linux-kernel - Re: [PATCH] vmscan: force scan offline memory cgroups

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150108170349.GA32079@phnom.home.cmpxchg.org>
Date:	Thu, 8 Jan 2015 12:03:49 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>, Tejun Heo <tj@...nel.org>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vmscan: force scan offline memory cgroups

On Thu, Jan 08, 2015 at 05:51:09PM +0300, Vladimir Davydov wrote:
> Since commit b2052564e66d ("mm: memcontrol: continue cache reclaim from
> offlined groups") pages charged to a memory cgroup are not reparented
> when the cgroup is removed. Instead, they are supposed to be reclaimed
> in a regular way, along with pages accounted to online memory cgroups.
> 
> However, an lruvec of an offline memory cgroup will sooner or later get
> so small that it will be scanned only at low scan priorities (see
> get_scan_count()). Therefore, if there are enough reclaimable pages in
> big lruvecs, pages accounted to offline memory cgroups will never be
> scanned at all, wasting memory.
> 
> Fix this by unconditionally forcing scanning dead lruvecs from kswapd.
> 
> Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>

Yes, it makes sense to continue draining them at this point.  I just
have a few comments inline:

> @@ -1367,6 +1367,20 @@ int mem_cgroup_inactive_anon_is_low(struct lruvec *lruvec)
>  	return inactive * inactive_ratio < active;
>  }
>  
> +bool mem_cgroup_need_force_scan(struct lruvec *lruvec)
> +{
> +	struct mem_cgroup_per_zone *mz;
> +	struct mem_cgroup *memcg;
> +
> +	if (mem_cgroup_disabled())
> +		return false;
> +
> +	mz = container_of(lruvec, struct mem_cgroup_per_zone, lruvec);
> +	memcg = mz->memcg;
> +
> +	return !(memcg->css.flags & CSS_ONLINE);
> +}

It's better to name functions after what they do, rather than what
they are used for, to make reuse easy.  mem_cgroup_lruvec_online()?

> @@ -1935,7 +1935,8 @@ static void get_scan_count(struct lruvec *lruvec, int swappiness,
>  	 * latencies, so it's better to scan a minimum amount there as
>  	 * well.
>  	 */
> -	if (current_is_kswapd() && !zone_reclaimable(zone))
> +	if (current_is_kswapd() &&
> +	    (!zone_reclaimable(zone) || mem_cgroup_need_force_scan(lruvec)))
>  		force_scan = true;

This would probably be easier on the eyes if you broke that up:

if (current_is_kswapd()) {
        if (!zone_reclaimable(zone))
                force_scan = true;
        else if (!mem_cgroup_online_from_lruvec(lruvec))
                force_scan = true;
} else if (!global_reclaim(sc)) {
                force_scan = true;
}
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/