Re: [PATCH v6 07/19] mm: Put readahead pages in cache earlier

John Hubbard
2020-02-19T01:13:11Z

On 2/18/20 5:02 PM, Matthew Wilcox wrote:
> On Tue, Feb 18, 2020 at 04:01:43PM -0800, John Hubbard wrote:
>> How about this instead? It uses the "for" loop fully and more naturally,
>> and is easier to read. And it does the same thing:
>>
>> static inline struct page *readahead_page(struct readahead_control *rac)
>> {
>> struct page *page;
>>
>> if (!rac->_nr_pages)
>> return NULL;
>>
>> page = xa_load(&rac->mapping->i_pages, rac->_start);
>> VM_BUG_ON_PAGE(!PageLocked(page), page);
>> rac->_batch_count = hpage_nr_pages(page);
>>
>> return page;
>> }
>>
>> static inline struct page *readahead_next(struct readahead_control *rac)
>> {
>> rac->_nr_pages -= rac->_batch_count;
>> rac->_start += rac->_batch_count;
>>
>> return readahead_page(rac);
>> }
>>
>> #define readahead_for_each(rac, page) \
>> for (page = readahead_page(rac); page != NULL; \
>> page = readahead_page(rac))
>
> I'm assuming you mean 'page = readahead_next(rac)' on that second line.

Yep. :)

>
> If you keep reading all the way to the penultimate patch, it won't work
> for iomap ... at least not in the same way.
>

OK, getting there...

thanks,
--
John Hubbard
NVIDIA