Re: RFA (Request for Advice): block/bio: get_user_pages() --> pin_user_pages()

[John Hubbard <jhubbard@nvidia.com>]

On 1/24/22 05:18, Matthew Wilcox wrote:
> On Sun, Jan 23, 2022 at 11:52:07PM -0800, John Hubbard wrote:
>> To ground this in reality, one of the partial call stacks is:
>>
>> do_direct_IO()
>>      dio_zero_block()
>>          page = ZERO_PAGE(0); <-- This is a problem
>>
>> I'm not sure what to use, instead of that zero page! The zero page
>> doesn't need to be allocated nor tracked, and so any replacement
>> approaches would need either other storage, or some horrid scheme that I
>> won't go so far as to write on the screen. :)
> 
> I'm not really sure what the problem is.
> 
> include/linux/mm.h:             is_zero_pfn(page_to_pfn(page));
> 
> and release_pages() already contains:
>                  if (is_huge_zero_page(page))
>                          continue;
> 
> Why can't the BIO release function contain an is_zero_pfn() check?

"OK." (With potential modifications as noted in the other thread with
Jan Kara and Chaitanya, we'll see.)

Thanks for responding with that answer so quickly, much appreciated!


thanks,
-- 
John Hubbard
NVIDIA