linux-kernel - Re: [PATCH] Documentation: hugetlb: Update hugetlb options

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Message-ID: <868dc6b9-2382-b71d-5aca-495556822f99@redhat.com>
Date:   Fri, 10 Apr 2020 08:02:09 -0400
From:   Nitesh Narayan Lal <nitesh@...hat.com>
To:     Peter Xu <peterx@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] Documentation: hugetlb: Update hugetlb options


On 4/9/20 6:18 PM, Peter Xu wrote:
> On Thu, Apr 09, 2020 at 03:08:07PM -0700, Mike Kravetz wrote:
>> On 4/9/20 2:58 PM, Peter Xu wrote:
>>> The hugepage options are not documented clearly.
>>>
>>> Firstly, default_hugepagesz= should always be specified after the
>>> declaration of the same type of huge page using hugepagesz=.  For
>>> example, if we boot a x86_64 system with kernel cmdline
>>> "default_hugepagesz=2M", we'll get a very funny error message:
>>>
>>> "HugeTLB: unsupported default_hugepagesz 2097152. Reverting to 2097152"
>>>
>>> It's understandable from code-wise because when hugetlb_init() we
>>> didn't have the 2M page hstate registered, so it's unsupported.
>>> However 2M is actually the default huge page size on x86_64, so we'll
>>> register it right after the error message.  However it's very
>>> confusing if without these knowledges.
>>>
>>> Secondly, hugepages= option must be used _after_ another hugepagesz=.
>>> The word "interleave" is fine but it didn't declare the fact that
>>> each of the hugepages= option will be applied to the previous parsed
>>> hugepagesz= option.
>>>
>>> State all these clear.
>>>
>>> Signed-off-by: Peter Xu <peterx@...hat.com>
>> Hi Peter,
>>
>> Did you happen to see this patch series?
>>
>> https://lore.kernel.org/linux-mm/20200401183819.20647-1-mike.kravetz@oracle.com/
>>
>> That should address the documentation issue and more.
> Great!
>
> I missed that, but I'll definitely read it (probably tomorrow).  Let's
> ignore this patch then.

My bad, I didn't realize that Mike has already  pointed you in the right direction.
Please ignore my earlier email. :)

>
> Thanks,
>
-- 
Nitesh



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