Date:   Tue, 14 Feb 2023 13:44:06 +0200
From:   Mike Rapoport <rppt@kernel.org>
To:     David Hildenbrand <david@redhat.com>
Cc:     Qi Zheng <zhengqi.arch@bytedance.com>,
        Qi Zheng <arch0.zheng@gmail.com>,
        Vlastimil Babka <vbabka@suse.cz>, akpm@linux-foundation.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Teng Hu <huteng.ht@bytedance.com>,
        Matthew Wilcox <willy@infradead.org>,
        Mel Gorman <mgorman@techsingularity.net>,
        Oscar Salvador <osalvador@suse.de>,
        Muchun Song <muchun.song@linux.dev>
Subject: Re: [PATCH] mm: page_alloc: don't allocate page from memoryless nodes
Message-ID: <Y+t0Bhu7BCzH2Dp4@kernel.org>
References: <20230212110305.93670-1-zhengqi.arch@bytedance.com>
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 <eefc40e5-a14b-22c5-3480-6786afa1c8f4@redhat.com>
 <Y+tXrK/g1Nrd/q1h@kernel.org>
 <67240e55-af49-f20a-2b4b-b7d574cd910d@gmail.com>
 <22f0e262-982e-ea80-e52a-a3c924b31d58@redhat.com>
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(added x86 folks)

On Tue, Feb 14, 2023 at 12:29:42PM +0100, David Hildenbrand wrote:
> On 14.02.23 12:26, Qi Zheng wrote:
> > On 2023/2/14 19:22, David Hildenbrand wrote:
> > > 
> > > TBH, this is the first time I hear of NODE_MIN_SIZE and it seems to be a
> > > pretty x86 specific thing.
> > > 
> > > Are we sure we want to get NODE_MIN_SIZE involved?
> > 
> > Maybe add an arch_xxx() to handle it?
> 
> I still haven't figured out what we want to achieve with NODE_MIN_SIZE at
> all. It smells like an arch-specific hack looking at
> 
> "Don't confuse VM with a node that doesn't have the minimum amount of
> memory"
> 
> Why shouldn't mm-core deal with that?

Well, a node with <4M RAM is not very useful and bears all the overhead of
an extra live node.

But, hey, why won't we just drop that '< NODE_MIN_SIZE' and let people with
weird HW configurations just live with this?
 
> I'd appreciate an explanation of the bigger picture, what the issue is and
> what the approach to solve it is (including memory onlining/offlining).
> 
> -- 
> Thanks,
> 
> David / dhildenb
> 

-- 
Sincerely yours,
Mike.