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

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Date: Tue, 26 Mar 2024 11:00:26 +0100
From: Hannes Reinecke <hare@...e.de>
To: Pankaj Raghav <kernel@...kajraghav.com>,
 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()

On 3/26/24 10:44, Pankaj Raghav wrote:
> 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.
> 
Bah. That really is overly complicated. When we attempt a conversion 
that conversion should be stand-alone, not rely on some other patch 
modifications later on.
We definitely need to work on that to make it easier to review, even
without having to read the mail thread.

Cheers,

Hannes