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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Fri, 18 Jun 2021 16:41:58 +0200
Message-ID: <CAJfpegu0prjjHVhBzwZBVk5N+avHvUcyi4ovhKbf+F7GEuVkmw@mail.gmail.com>
Subject: Re: [PATCH] backing_dev_info: introduce min_bw/max_bw limits
To:     Michael Stapelberg <stapelberg+linux@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-mm <linux-mm@kvack.org>,
        linux-fsdevel@vger.kernel.org, Tejun Heo <tj@kernel.org>,
        Dennis Zhou <dennis@kernel.org>, Jens Axboe <axboe@kernel.dk>,
        Roman Gushchin <guro@fb.com>,
        Johannes Thumshirn <johannes.thumshirn@wdc.com>,
        Jan Kara <jack@suse.cz>, Song Liu <song@kernel.org>,
        David Sterba <dsterba@suse.com>
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On Fri, 18 Jun 2021 at 10:31, Michael Stapelberg
<stapelberg+linux@google.com> wrote:

> Maybe, but I don=E2=80=99t have the expertise, motivation or time to
> investigate this any further, let alone commit to get it done.
> During our previous discussion I got the impression that nobody else
> had any cycles for this either:
> https://lore.kernel.org/linux-fsdevel/CANnVG6n=3DySfe1gOr=3D0ituQidp56idG=
ARDKHzP0hv=3DERedeMrMA@mail.gmail.com/
>
> Have you had a look at the China LSF report at
> http://bardofschool.blogspot.com/2011/?
> The author of the heuristic has spent significant effort and time
> coming up with what we currently have in the kernel:
>
> """
> Fengguang said he draw more than 10K performance graphs and read even
> more in the past year.
> """
>
> This implies that making changes to the heuristic will not be a quick fix=
.

Having a piece of kernel code sitting there that nobody is willing to
fix is certainly not a great situation to be in.

And introducing band aids is not going improve the above situation,
more likely it will prolong it even further.

Thanks,
Miklos