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

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Message-ID: <b6617b4b-bcab-3b40-7d46-46a5d9682856@gpiccoli.net>
Date:   Tue, 15 Oct 2019 10:58:36 -0300
From:   "Guilherme G. Piccoli" <guilherme@...ccoli.net>
To:     Michal Hocko <mhocko@...nel.org>,
        Guilherme Piccoli <gpiccoli@...onical.com>
Cc:     Qian Cai <cai@....pw>, linux-mm@...ck.org, mike.kravetz@...cle.com,
        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 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.

As I've said before, Ubuntu kdump rely on rootfs mounting and there's no 
official statement or documentation that say it's wrong to do this way - 
although I agree initrd-only approach is more safe. But since Ubuntu 
kdump rely on rootfs mount, we couldn't find a way to effectively 
prevent the creation of hugepages completely, hence we tried to 
introduce one.

Cheers,

Guilherme