linux-kernel - Re: [PATCH 04/13] mm/readahead: add readahead

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Message-ID: <ca1f78bb-47e2-424b-a57e-f3272b1450cf@kernel.dk>
Date: Fri, 8 Nov 2024 12:22:59 -0700
From: Jens Axboe <axboe@...nel.dk>
To: Matthew Wilcox <willy@...radead.org>
Cc: linux-mm@...ck.org, linux-fsdevel@...r.kernel.org, hannes@...xchg.org,
 clm@...a.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/13] mm/readahead: add readahead_control->uncached
 member

On 11/8/24 11:21 AM, Matthew Wilcox wrote:
> On Fri, Nov 08, 2024 at 10:43:27AM -0700, Jens Axboe wrote:
>> +++ b/mm/readahead.c
>> @@ -191,7 +191,13 @@ static void read_pages(struct readahead_control *rac)
>>  static struct folio *ractl_alloc_folio(struct readahead_control *ractl,
>>  				       gfp_t gfp_mask, unsigned int order)
>>  {
>> -	return filemap_alloc_folio(gfp_mask, order);
>> +	struct folio *folio;
>> +
>> +	folio = filemap_alloc_folio(gfp_mask, order);
>> +	if (folio && ractl->uncached)
>> +		folio_set_uncached(folio);
> 
> If we've just allocated it, it should be safe to use
> __folio_set_uncached() here, no?

Indeed, we can use __folio_set_uncached() here. I'll make that change.

> Not that I'm keen on using a folio flag here, but I'm reserving judgement
> on that unti I've got further through this series and see how it's used.
> I can see that it might be necessary.

I knew that'd be one of the more contentious items here... On the read
side, we can get by without the flag. But for writeback we do need it.
I just kept it consistent and used folio_*_uncached() throughout
because of that.

-- 
Jens Axboe