linux-kernel - Re: [PATCH v5 00/21] Free some vmemmap pages of hugetlb page

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Date:   Mon, 23 Nov 2020 22:01:13 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Michal Hocko <mhocko@...e.com>,
        David Hildenbrand <david@...hat.com>,
        Muchun Song <songmuchun@...edance.com>, corbet@....net,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        hpa@...or.com, dave.hansen@...ux.intel.com, luto@...nel.org,
        peterz@...radead.org, viro@...iv.linux.org.uk,
        akpm@...ux-foundation.org, paulmck@...nel.org,
        mchehab+huawei@...nel.org, pawan.kumar.gupta@...ux.intel.com,
        rdunlap@...radead.org, oneukum@...e.com, anshuman.khandual@....com,
        jroedel@...e.de, almasrymina@...gle.com, rientjes@...gle.com,
        osalvador@...e.de, song.bao.hua@...ilicon.com,
        duanxiongchun@...edance.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v5 00/21] Free some vmemmap pages of hugetlb page

On Mon, Nov 23, 2020 at 01:52:13PM -0800, Mike Kravetz wrote:
> On 11/22/20 11:38 PM, Michal Hocko wrote:
> > On Fri 20-11-20 09:45:12, Mike Kravetz wrote:
> >> Not sure if I agree with that last statement.  Database and virtualization
> >> use cases from my employer allocate allocate hugetlb pages after boot.  It
> >> is shortly after boot, but still not from boot/kernel command line.
> > 
> > Is there any strong reason for that?
> 
> The reason I have been given is that it is preferable to have SW compute
> the number of needed huge pages after boot based on total memory, rather
> than have a sysadmin calculate the number and add a boot parameter.

Oh, I remember this bug!  I think it was posted publically, even.
If the sysadmin configures, say, 90% of the RAM to be hugepages and
then a DIMM fails and the sysadmin doesn't remember to adjust the boot
parameter, Linux does some pretty horrible things and the symptom is
"Linux doesn't boot".