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Subject: Re: [PATCH v6 07/19] mm: Put readahead pages in cache earlier
To: Matthew Wilcox <willy@infradead.org>
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From: John Hubbard <jhubbard@nvidia.com>
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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.
> 
> 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, so after an initial look at patch 18's ("iomap: Convert from readpages to
readahead") use of readahead_page() and readahead_next(), I'm not sure what 
I'm missing. Seems like it would work...?

thanks,
-- 
John Hubbard
NVIDIA