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Date:   Tue, 5 Jan 2021 08:28:51 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Matthew Wilcox <willy@infradead.org>, Hui Su <sh_def@163.com>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/page_alloc: remove the static for local variable
 node_order
Message-ID: <20210105072851.GO13207@dhcp22.suse.cz>
References: <20201230114014.GA1934427@ubuntu-A520I-AC>
 <20201230124233.GE28221@casper.infradead.org>
 <20210104152357.d56d10e0443bae984a174f18@linux-foundation.org>
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On Mon 04-01-21 15:23:57, Andrew Morton wrote:
> On Wed, 30 Dec 2020 12:42:33 +0000 Matthew Wilcox <willy@infradead.org> wrote:
> 
> > On Wed, Dec 30, 2020 at 07:40:14PM +0800, Hui Su wrote:
> > > local variable node_order do not need the static here.
> > 
> > It bloody well does.  It can be up to 2^10 entries on x86 (and larger
> > on others) That's 4kB which you've now moved onto the stack.
> 
> That being said, could we kmalloc the scratch area in
> __build_all_zonelists()?  And maybe remove that static spinlock?

I am not sure we can (e.g. early init code) but even if we could, what
would be an advantage. This code is called very seldom with a very
shallow stacks so using the stack allocation sounds like the easiest
thing to do.

> (what blocks node and cpu hotplug in there??)

Memory hotplug is excluded by the caller when it matters (e.g. no
locking for the early init).
-- 
Michal Hocko
SUSE Labs