Re: [PATCH 1/4] block: export part_in_flight()

[Yu Kuai]

Hi,

在 2025/04/14 14:32, Christoph Hellwig 写道:
> On Sat, Apr 12, 2025 at 03:31:59PM +0800, Yu Kuai wrote:
> > From: Yu Kuai <yukuai3@xxxxxxxxxx>
> >
> > This helper will be used in mdraid in later patches, check if there
> > are normal IO inflight while generating background sync IO, to fix a
> > problem in mdraid that foreground IO can be starved by background sync
> > IO.
>
> If we export this it needs a kerneldoc comment, and probably also
> a better name.

Sure about comment.
> Looking at this I'm also a little confused about blk_mq_in_flight_rw vs
> blk_mq_in_flight and why one needs blk-mq special casing and the other
> not, maybe we need to dig into the history and try to understand that
> as well while we're at it.

There are two kinds of helpers:

1) part_in_flight and part_in_flight_rw
2) blk_mq_in_flight and blk_mq_in_flight_rw

1) is accounted at blk_account_io_start(), while 2) is
blk_mq_start_request(), I think this is the essential difference.

part_in_flight_rw() and blk_mq_in_flight_rw() is also used in sysfs API
inflight for bio/rq based device. And commit 7be835694dae ("block: fix
that util can be greater than 100%") convert blk_mq_in_flight() to
part_in_flight() from disk stats API. Now I just checked there is no use
for blk_mq_in_flight() anymore and maybe it can be removed.

Thanks,
Kuai

> .