linux-kernel - Re: [PATCH v3 3/3] powerpc/8xx: Implement support of hugepages

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Message-Id: <8760ppw5od.fsf@linux.vnet.ibm.com>
Date:   Wed, 21 Sep 2016 22:28:42 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Scott Wood <oss@...error.net>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v3 3/3] powerpc/8xx: Implement support of hugepages

Christophe Leroy <christophe.leroy@....fr> writes:

> 8xx uses a two level page table with two different linux page size
> support (4k and 16k). 8xx also support two different hugepage sizes
> 512k and 8M. In order to support them on linux we define two different
> page table layout.
>
> The size of pages is in the PGD entry, using PS field (bits 28-29):
> 00 : Small pages (4k or 16k)
> 01 : 512k pages
> 10 : reserved
> 11 : 8M pages
>
> For 512K hugepage size a pgd entry have the below format
> [<hugepte address >0101] . The hugepte table allocated will contain 8
> entries pointing to 512K huge pte in 4k pages mode and 64 entries in
> 16k pages mode.
>
> For 8M in 16k mode, a pgd entry have the below format
> [<hugepte address >1101] . The hugepte table allocated will contain 8
> entries pointing to 8M huge pte.
>
> For 8M in 4k mode, multiple pgd entries point to the same hugepte
> address and pgd entry will have the below format
> [<hugepte address>1101]. The hugepte table allocated will only have one
> entry.
>
> For the time being, we do not support CPU15 ERRATA when HUGETLB is
> selected
>

For the generic bits
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>

> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> ---
> v2: This v1 was split in two parts. This part focuses on adding the
> support on 8xx. It also fixes an error in TLBmiss handlers in the
> case of 8M hugepages in 16k pages mode.
>

-aneesh