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Message-ID: <ed072ac6-cc70-9070-4e9d-281b9b60c9a6@linux.alibaba.com>
Date:   Fri, 24 Jun 2022 16:52:34 +0800
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Subject: Re: [RFC PATCH v2 2/3] mm: Add PUD level pagetable account
To:     Matthew Wilcox <willy@infradead.org>,
        Mike Rapoport <rppt@linux.ibm.com>
Cc:     akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <cover.1655887440.git.baolin.wang@linux.alibaba.com>
 <f7b2a6f6f5dfecbcac07fa3e187f10860c3a39ee.1655887440.git.baolin.wang@linux.alibaba.com>
 <YrMpZlQHMuCy06/m@linux.ibm.com> <YrRqhj3p/KKU73f1@casper.infradead.org>
From:   Baolin Wang <baolin.wang@linux.alibaba.com>
In-Reply-To: <YrRqhj3p/KKU73f1@casper.infradead.org>
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On 6/23/2022 9:28 PM, Matthew Wilcox wrote:
> On Wed, Jun 22, 2022 at 09:38:30AM -0500, Mike Rapoport wrote:
>> On Wed, Jun 22, 2022 at 04:58:53PM +0800, Baolin Wang wrote:
>>> +++ b/arch/loongarch/include/asm/pgalloc.h
>>> @@ -89,10 +89,15 @@ static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long address)
>>>   static inline pud_t *pud_alloc_one(struct mm_struct *mm, unsigned long address)
>>>   {
>>>   	pud_t *pud;
>>> +	struct page *pg;
>>
>> 	struct page *page;
>>
>> looks better IMO.
>>
>>> +
>>> +	pg = alloc_pages(GFP_KERNEL & ~__GFP_HIGHMEM, PUD_ORDER);
> 
> GFP_KERNEL does not include __GFP_HIGHMEM, so you can just use
> GFP_KERNEL here.

Yes. Thanks.

> 
>>> +	if (!pg)
>>> +		return NULL;
>>>   
>>> -	pud = (pud_t *) __get_free_pages(GFP_KERNEL, PUD_ORDER);
>>> -	if (pud)
>>> -		pud_init((unsigned long)pud, (unsigned long)invalid_pmd_table);
>>> +	pgtable_set_and_inc(pg);
>>> +	pud = (pud_t *)page_address(pg);
>>
>> I don't think __get_free_pages() should be replaced with alloc_pages()
>> here, just call pgtable_set_and_inc() with virt_to_page(pud).
> 
> I don't understand why you want that.  Take a look at the implementation
> of __get_free_pages().  Converting back to a struct page after calling
> that seems like a real waste of time to me.

IMO I have no strong preference. The code can be simpler with using 
__get_free_pages(), however like Matthew said it will add more conversion.