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Subject: Re: [PATCH 12/16] mm/page_alloc: use helper macro SZ_1{K,M}
To:     Matthew Wilcox <willy@infradead.org>,
        David Hildenbrand <david@redhat.com>
CC:     <akpm@linux-foundation.org>, <osalvador@suse.de>,
        <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
References: <20220909092451.24883-1-linmiaohe@huawei.com>
 <20220909092451.24883-13-linmiaohe@huawei.com>
 <f83025e2-d516-72f2-7053-4c5f9626dcf0@redhat.com>
 <YxuXtL83Z9NPj5uR@casper.infradead.org>
From:   Miaohe Lin <linmiaohe@huawei.com>
Message-ID: <eb1a4170-34e2-2db7-26a1-448e06f3a58b@huawei.com>
Date:   Tue, 13 Sep 2022 15:04:36 +0800
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On 2022/9/10 3:44, Matthew Wilcox wrote:
> 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)

Looks good. Will do it in next version.

>>
>>> -			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.

Maybe commit a7e833182a92 fixed a theoretical bug. But IMHO, it might be better to keep the code even
if no architecture defines PAGE_SIZE >= 1MB. These codes would be eliminated at compiling time. And
once there're architectures with PAGE_SIZE >= 1MB, we still work. Any thoughts? Thanks both.

Thanks,
Miaohe Lin