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

From: Michal Hocko
Date: Thu Jun 28 2018 - 15:03:50 EST


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@xxxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

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