linux-kernel - Re: [PATCH v4 15/20] powerpc/mm: Avoid useless lock with single page fragments

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Date:   Tue, 25 Sep 2018 18:49:07 +0200
From:   Christophe LEROY <christophe.leroy@....fr>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        aneesh.kumar@...ux.vnet.ibm.com
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v4 15/20] powerpc/mm: Avoid useless lock with single page
 fragments



Le 19/09/2018 à 04:56, Aneesh Kumar K.V a écrit :
> On 9/18/18 10:27 PM, Christophe Leroy wrote:
>> There is no point in taking the page table lock as
>> pte_frag is always NULL when we have only one fragment.
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
>> ---
>>   arch/powerpc/mm/pgtable-frag.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/powerpc/mm/pgtable-frag.c 
>> b/arch/powerpc/mm/pgtable-frag.c
>> index bc924822dcd6..ab4910e92aaf 100644
>> --- a/arch/powerpc/mm/pgtable-frag.c
>> +++ b/arch/powerpc/mm/pgtable-frag.c
>> @@ -85,6 +85,9 @@ static pte_t *get_pte_from_cache(struct mm_struct *mm)
>>   {
>>       void *pte_frag, *ret;
>>
>> +    if (PTE_FRAG_NR == 1)
>> +        return NULL;
>> +
>>       spin_lock(&mm->page_table_lock);
>>       ret = mm->context.pte_frag;
>>       if (ret) {
>>
> 
> May be update get_pmd_from_cache too?
> 

Ok, done in v5

Christophe