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Date:   Fri, 9 Sep 2022 20:44:52 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     David Hildenbrand <david@redhat.com>
Cc:     Miaohe Lin <linmiaohe@huawei.com>, akpm@linux-foundation.org,
        osalvador@suse.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 12/16] mm/page_alloc: use helper macro SZ_1{K,M}
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On Fri, Sep 09, 2022 at 01:34:52PM +0200, David Hildenbrand wrote:
> On 09.09.22 11:24, Miaohe Lin wrote:
> > @@ -9055,7 +9055,7 @@ void *__init alloc_large_system_hash(const char *tablename,
> >   		/* It isn't necessary when PAGE_SIZE >= 1MB */
> 
> Huh, how could we ever have that. Smells like dead code.
> 
> >   		if (PAGE_SHIFT < 20)
> 
> What about adjusting that as well? The it exactly matches the comment
> 
> if (PAGE_SIZE >= SZ_1M)
> 
> > -			numentries = round_up(numentries, (1<<20)/PAGE_SIZE);
> > +			numentries = round_up(numentries, SZ_1M / PAGE_SIZE);

The git history provides some clues here.  See a7e833182a92.
But we do have an architecture which has ...

#ifdef CONFIG_PAGE_SIZE_1MB
#define PAGE_SHIFT 20
#define HEXAGON_L1_PTE_SIZE __HVM_PDE_S_1MB
#endif

I don't think it's an especially common config.