linux-kernel - Re: [v2 5/5] mm: teach platforms not to zero struct pages memory

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Date:   Fri, 07 Apr 2017 11:45:23 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:     Heiko Carstens <heiko.carstens@...ibm.com>,
        Pavel Tatashin <pasha.tatashin@...cle.com>
Cc:     linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, borntraeger@...ibm.com,
        davem@...emloft.net, willy@...radead.org
Subject: Re: [v2 5/5] mm: teach platforms not to zero struct pages memory

Heiko Carstens <heiko.carstens@...ibm.com> writes:

> On Fri, Mar 24, 2017 at 03:19:52PM -0400, Pavel Tatashin wrote:
>> If we are using deferred struct page initialization feature, most of
>> "struct page"es are getting initialized after other CPUs are started, and
>> hence we are benefiting from doing this job in parallel. However, we are
>> still zeroing all the memory that is allocated for "struct pages" using the
>> boot CPU.  This patch solves this problem, by deferring zeroing "struct
>> pages" to only when they are initialized.
>> 
>> Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
>> Reviewed-by: Shannon Nelson <shannon.nelson@...cle.com>
>> ---
>>  arch/powerpc/mm/init_64.c |    2 +-
>>  arch/s390/mm/vmem.c       |    2 +-
>>  arch/sparc/mm/init_64.c   |    2 +-
>>  arch/x86/mm/init_64.c     |    2 +-
>>  4 files changed, 4 insertions(+), 4 deletions(-)
>> 
>> diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
>> index eb4c270..24faf2d 100644
>> --- a/arch/powerpc/mm/init_64.c
>> +++ b/arch/powerpc/mm/init_64.c
>> @@ -181,7 +181,7 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node)
>>  		if (vmemmap_populated(start, page_size))
>>  			continue;
>> 
>> -		p = vmemmap_alloc_block(page_size, node, true);
>> +		p = vmemmap_alloc_block(page_size, node, VMEMMAP_ZERO);
>>  		if (!p)
>>  			return -ENOMEM;
>> 
>> diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c
>> index 9c75214..ffe9ba1 100644
>> --- a/arch/s390/mm/vmem.c
>> +++ b/arch/s390/mm/vmem.c
>> @@ -252,7 +252,7 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node)
>>  				void *new_page;
>> 
>>  				new_page = vmemmap_alloc_block(PMD_SIZE, node,
>> -							       true);
>> +							       VMEMMAP_ZERO);
>>  				if (!new_page)
>>  					goto out;
>>  				pmd_val(*pm_dir) = __pa(new_page) | sgt_prot;
>
> s390 has two call sites that need to be converted, like you did in one of
> your previous patches. The same seems to be true for powerpc, unless there
> is a reason to not convert them?
>

vmemmap_list_alloc is not really struct page allocation right ? We are
just allocating memory to be used as vmemmmap_backing. But considering
we are updating all the three elements of the sturct, we can avoid that
memset . But instead of VMEMMAP_ZERO we can just pass false in that case
?

-aneesh