linux-kernel - Re: [PATCH] readahead: Use folio_nr_pages() instead of shift operation

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Message-ID: <1d515808-6589-4aa1-a363-f16bb6209b36@arm.com>
Date: Mon, 14 Jul 2025 08:54:36 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Andrew Morton <akpm@...ux-foundation.org>,
 Chi Zhiling <chizhiling@....com>
Cc: David Hildenbrand <david@...hat.com>, willy@...radead.org,
 linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Chi Zhiling <chizhiling@...inos.cn>
Subject: Re: [PATCH] readahead: Use folio_nr_pages() instead of shift
 operation

On 12/07/2025 23:25, Andrew Morton wrote:
> On Sat, 12 Jul 2025 10:23:32 +0800 Chi Zhiling <chizhiling@....com> wrote:
> 
>> On 2025/7/12 00:15, David Hildenbrand wrote:
>>> On 10.07.25 08:04, Chi Zhiling wrote:
>>>> From: Chi Zhiling <chizhiling@...inos.cn>
>>>>
>>>> folio_nr_pages() is faster helper function to get the number of pages
>>>> when NR_PAGES_IN_LARGE_FOLIO is enabled.
>>>>
>>>> Signed-off-by: Chi Zhiling <chizhiling@...inos.cn>
>>>> ---
>>>>   mm/readahead.c | 2 +-
>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/mm/readahead.c b/mm/readahead.c
>>>> index 95a24f12d1e7..406756d34309 100644
>>>> --- a/mm/readahead.c
>>>> +++ b/mm/readahead.c
>>>> @@ -649,7 +649,7 @@ void page_cache_async_ra(struct readahead_control 
>>>> *ractl,
>>>>        * Ramp up sizes, and push forward the readahead window.
>>>>        */
>>>>       expected = round_down(ra->start + ra->size - ra->async_size,
>>>> -            1UL << folio_order(folio));
>>>> +            folio_nr_pages(folio));
>>>>       if (index == expected) {
>>>>           ra->start += ra->size;
>>>>           /*
>>>
>>> This should probably get squashed in Ryans commit?
>>
>> I have no objection, it's up to Ryan.
> 
> "Ryans commit" is now c4602f9fa77f ("mm/readahead: store folio order in
> struct file_ra_state") in mm-stable.  I'd prefer not to rebase for this!
> 

Sorry about that... the function was previously using foilio_order() and storing
in a local variable and using it in 2 places, one of which was "1UL << order".
Because the other user went away I just moved the folio_order() call inline. But
agree folio_nr_pages() is better. FWIW:

Reviewed-by: Ryan Roberts <ryan.roberts@....com>