linux-kernel - Re: [PATCH] hugetlb: Add nohugepages parameter to prevent hugepages creation

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Message-ID: <2df9c30d-b1e0-648e-93ba-85c78fbcbd0e@oracle.com>
Date:   Fri, 18 Oct 2019 11:29:40 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     "Guilherme G. Piccoli" <guilherme@...ccoli.net>,
        Michal Hocko <mhocko@...nel.org>, Qian Cai <cai@....pw>
Cc:     Guilherme Piccoli <gpiccoli@...onical.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Jay Vosburgh <jay.vosburgh@...onical.com>,
        "Guilherme G. Piccoli" <kernel@...ccoli.net>
Subject: Re: [PATCH] hugetlb: Add nohugepages parameter to prevent hugepages
 creation

On 10/15/19 7:09 AM, Guilherme G. Piccoli wrote:
> 
> 
> On 10/15/19 11:05 AM, Michal Hocko wrote:
>> On Tue 15-10-19 10:58:36, Guilherme G. Piccoli wrote:
>>> On 10/15/19 9:18 AM, Michal Hocko wrote:
>>>> I do agree with Qian Cai here. Kdump kernel requires a very tailored
>>>> environment considering it is running in a very restricted
>>>> configuration. The hugetlb pre-allocation sounds like a tooling problem
>>>> and should be fixed at that layer.
>>>>
>>>
>>> Hi Michal, thanks for your response. Can you suggest me a current way of
>>> preventing hugepages for being created, using userspace? The goal for this
>>> patch is exactly this, introduce such a way.
>>
>> Simply restrict the environment to not allocate any hugepages? Kdump
>> already controls the kernel command line and it also starts only a very
>> minimal subset of services. So who is allocating those hugepages?
>> sysctls should be already excluded by default as Qian mentioned.
>>
> 
> 
> OK, thanks Michal and Qian, I'll try to make things work from kdump perspective. The trick part is exactly preventing the sysctl to get applied heh
> 

Please do let us know if this can be done in tooling.

I am not opposed to the approach taken in your v2 patch as it essentially
uses the hugepages_supported() functionality that exists today.  However,
it seems that other distros have ways around this issue.  As such, I would
prefer if the issue was addressed in the tooling.
-- 
Mike Kravetz