linux-kernel - Re: [PATCH] mm: hugetlb: don't zero 1GiB bootmem pages.

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Date:   Wed, 11 Jul 2018 09:47:25 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Michal Hocko <mhocko@...nel.org>,
        Cannon Matthews <cannonmatthews@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Nadia Yvette Chambers <nyc@...omorphy.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        andreslc@...gle.com, pfeiner@...gle.com, dmatlack@...gle.com,
        gthelen@...gle.com
Subject: Re: [PATCH] mm: hugetlb: don't zero 1GiB bootmem pages.

On 07/11/2018 05:48 AM, Michal Hocko wrote:
> On Wed 11-07-18 14:47:11, Michal Hocko wrote:
>> On Tue 10-07-18 11:49:03, Cannon Matthews wrote:
>>> When using 1GiB pages during early boot, use the new
>>> memblock_virt_alloc_try_nid_raw() function to allocate memory without
>>> zeroing it.  Zeroing out hundreds or thousands of GiB in a single core
>>> memset() call is very slow, and can make early boot last upwards of
>>> 20-30 minutes on multi TiB machines.
>>>
>>> To be safe, still zero the first sizeof(struct boomem_huge_page) bytes
>>> since this is used a temporary storage place for this info until
>>> gather_bootmem_prealloc() processes them later.
>>>
>>> The rest of the memory does not need to be zero'd as the hugetlb pages
>>> are always zero'd on page fault.
>>>
>>> Tested: Booted with ~3800 1G pages, and it booted successfully in
>>> roughly the same amount of time as with 0, as opposed to the 25+
>>> minutes it would take before.
>>
>> The patch makes perfect sense to me. I wasn't even aware that it
>> zeroying memblock allocation. Thanks for spotting this and fixing it.
>>
>>> Signed-off-by: Cannon Matthews <cannonmatthews@...gle.com>
>>
>> I just do not think we need to to zero huge_bootmem_page portion of it.
>> It should be sufficient to INIT_LIST_HEAD before list_add. We do
>> initialize the rest explicitly already.
> 
> Forgot to mention that after that is addressed you can add
> Acked-by: Michal Hocko <mhocko@...e.com>

Cannon,

How about if you make this change suggested by Michal, and I will submit
a separate patch to revert the patch which added the phys field to
huge_bootmem_page structure.

FWIW,
Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>

-- 
Mike Kravetz