Re: The usage of page_mapping() in architecture code

["Huang\, Ying" <ying.huang@intel.com>]

Hi, Russell,

Russell King - ARM Linux <linux@armlinux.org.uk> writes:

> On Sun, Feb 11, 2018 at 02:43:39PM +0800, Huang, Ying wrote:
[snip]
>> 
>> 
>> if page is an anonymous page in swap cache, "mapping &&
>> !mapping_mapped()" will be true, so we will delay flushing.  But if my
>> understanding of the code were correct, we should call
>> flush_kernel_dcache() because the kernel may access the page during
>> swapping in/out.
>> 
>> The code in other architectures follow the similar logic.  Would it be
>> better for page_mapping() here to return NULL for anonymous pages even
>> if they are in swap cache?  Of course we need to change the function
>> name.  page_file_mapping() appears a good name, but that has been used
>> already.  Any suggestion?
>
> flush_dcache_page() does nothing for anonymous pages (see cachetlb.txt,
> it's only defined to do anything for page cache pages.)
>
> flush_anon_page() deals with anonymous pages.

Thanks for your information!  But I found this isn't followed exactly in
the code.  For example, in get_mergeable_page() in mm/ksm.c,

	if (PageAnon(page)) {
		flush_anon_page(vma, page, addr);
		flush_dcache_page(page);
	} else {
		put_page(page);

flush_dcache_page() is called for anonymous pages too.

Best Regards,
Huang, Ying

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