linux-kernel - Re: [v2 3/5] mm: add "zero" argument to vmemmap allocators

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Date:   Wed, 3 May 2017 11:05:45 -0400
From:   Pasha Tatashin <pasha.tatashin@...cle.com>
To:     David Miller <davem@...emloft.net>
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,
        heiko.carstens@...ibm.com, willy@...radead.org
Subject: Re: [v2 3/5] mm: add "zero" argument to vmemmap allocators

Hi Dave,

Thank you for the review. I will address your comment and update patchset..

Pasha

On 05/03/2017 10:34 AM, David Miller wrote:
> From: Pavel Tatashin <pasha.tatashin@...cle.com>
> Date: Fri, 24 Mar 2017 15:19:50 -0400
> 
>> Allow clients to request non-zeroed memory from vmemmap allocator.
>> The following two public function have a new boolean argument called zero:
>>
>> __vmemmap_alloc_block_buf()
>> vmemmap_alloc_block()
>>
>> When zero is true, memory that is allocated by memblock allocator is zeroed
>> (the current behavior), when argument is false, the memory is not zeroed.
>>
>> This change allows for optimizations where client knows when it is better
>> to zero memory: may be later when other CPUs are started, or may be client
>> is going to set every byte in the allocated memory, so no need to zero
>> memory beforehand.
>>
>> Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
>> Reviewed-by: Shannon Nelson <shannon.nelson@...cle.com>
> 
> I think when you add a new argument that can adjust behavior, you
> should add the new argument but retain exactly the current behavior in
> the existing calls.
> 
> Then later you can piece by piece change behavior, and document properly
> in the commit message what is happening and why the transformation is
> legal.
> 
> Here, you are adding the new boolean to __earlyonly_bootmem_alloc() and
> then making sparse_mem_maps_populate_node() pass false, which changes
> behavior such that it doesn't get zero'd memory any more.
> 
> Please make one change at a time.  Otherwise review and bisection is
> going to be difficult.
> 
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