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

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Message-ID: <20200409221819.GA3172@xz-x1>
Date:   Thu, 9 Apr 2020 18:18:19 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Nitesh Narayan Lal <nitesh@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] Documentation: hugetlb: Update hugetlb options

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.

Thanks,

-- 
Peter Xu