linux-kernel - Re: [PATCH] mm, page_alloc: drop pointless static qualifier in build

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Message-ID: <20191008192124.GT6681@dhcp22.suse.cz>
Date:   Tue, 8 Oct 2019 21:21:24 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Christopher Lameter <cl@...ux.com>
Cc:     Kaitao Cheng <pilgrimtao@...il.com>, akpm@...ux-foundation.org,
        sashal@...nel.org, osalvador@...e.de, mgorman@...hsingularity.net,
        rppt@...ux.ibm.com, dan.j.williams@...el.com,
        alexander.h.duyck@...ux.intel.com, pavel.tatashin@...rosoft.com,
        glider@...gle.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Muchun Song <smuchun@...il.com>
Subject: Re: [PATCH] mm, page_alloc: drop pointless static qualifier in
 build_zonelists()

On Tue 08-10-19 19:06:57, Cristopher Lameter wrote:
> On Sat, 28 Sep 2019, Kaitao Cheng wrote:
> 
> > There is no need to make the 'node_order' variable static
> > since new value always be assigned before use it.
> 
> In the past MAX_NUMMNODES could become quite large like 512 or 1k. Large
> array allocations on the stack are problematic.
> 
> Maybe that is no longer the case?

CONFIG_NODES_SHIFT=10 is nothing really unusual in distribution kernels.
Likely wasteful for most HW available but a proper way to address it in
this particular case is to use a different data structure than drop the
static modifier which seems to be more of an misunderstanding than an
intention.
-- 
Michal Hocko
SUSE Labs