Re: [PATCH 1/3] block: try one write zeroes request before going further

From: Tom Yan <tom.ty89@gmail.com>
To: Hannes Reinecke <hare@suse.de>
Cc: linux-block@vger.kernel.org, linux-scsi@vger.kernel.org,
	Christoph Hellwig <hch@lst.de>,
	tom.leiming@gmail.com, axboe@fb.com
Subject: Re: [PATCH 1/3] block: try one write zeroes request before going further
Date: Sun, 6 Dec 2020 22:07:44 +0800	[thread overview]
Message-ID: <CAGnHSEkTZAvRZc3UyHAsOFdV8r=QpgV=KauqQqYwYHJUF+kAFg@mail.gmail.com> (raw)
In-Reply-To: <ba469342-b94b-4d2d-4af0-085711979a52@suse.de>

Yes it does have "dependency" to the blk_next_bio() patch. I just
somehow missed that.

The problem is, I don't think I'm trying to change the logic of
bio_chain(), or even that of blk_next_bio(). It really just looks like
a careless mistake, that the arguments were typed in the wrong order.

Adding those who signed off the original commit (block: remove struct
bio_batch / 9082e87b) here too to the CC list.

On Sun, 6 Dec 2020 at 21:56, Hannes Reinecke <hare@suse.de> wrote:
>
> On 12/6/20 2:25 PM, Tom Yan wrote:
> > I think you misunderstood it. The goal of this patch is to split the
> > current situation into two chains (or one unchained bio + a series of
> > chained bio). The first one is an attempt/trial which makes sure that
> > the latter large bio chain can actually be handled (as per the
> > "command capability" of the device).
> >
> Oh, I think I do get what you're trying to do. And, in fact, I don't
> argue with what you're trying to achieve.
>
> What I would like to see, though, is keep the current bio_chain logic
> intact (irrespective of your previous patch, which should actually be
> part of this series), and just lift the first check out of the loop:
>
> @@ -262,9 +262,14 @@ static int __blkdev_issue_write_zeroes(struct
> block_device *bdev,
>
>          if (max_write_zeroes_sectors == 0)
>                  return -EOPNOTSUPP;
> -
> +       new = bio_alloc(gfp_mask, 0);
> +       bio_chain(bio, new);
> +       if (submit_bio_wait(bio) == BLK_STS_NOTSUPP) {
> +               bio_put(new);
> +               return -ENOPNOTSUPP;
> +       }
> +       bio = new;
>          while (nr_sects) {
> -               bio = blk_next_bio(bio, 0, gfp_mask);
>                  bio->bi_iter.bi_sector = sector;
>                  bio_set_dev(bio, bdev);
>                  bio->bi_opf = REQ_OP_WRITE_ZEROES;
> @@ -279,6 +284,7 @@ static int __blkdev_issue_write_zeroes(struct
> block_device *bdev,
>                          bio->bi_iter.bi_size = nr_sects << 9;
>                          nr_sects = 0;
>                  }
> +               bio = blk_next_bio(bio, 0, gfp_mask);
>                  cond_resched();
>          }
>
> (The error checking from submit_bio_wait() could be improved :-)
>
> Cheers,
>
> Hannes
> --
> Dr. Hannes Reinecke                Kernel Storage Architect
> hare@suse.de                              +49 911 74053 688
> SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
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