linux-kernel - Re: [PATCH 3/4] mm, page_alloc: Drain per-cpu pages from workqueue context

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 for Android: free password hash cracker in your pocket

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

Message-ID: <20170120152606.w3hb53m2w6thzsqq@techsingularity.net>
Date:   Fri, 20 Jan 2017 15:26:06 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Hillf Danton <hillf.zj@...baba-inc.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Petr Mladek <pmladek@...e.cz>
Subject: Re: [PATCH 3/4] mm, page_alloc: Drain per-cpu pages from workqueue
 context

On Fri, Jan 20, 2017 at 03:26:05PM +0100, Vlastimil Babka wrote:
> > @@ -2392,8 +2404,24 @@ void drain_all_pages(struct zone *zone)
> >  		else
> >  			cpumask_clear_cpu(cpu, &cpus_with_pcps);
> >  	}
> > -	on_each_cpu_mask(&cpus_with_pcps, (smp_call_func_t) drain_local_pages,
> > -								zone, 1);
> > +
> > +	if (works) {
> > +		for_each_cpu(cpu, &cpus_with_pcps) {
> > +			struct work_struct *work = per_cpu_ptr(works, cpu);
> > +			INIT_WORK(work, drain_local_pages_wq);
> > +			schedule_work_on(cpu, work);
> 
> This translates to queue_work_on(), which has the comment of "We queue
> the work to a specific CPU, the caller must ensure it can't go away.",
> so is this safe? lru_add_drain_all() uses get_online_cpus() around this.
> 

get_online_cpus() would be required.

> schedule_work_on() also uses the generic system_wq, while lru drain has
> its own workqueue with WQ_MEM_RECLAIM so it seems that would be useful
> here as well?
> 

I would be reluctant to introduce a dedicated queue unless there was a
definite case where an OOM occurred because pages were pinned on per-cpu
lists and couldn't be drained because the buddy allocator was depleted.
As it was, I thought the fallback case was excessively paranoid.

> > +		}
> > +		for_each_cpu(cpu, &cpus_with_pcps)
> > +			flush_work(per_cpu_ptr(works, cpu));
> > +	} else {
> > +		for_each_cpu(cpu, &cpus_with_pcps) {
> > +			struct work_struct work;
> > +
> > +			INIT_WORK(&work, drain_local_pages_wq);
> > +			schedule_work_on(cpu, &work);
> > +			flush_work(&work);
> 
> Totally out of scope, but I wonder if schedule_on_each_cpu() could use
> the same fallback that's here?
> 

I'm not aware of a case where it really has been a problem. I only considered
it here as the likely caller is in a context that is failing allocations.

-- 
Mel Gorman
SUSE Labs