.

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