linux-kernel - Re: "mm: use early_pfn_to_nid in page_ext

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Message-ID: <20170704105342.GJ14722@dhcp22.suse.cz>
Date:   Tue, 4 Jul 2017 12:53:42 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Joonsoo Kim <js1304@...il.com>, Yang Shi <yang.shi@...aro.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: "mm: use early_pfn_to_nid in page_ext_init" broken on some
 configurations?

On Tue 04-07-17 11:39:57, Vlastimil Babka wrote:
> On 07/04/2017 07:23 AM, Joonsoo Kim wrote:
> > On Mon, Jul 03, 2017 at 04:18:01PM +0200, Vlastimil Babka wrote:
> >> allocated" looks much more sane there. But there's a warning nevertheless.
> > 
> > Warning would comes from the fact that drain_all_pages() is called
> > before mm_percpu_wq is initialised. We could remove WARN_ON_ONCE() and add
> > drain_local_page(zone) to fix the problem.
> 
> Wouldn't that still leave some period during boot where kernel already
> runs on multiple CPU's, but mm_percpu_wq is not yet initialized and
> somebody tries to use it? We want to catch such cases, right?

I haven't checked the boot sequence but if we know that we need
mm_percpu_wq initialized earlier than moving it should be not a big deal
I guess.
-- 
Michal Hocko
SUSE Labs