linux-kernel - Re: [RFC PATCH] mm/oom: detect and kill task which has allocation forbidden by cpuset limit

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Message-ID: <YS+ItADNn08hCLPY@dhcp22.suse.cz>
Date:   Wed, 1 Sep 2021 16:05:40 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Feng Tang <feng.tang@...el.com>
Cc:     David Rientjes <rientjes@...gle.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian Brauner <christian@...uner.io>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] mm/oom: detect and kill task which has allocation
 forbidden by cpuset limit

On Wed 01-09-21 21:42:00, Feng Tang wrote:
[...]
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index eeb3a9cb36bb..d1ae77be45a2 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4271,10 +4271,18 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
>  		.gfp_mask = gfp_mask,
>  		.order = order,
>  	};
> -	struct page *page;
> +	struct page *page = NULL;
> +	struct zoneref *z;
>  
>  	*did_some_progress = 0;
>  
> +	if (cpusets_enabled() && (gfp_mask & __GFP_HARDWALL)) {
> +		z = first_zones_zonelist(ac->zonelist,
> +			gfp_zone(gfp_mask), &cpuset_current_mems_allowed);
> +		if (!z->zone)
> +			goto out;
> +	}
> +

This looks better than the previous attempt. It would be still better to
solve this at the page allocator layer. The slowpath is already doing
this for the nodemask. E.g.

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index eeb3a9cb36bb..a3193134540d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4929,6 +4929,17 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 	if (!ac->preferred_zoneref->zone)
 		goto nopage;
 
+	/*
+	 * Check for insane configurations where the cpuset doesn't contain any suitable
+	 * zone to satisfy the request - e.g. kernel allocations from MOVABLE nodes only
+	 */
+	if (cpusets_enabled() && (gfp_mask & __GFP_HARDWALL)) {
+		struct zoneref *z = first_zones_zonelist(ac->zonelist, ac->highest_zoneidx,
+				&cpuset_current_mems_allowed);
+		if (!z->zone)
+			goto nopage;
+	}
+
 	if (alloc_flags & ALLOC_KSWAPD)
 		wake_all_kswapds(order, gfp_mask, ac);
 
if this is seen as an additional overhead for an insane configuration
then we can add insane_cpusets_enabled() which would be a static branch
enabled when somebody actually tries to configure movable only cpusets
or potentially other dubious usage.
-- 
Michal Hocko
SUSE Labs