On Wed 01-04-20 16:08:55, Daniel Jordan wrote:
[...]
> From: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
> Date: Fri, 27 Mar 2020 17:29:05 -0400
> Subject: [PATCH] mm: call touch_nmi_watchdog() on max order boundaries in
> deferred init
>
> deferred_init_memmap() disables interrupts the entire time, so it calls
> touch_nmi_watchdog() periodically to avoid soft lockup splats. Soon it
> will run with interrupts enabled, at which point cond_resched() should
> be used instead.
>
> deferred_grow_zone() makes the same watchdog calls through code shared
> with deferred init but will continue to run with interrupts disabled, so
> it can't call cond_resched().
>
> Pull the watchdog calls up to these two places to allow the first to be
> changed later, independently of the second. The frequency reduces from
> twice per pageblock (init and free) to once per max order block.
This makes sense but I am not really sure this is necessary for the
stable backport.
> Signed-off-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> mm/page_alloc.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 212734c4f8b0..4cf18c534233 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1639,7 +1639,6 @@ static void __init deferred_free_pages(unsigned long pfn,
> } else if (!(pfn & nr_pgmask)) {
> deferred_free_range(pfn - nr_free, nr_free);
> nr_free = 1;
> - touch_nmi_watchdog();
> } else {
> nr_free++;
> }
> @@ -1669,7 +1668,6 @@ static unsigned long __init deferred_init_pages(struct zone *zone,
> continue;
> } else if (!page || !(pfn & nr_pgmask)) {
> page = pfn_to_page(pfn);
> - touch_nmi_watchdog();
> } else {
> page++;
> }
> @@ -1813,8 +1811,10 @@ static int __init deferred_init_memmap(void *data)
> * that we can avoid introducing any issues with the buddy
> * allocator.
> */
> - while (spfn < epfn)
> + while (spfn < epfn) {
> nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn);
> + touch_nmi_watchdog();
> + }
> zone_empty:
> pgdat_resize_unlock(pgdat, &flags);
>
> @@ -1908,6 +1908,7 @@ deferred_grow_zone_locked(pg_data_t *pgdat, struct zone *zone,
> first_deferred_pfn = spfn;
>
> nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn);
> + touch_nmi_watchdog();
>
> /* We should only stop along section boundaries */
> if ((first_deferred_pfn ^ spfn) < PAGES_PER_SECTION)
> --
> 2.25.0
>
--
Michal Hocko
SUSE Labs
