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Date:   Fri, 07 Nov 2014 10:30:28 -0800
From:   David Daney <ddaney.cavm@gmail.com>
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To:     Joshua Kinard <kumba@gentoo.org>
CC:     Ralf Baechle <ralf@linux-mips.org>,
        Linux MIPS List <linux-mips@linux-mips.org>
Subject: Re: IP27: CONFIG_TRANSPARENT_HUGEPAGE triggers bus errors
References: <54560D3B.8060602@gentoo.org> <5457CF0A.7020303@gmail.com> <5458272A.7050309@gentoo.org> <54582A91.8040401@gmail.com> <20141105160945.GB13785@linux-mips.org> <545C9D4D.4090501@gentoo.org>
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On 11/07/2014 02:22 AM, Joshua Kinard wrote:
[...]
>
> So my guess is unless hugepages can happen in powers of 4,

Huge  pages are currently only supported on MIPS64 for this reason.

huge_page_mask_size = (normal_page_size/8 * normal_page_size) / 2;

If you take log2 of everything you get

huge_page_mask_bits = normal_page_bits - 3 + normal_page_bits - 1
   = 2 * normal_page_bits - 4 (always even)

So all page sizes result in huge pages that meet the power of 4 criterion.

> they're not
> compatible w/ the R10K-series (and likely not the R5K/RM7K, either, since they
> all have the same 24:13 bits in the PageMask register).  It seems the logical
> choice would be to remove 'select CPU_SUPPORTS_HUGEPAGES' from CPU_R5000,
> CPU_NEVADA, CPU_R10000, and CPU_RM7000 in arch/mips/Kconfig.
>