linux-kernel - Re: [v3,2/3] powerpc: get hugetlbpage handling more generic

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Message-ID: <aa9a2f8a-a480-0cc9-adf6-4017c771fb46@c-s.fr>
Date:   Fri, 25 Nov 2016 09:14:03 +0100
From:   Christophe LEROY <christophe.leroy@....fr>
To:     Scott Wood <oss@...error.net>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [v3,2/3] powerpc: get hugetlbpage handling more generic



Le 24/11/2016 à 06:23, Scott Wood a écrit :
> On Wed, Sep 21, 2016 at 10:11:54AM +0200, Christophe Leroy wrote:
>> Today there are two implementations of hugetlbpages which are managed
>> by exclusive #ifdefs:
>> * FSL_BOOKE: several directory entries points to the same single hugepage
>> * BOOK3S: one upper level directory entry points to a table of hugepages
>>
>> In preparation of implementation of hugepage support on the 8xx, we
>> need a mix of the two above solutions, because the 8xx needs both cases
>> depending on the size of pages:
>> * In 4k page size mode, each PGD entry covers a 4M bytes area. It means
>> that 2 PGD entries will be necessary to cover an 8M hugepage while a
>> single PGD entry will cover 8x 512k hugepages.
>> * In 16 page size mode, each PGD entry covers a 64M bytes area. It means
>> that 8x 8M hugepages will be covered by one PGD entry and 64x 512k
>> hugepages will be covers by one PGD entry.
>>
>> This patch:
>> * removes #ifdefs in favor of if/else based on the range sizes
>> * merges the two huge_pte_alloc() functions as they are pretty similar
>> * merges the two hugetlbpage_init() functions as they are pretty similar
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
>> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
>
> With this patch on e6500, running the hugetlb testsuite results in the
> system hanging in a storm of OOM killer invocations (I'll try to debug
> more deeply later).  This patch also changes the default hugepage size on
> FSL book3e from 4M to 16M.
>

Regarding the default hugepage size, it is a result of the merge of the 
two hugetlbpage_init().
Should I add an ifdef to get 4M on FSL book3e by default ?
What's the reason for selecting different hugepage sizes depending on 
the CPU ? I thought default size was selected based on what was existing.

What testsuite do you run exactly ?

Christophe