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

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Date: Tue, 26 Mar 2024 11:06:36 +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()

On 26/03/2024 11:00, Hannes Reinecke wrote:
> 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.
> 

I don't know understand what you mean by overly complicated. This conversion is standalone and it is
wrong to use folio_nr_pages after we `put` the folio. This patch just reworks the loop and in the
next patch I add min order support to readahead.

This patch doesn't depend on the next patch.

> Cheers,
> 
> Hannes
>