linux-kernel - Re: [PATCH v2 2/3] powerpc: get hugetlbpage handling more generic

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Message-Id: <874m5bxpai.fsf@linux.vnet.ibm.com>
Date:   Tue, 20 Sep 2016 08:15:09 +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 v2 2/3] powerpc: get hugetlbpage handling more generic

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

>>
>>
>>>  	for (psize = 0; psize < MMU_PAGE_COUNT; ++psize) {
>>>  		unsigned shift;
>>>  		unsigned pdshift;
>>> @@ -860,16 +807,31 @@ static int __init hugetlbpage_init(void)
>>>  		 * if we have pdshift and shift value same, we don't
>>>  		 * use pgt cache for hugepd.
>>>  		 */
>>> -		if (pdshift != shift) {
>>> +		if (pdshift > shift) {
>>>  			pgtable_cache_add(pdshift - shift, NULL);
>>>  			if (!PGT_CACHE(pdshift - shift))
>>>  				panic("hugetlbpage_init(): could not create "
>>>  				      "pgtable cache for %d bit pagesize\n", shift);
>>> +		} else if (!hugepte_cache) {
>>> +			/*
>>> +			 * Create a kmem cache for hugeptes.  The bottom bits in
>>> +			 * the pte have size information encoded in them, so
>>> +			 * align them to allow this
>>> +			 */
>>> +			hugepte_cache = kmem_cache_create("hugepte-cache",
>>> +							  sizeof(pte_t),
>>> +							  HUGEPD_SHIFT_MASK + 1,
>>> +							  0, NULL);
>>> +			if (hugepte_cache == NULL)
>>> +				panic("%s: Unable to create kmem cache "
>>> +				      "for hugeptes\n", __func__);
>>> +
>>
>>
>> We don't need hugepte_cache for book3s 64K. I guess we will endup
>> creating one here ?
>
> Should not, because on book3s 64k, we will have pdshift > shift
> won't we ?
>

on 64k book3s, we have pdshift == shift and we don't need to create 
hugepd cache on book3s 64k.

-aneesh