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

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Message-ID: <ba5c87df-9a77-ebd2-e45e-f262a36fbf22@oracle.com>
Date:   Thu, 9 Apr 2020 15:08:07 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Peter Xu <peterx@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     Nitesh Narayan Lal <nitesh@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] Documentation: hugetlb: Update hugetlb options

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.
-- 
Mike Kravetz