Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 28 Nov 2019 21:22:26 +0000
From:   Wei Yang <richard.weiyang@gmail.com>
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
Cc:     Wei Yang <richardw.yang@linux.intel.com>,
        akpm@linux-foundation.org, kirill.shutemov@linux.intel.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] mm/page_vma_mapped: use PMD_SIZE instead of
 calculating it
Message-ID: <20191128212226.sfrhfs5m3q7m6tly@master>
Reply-To: Wei Yang <richard.weiyang@gmail.com>
References: <20191128010321.21730-1-richardw.yang@linux.intel.com>
 <20191128083255.ab5rwj7gvktwunik@box.shutemov.name>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20191128083255.ab5rwj7gvktwunik@box.shutemov.name>
User-Agent: NeoMutt/20170113 (1.7.2)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Nov 28, 2019 at 11:32:55AM +0300, Kirill A. Shutemov wrote:
>On Thu, Nov 28, 2019 at 09:03:20AM +0800, Wei Yang wrote:
>> At this point, we are sure page is PageTransHuge, which means
>> hpage_nr_pages is HPAGE_PMD_NR.
>> 
>> This is safe to use PMD_SIZE instead of calculating it.
>> 
>> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
>> ---
>>  mm/page_vma_mapped.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
>> index eff4b4520c8d..76e03650a3ab 100644
>> --- a/mm/page_vma_mapped.c
>> +++ b/mm/page_vma_mapped.c
>> @@ -223,7 +223,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
>>  			if (pvmw->address >= pvmw->vma->vm_end ||
>>  			    pvmw->address >=
>>  					__vma_address(pvmw->page, pvmw->vma) +
>> -					hpage_nr_pages(pvmw->page) * PAGE_SIZE)
>> +					PMD_SIZE)
>>  				return not_found(pvmw);
>>  			/* Did we cross page table boundary? */
>>  			if (pvmw->address % PMD_SIZE == 0) {
>
>It is dubious cleanup. Maybe page_size(pvmw->page) instead? It will not
>break if we ever get PUD THP pages.
>

Thanks for your comment.

I took a look into the code again and found I may miss something.

I found we support PUD THP pages, whilc hpage_nr_pages() just return
HPAGE_PMD_NR on PageTransHuge. Why this is not possible to return PUD number?

Search in the kernel tree, one implementation of PUD_SIZE fault is
dev_dax_huge_fault. If page fault happens here, would this if break the loop
too early?

>-- 
> Kirill A. Shutemov

-- 
Wei Yang
Help you, Help me