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From:   Jeff Moyer <jmoyer@redhat.com>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Takashi Iwai <tiwai@suse.de>,
        Paolo Valente <paolo.valente@linaro.org>,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [REGRESSION] bfq probe failed on 4.19-rc3
References: <s5ha7ooxbps.wl-tiwai@suse.de>
        <8b5a7dc9-2dc1-16ee-4b05-a72eb6680c77@kernel.dk>
        <x49a7ooj7zp.fsf@segfault.boston.devel.redhat.com>
        <bd71494f-4595-7586-4c46-000f2b2029aa@kernel.dk>
Date:   Tue, 11 Sep 2018 12:51:27 -0400
In-Reply-To: <bd71494f-4595-7586-4c46-000f2b2029aa@kernel.dk> (Jens Axboe's
        message of "Tue, 11 Sep 2018 10:49:05 -0600")
Message-ID: <x495zzcj7u8.fsf@segfault.boston.devel.redhat.com>
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Jens Axboe <axboe@kernel.dk> writes:

> On 9/11/18 10:48 AM, Jeff Moyer wrote:
>> Jens Axboe <axboe@kernel.dk> writes:
>> 
>>> On 9/11/18 10:03 AM, Takashi Iwai wrote:
>>>> Hi,
>>>>
>>>> I noticed that bfq doesn't appear in the I/O scheduler list on
>>>> 4.19-rc3.  It seems that blkcg_policy_register() at the beginning of
>>>> bfq_init() returns -ENOSPC, hence the probe aborts silently.
>>>>
>>>> Is this already addressed?
>>>
>>> Haven't heard about this one before. What kernel did you last use that
>>> worked?
>> 
>> I'm guessing you just need to update the maximum number of policies:
>> 
>> /*
>>  * Maximum number of blkcg policies allowed to be registered concurrently.
>>  * Defined here to simplify include dependency.
>>  */
>> #define BLKCG_MAX_POLS          3
>
> That is my guess too, hence the suggestion to try and disable the
> iolatency policy. Just tried here without, and it works, rebooting
> with to verify that we're running out of policy slots.

Functions calling this function: blkcg_policy_register

  File                      Function       Line
0 block/bfq-iosched.c       bfq_init       5675 ret =
                                                blkcg_policy_register(&blkcg_pol
                                                icy_bfq);
1 block/blk-iolatency.c     iolatency_init  946 return
                                                blkcg_policy_register(&blkcg_pol
                                                icy_iolatency);
2 block/blk-throttle.c      throtl_init    2511 return
                                                blkcg_policy_register(&blkcg_pol
                                                icy_throtl);
3 block/cfq-iosched.c       cfq_init       4869 ret =
                                                blkcg_policy_register(&blkcg_pol
                                                icy_cfq);

And then there were 4...

-Jeff