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Date:   Mon, 30 Nov 2020 17:05:48 +0000
From:   Christoph Hellwig <hch@infradead.org>
To:     Jeffle Xu <jefflexu@linux.alibaba.com>
Cc:     axboe@kernel.dk, linux-block@vger.kernel.org,
        joseph.qi@linux.alibaba.com
Subject: Re: [PATCH] block: fix inflight statistics of part0
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On Thu, Nov 26, 2020 at 05:48:33PM +0800, Jeffle Xu wrote:
> The inflight of partition 0 doesn't include inflight IOs to all
> sub-partitions, since currently mq calculates inflight of specific
> partition by simply camparing the value of the partition pointer.
> 
> Thus the following case is possible:
> 
> $ cat /sys/block/vda/inflight
> ?? ?? ?? ??0 ?? ?? ?? ??0
> $ cat /sys/block/vda/vda1/inflight
> ?? ?? ?? ??0 ?? ?? ??128
> 
> Partition 0 should be specially handled since it represents the whole
> disk.

I'm not sure and can see arguments for either side.  In doubt we should
stick to historic behavior, can you check what old kernels (especially
before blk-mq) did?