linux-kernel - Re: [PATCH v3 04/11] readahead: rework loop in page_cache_ra

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Date: Tue, 26 Mar 2024 10:44:02 +0100
From: Pankaj Raghav <kernel@...kajraghav.com>
To: Hannes Reinecke <hare@...e.de>, Matthew Wilcox <willy@...radead.org>
Cc: linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 gost.dev@...sung.com, chandan.babu@...cle.com, mcgrof@...nel.org,
 djwong@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 david@...morbit.com, akpm@...ux-foundation.org,
 Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [PATCH v3 04/11] readahead: rework loop in
 page_cache_ra_unbounded()

Hi Hannes,

On 26/03/2024 10:39, Hannes Reinecke wrote:
> On 3/25/24 19:41, Matthew Wilcox wrote:
>> On Wed, Mar 13, 2024 at 06:02:46PM +0100, Pankaj Raghav (Samsung) wrote:
>>> @@ -239,8 +239,8 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
>>>                * not worth getting one just for that.
>>>                */
>>>               read_pages(ractl);
>>> -            ractl->_index++;
>>> -            i = ractl->_index + ractl->_nr_pages - index - 1;
>>> +            ractl->_index += folio_nr_pages(folio);
>>> +            i = ractl->_index + ractl->_nr_pages - index;
>>>               continue;
>>>           }
>>>   @@ -252,13 +252,14 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
>>>               folio_put(folio);
>>>               read_pages(ractl);
>>>               ractl->_index++;
>>> -            i = ractl->_index + ractl->_nr_pages - index - 1;
>>> +            i = ractl->_index + ractl->_nr_pages - index;
>>>               continue;
>>>           }
>>
>> You changed index++ in the first hunk, but not the second hunk.  Is that
>> intentional?
> 
> Hmm. Looks you are right; it should be modified, too.
> Will be fixing it up.
> 
You initially had also in the second hunk:
ractl->index += folio_nr_pages(folio);

and I changed it to what it is now.

The reason is in my reply to willy:
https://lore.kernel.org/linux-xfs/s4jn4t4betknd3y4ltfccqxyfktzdljiz7klgbqsrccmv3rwrd@orlwjz77oyxo/

Let me know if you agree with it.

> Cheers,
> 
> Hannes
>