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

[Hannes Reinecke <hare@suse.de>]

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
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