[PATCH 3.16 226/366] mm: hugetlb: yield when prepping struct pages

[Ben Hutchings]

3.16.61-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Cannon Matthews <cannonmatthews@xxxxxxxxxx>

commit 520495fe96d74e05db585fc748351e0504d8f40d upstream.

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.

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.

Link: http://lkml.kernel.org/r/20180627214447.260804-1-cannonmatthews@xxxxxxxxxx
Signed-off-by: Cannon Matthews <cannonmatthews@xxxxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Andres Lagar-Cavilla <andreslc@xxxxxxxxxx>
Cc: Peter Feiner <pfeiner@xxxxxxxxxx>
Cc: Greg Thelen <gthelen@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 mm/hugetlb.c | 1 +
 1 file changed, 1 insertion(+)

--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1546,6 +1546,7 @@ static void __init gather_bootmem_preall
 		 */
 		if (hstate_is_gigantic(h))
 			adjust_managed_page_count(page, 1 << h->order);
+		cond_resched();
 	}
 }