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Date:   Sun, 8 Oct 2023 13:36:03 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     Yu Kuai <yukuai1@huaweicloud.com>
Cc:     Li Nan <linan666@huaweicloud.com>,
        Khazhy Kumykov <khazhy@chromium.org>, tj@kernel.org,
        josef@toxicpanda.com, axboe@kernel.dk, cgroups@vger.kernel.org,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        yi.zhang@huawei.com, houtao1@huawei.com, yangerkun@huawei.com,
        "yukuai (C)" <yukuai3@huawei.com>
Subject: Re: [PATCH] blk-throttle: Calculate allowed value only when the
 throttle is enabled
Message-ID: <20231008113602.GB24726@redhat.com>
References: <20230928015858.1809934-1-linan666@huaweicloud.com>
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 <4ace01e8-6815-29d0-70ce-4632818ca701@huaweicloud.com>
 <20231005162417.GA32420@redhat.com>
 <0a8f34aa-ced9-e613-3e5f-b5e53a3ef3d9@huaweicloud.com>
 <20231007151607.GA24726@redhat.com>
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On 10/08, Yu Kuai wrote:
>
> >>  static u64 calculate_bytes_allowed(u64 bps_limit, unsigned long
> >>jiffy_elapsed)
> >>  {
> >>+       if (jiffy_elapsed > HZ &&
> >>+           bps_limit > mul_u64_u64_div_u64(U64_MAX, (u64)HZ,
> >>(u64)jiffy_elapsed);
> >>+               return U64_MAX;
> >>+
> >
> >I can't suggest anything better...
> >
> >but I do not know if it is possible that HZ > jiffy_elapsed. If yes, then
> >mul_u64_u64_div_u64() above is not safe too.
>
> Well, 'jiffy_elapsed > HZ' is judged before mul_u64_u64_div_u64().

Yes, sorry, somehow I didn't notice this check.

Oleg.