linux-kernel - Re: [PATCH v2 1/2] mm: call touch_nmi_watchdog() on max order boundaries in deferred init

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Message-ID: <20200402074615.GI22681@dhcp22.suse.cz>
Date:   Thu, 2 Apr 2020 09:46:15 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        linux-mm@...ck.org, dan.j.williams@...el.com,
        shile.zhang@...ux.alibaba.com, daniel.m.jordan@...cle.com,
        ktkhai@...tuozzo.com, david@...hat.com, jmorris@...ei.org,
        sashal@...nel.org, vbabka@...e.cz
Subject: Re: [PATCH v2 1/2] mm: call touch_nmi_watchdog() on max order
 boundaries in deferred init

I have only now noticed that you have reposted.

On Wed 01-04-20 18:57:22, Pavel Tatashin wrote:
> From: Daniel Jordan <daniel.m.jordan@...cle.com>
> 
> 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.
> 
> Fixes: 3a2d7fa8a3d5 ("mm: disable interrupts while initializing deferred pages")
> Cc: stable@...r.kernel.org # 4.17+

This patch is not fixing anything, right? It cleans up the code to make
further changes easier which is good.

> Signed-off-by: Daniel Jordan <daniel.m.jordan@...cle.com>
> Signed-off-by: Pavel Tatashin <pasha.tatashin@...een.com>

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

> ---
>  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 3c4eb750a199..e8ff6a176164 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++;
>  		}
> @@ -1809,8 +1807,10 @@ 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);
>  
> @@ -1894,6 +1894,7 @@ deferred_grow_zone(struct zone *zone, unsigned int order)
>  		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)
> -- 
> 2.17.1
> 

-- 
Michal Hocko
SUSE Labs