linux-kernel - Re: [PATCH] mm: hugetlb: yield when prepping struct pages

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Date:   Thu, 28 Jun 2018 13:21:39 +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, gthelen@...gle.com
Subject: Re: [PATCH] mm: hugetlb: yield when prepping struct pages

On Wed 27-06-18 14:44:47, Cannon Matthews wrote:
> When booting with very large numbers of gigantic (i.e. 1G) pages, the
> operations in the loop of gather_bootmem_prealloc, and specifically
> prep_compound_gigantic_page, takes a very long time, and can cause a
> softlockup if enough pages are requested at boot.
> 
> For example booting with 3844 1G pages requires prepping
> (set_compound_head, init the count) over 1 billion 4K tail pages, which
> takes considerable time. This should also apply to reserving the same
> amount of memory as 2M pages, as the same number of struct pages
> are affected in either case.
> 
> Add a cond_resched() to the outer loop in gather_bootmem_prealloc() to
> prevent this lockup.
> 
> Tested: Booted with softlockup_panic=1 hugepagesz=1G hugepages=3844 and
> no softlockup is reported, and the hugepages are reported as
> successfully setup.
> 
> Signed-off-by: Cannon Matthews <cannonmatthews@...gle.com>

Acked-by: Michal Hocko <mhocko@...e.com>

Thanks!

> ---
>  mm/hugetlb.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index a963f2034dfc..d38273c32d3b 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2169,6 +2169,7 @@ static void __init gather_bootmem_prealloc(void)
>  		 */
>  		if (hstate_is_gigantic(h))
>  			adjust_managed_page_count(page, 1 << h->order);
> +		cond_resched();
>  	}
>  }
>  
> -- 
> 2.18.0.rc2.346.g013aa6912e-goog

-- 
Michal Hocko
SUSE Labs