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

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Message-ID: <20170123230429.os7ssxab4mazrkrb@techsingularity.net>
Date:   Mon, 23 Jan 2017 23:04:29 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Tejun Heo <tj@...nel.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        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 Mon, Jan 23, 2017 at 03:55:01PM -0500, Tejun Heo wrote:
> Hello, Mel.
> 
> On Mon, Jan 23, 2017 at 08:04:12PM +0000, Mel Gorman wrote:
> > What is the actual mechanism that does that? It's not something that
> > schedule_on_each_cpu does and one would expect that the core workqueue
> > implementation would get this sort of detail correct. Or is this a proposal
> > on how it should be done?
> 
> If you use schedule_on_each_cpu(), it's all fine as the thing pins
> cpus and waits for all the work items synchronously.  If you wanna do
> it asynchronously, right now, you'll have to manually synchronize work
> items against the offline callback manually.
> 

Is the current implementation and what it does wrong in some way? I ask
because synchronising against the offline callback sounds like it would
be a bit of a maintenance mess for relatively little gain.

-- 
Mel Gorman
SUSE Labs