linux-kernel - Re: [PATCH 08/17] mm/filemap: add read support for RWF

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Message-ID: <5c6b9c45-25fd-4a6a-bfcd-781431f5c6e0@kernel.dk>
Date: Fri, 15 Nov 2024 08:01:34 -0700
From: Jens Axboe <axboe@...nel.dk>
To: "Kirill A. Shutemov" <kirill@...temov.name>
Cc: linux-mm@...ck.org, linux-fsdevel@...r.kernel.org, hannes@...xchg.org,
 clm@...a.com, linux-kernel@...r.kernel.org, willy@...radead.org,
 linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org,
 linux-xfs@...r.kernel.org, bfoster@...hat.com
Subject: Re: [PATCH 08/17] mm/filemap: add read support for RWF_UNCACHED

On 11/15/24 1:49 AM, Kirill A. Shutemov wrote:
> On Thu, Nov 14, 2024 at 08:25:12AM -0700, Jens Axboe wrote:
>> @@ -2595,6 +2601,20 @@ static inline bool pos_same_folio(loff_t pos1, loff_t pos2, struct folio *folio)
>>  	return (pos1 >> shift == pos2 >> shift);
>>  }
>>  
>> +static void filemap_uncached_read(struct address_space *mapping,
>> +				  struct folio *folio)
>> +{
>> +	if (!folio_test_uncached(folio))
>> +		return;
>> +	if (folio_test_writeback(folio))
>> +		return;
> 
> Do we want to drop out here if the folio is dirty, but not yet under
> writeback?
> 
> It is checked inside folio_unmap_invalidate(), but we will lose
> PG_uncached if we get there.

True, seems prudent to skip if it's dirty as well, if only to avoid
losing uncached for that particular case. I'll add the tweak, thanks.

-- 
Jens Axboe