linux-kernel - Re: [PATCH] powerpc/mm: Implemented default

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Message-Id: <231a6e252020968b7eff8dd25dbb126b@linux.vnet.ibm.com>
Date:   Wed, 12 Jul 2017 12:15:10 -0300
From:   victora <victora@...ux.vnet.ibm.com>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:     Victor Aoqui <victora@...ibm.com>, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, mpe@...erman.id.au
Subject: Re: [PATCH] powerpc/mm: Implemented default_hugepagesz verification
 for powerpc

Em 2017-07-05 13:03, victora escreveu:
> Em 2017-07-05 01:26, Aneesh Kumar K.V escreveu:
>> On Tuesday 04 July 2017 01:35 AM, Victor Aoqui wrote:
>>> Implemented default hugepage size verification (default_hugepagesz=)
>>> in order to allow allocation of defined number of pages (hugepages=)
>>> only for supported hugepage sizes.
>>> 
>>> Signed-off-by: Victor Aoqui <victora@...ibm.com>
>>> ---
>>>   arch/powerpc/mm/hugetlbpage.c | 15 +++++++++++++++
>>>   1 file changed, 15 insertions(+)
>>> 
>>> diff --git a/arch/powerpc/mm/hugetlbpage.c 
>>> b/arch/powerpc/mm/hugetlbpage.c
>>> index a4f33de..464e72e 100644
>>> --- a/arch/powerpc/mm/hugetlbpage.c
>>> +++ b/arch/powerpc/mm/hugetlbpage.c
>>> @@ -797,6 +797,21 @@ static int __init hugepage_setup_sz(char *str)
>>>   }
>>>   __setup("hugepagesz=", hugepage_setup_sz);
>>> 
>>> +static int __init default_hugepage_setup_sz(char *str)
>>> +{
>>> +        unsigned long long size;
>>> +
>>> +        size = memparse(str, &str);
>>> +
>>> +        if (add_huge_page_size(size) != 0) {
>>> +                hugetlb_bad_size();
>>> +                pr_err("Invalid default huge page size 
>>> specified(%llu)\n", size);
>>> +        }
>>> +
>>> +        return 1;
>>> +}
>>> +__setup("default_hugepagesz=", default_hugepage_setup_sz);
>> 
>> isn't that a behavior change in what we have now ? . Right now if size
>> specified is not supported, we fallback to HPAGE_SIZE.
> 
> Yes, it is. However, is this a correct behavior? If we specify an
> unsupported value, for example default_hugepagesz=1M and
> hugepages=1000, 1M will be ignored and 1000 pages of 16M (arch
> default) will be allocated. This could lead to non-expected out of of
> memory/performance issue.
> 
>> 
>> mm/hugetlb.c
>> 
>> if (!size_to_hstate(default_hstate_size)) {
>> 	default_hstate_size = HPAGE_SIZE;
>> 	if (!size_to_hstate(default_hstate_size))
>> 		hugetlb_add_hstate(HUGETLB_PAGE_ORDER);
>> }
>> 
>> 
>>> +
>>>   struct kmem_cache *hugepte_cache;
>>>   static int __init hugetlbpage_init(void)
>>>   {
>>> 
>> 
>> Even if we want to do this, this should be done in generic code and
>> should not be powerpc specific
>> 
> 
> The verification of supported powerpc hugepage size (hugepagesz=) is
> being performed on add_huge_page_size(), which is currently defined in
> arch/powerpc/mm/hugetlbpage.c. I think it makes more sense to
> implement default_hugepagesz= verification on arch/powerpc, don't you
> think?
> 
>> -aneesh

Hi Aneesh,

Did you have time to review the comments above?

Thanks
Victor