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

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Message-ID: <20180711124801.GO20050@dhcp22.suse.cz>
Date:   Wed, 11 Jul 2018 14:48:01 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Cannon Matthews <cannonmatthews@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        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 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>

-- 
Michal Hocko
SUSE Labs