linux-kernel - Re: [PATCH RFC 2/7] filemap: Change mapping_set_folio_min_order() -> mapping_set_folio

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Date: Fri, 26 Apr 2024 09:02:31 +0100
From: John Garry <john.g.garry@...cle.com>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
Cc: axboe@...nel.dk, brauner@...nel.org, djwong@...nel.org,
        viro@...iv.linux.org.uk, jack@...e.cz, akpm@...ux-foundation.org,
        willy@...radead.org, dchinner@...hat.com, tytso@....edu, hch@....de,
        martin.petersen@...cle.com, nilay@...ux.ibm.com, ritesh.list@...il.com,
        mcgrof@...nel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        ojaswin@...ux.ibm.com, p.raghav@...sung.com, jbongio@...gle.com,
        okiselev@...zon.com
Subject: Re: [PATCH RFC 2/7] filemap: Change mapping_set_folio_min_order() ->
 mapping_set_folio_orders()

On 25/04/2024 15:47, Pankaj Raghav (Samsung) wrote:
> On Mon, Apr 22, 2024 at 02:39:18PM +0000, John Garry wrote:
>> Borrowed from:
>>
>> https://urldefense.com/v3/__https://lore.kernel.org/linux-fsdevel/20240213093713.1753368-2-kernel@pankajraghav.com/__;!!ACWV5N9M2RV99hQ!LvajFab0xQx8oBWDlDtVY8duiLDjOKX91G4YqadoCu6gqatA2H0FzBUvdSC69dqXNoe2QvStSwrxIZ142MXOKk8$
>> (credit given in due course)
>>
>> We will need to be able to only use a single folio order for buffered
>> atomic writes, so allow the mapping folio order min and max be set.
> 
>>
>> We still have the restriction of not being able to support order-1
>> folios - it will be required to lift this limit at some stage.
> 
> This is already supported upstream for file-backed folios:
> commit: 8897277acfef7f70fdecc054073bea2542fc7a1b

ok

> 
>> index fc8eb9c94e9c..c22455fa28a1 100644
>> --- a/include/linux/pagemap.h
>> +++ b/include/linux/pagemap.h
>> @@ -363,9 +363,10 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
>>   #endif
>>   
>>   /*
>> - * mapping_set_folio_min_order() - Set the minimum folio order
>> + * mapping_set_folio_orders() - Set the minimum and max folio order
> 
> In the new series (sorry forgot to CC you),

no worries, I saw it

> I added a new helper called
> mapping_set_folio_order_range() which does something similar to avoid
> confusion based on willy's suggestion:
> https://urldefense.com/v3/__https://lore.kernel.org/linux-xfs/20240425113746.335530-3-kernel@pankajraghav.com/__;!!ACWV5N9M2RV99hQ!LvajFab0xQx8oBWDlDtVY8duiLDjOKX91G4YqadoCu6gqatA2H0FzBUvdSC69dqXNoe2QvStSwrxIZ14opzAoso$
> 

Fine, I can include that

> mapping_set_folio_min_order() also sets max folio order to be
> MAX_PAGECACHE_ORDER order anyway. So no need of explicitly calling it
> here?
> 

Here mapping_set_folio_min_order() is being replaced with 
mapping_set_folio_order_range(), so not sure why you mention that. 
Regardless, I'll use your mapping_set_folio_order_range().

>>   /**
>> @@ -400,7 +406,7 @@ static inline void mapping_set_folio_min_order(struct address_space *mapping,
>>    */
>>   static inline void mapping_set_large_folios(struct address_space *mapping)
>>   {
>> -	mapping_set_folio_min_order(mapping, 0);
>> +	mapping_set_folio_orders(mapping, 0, MAX_PAGECACHE_ORDER);
>>   }
>>   
>>   static inline unsigned int mapping_max_folio_order(struct address_space *mapping)
>> diff --git a/mm/filemap.c b/mm/filemap.c
>> index d81530b0aac0..d5effe50ddcb 100644
>> --- a/mm/filemap.c
>> +++ b/mm/filemap.c
>> @@ -1898,9 +1898,15 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
>>   no_page:
>>   	if (!folio && (fgp_flags & FGP_CREAT)) {
>>   		unsigned int min_order = mapping_min_folio_order(mapping);
>> -		unsigned int order = max(min_order, FGF_GET_ORDER(fgp_flags));
>> +		unsigned int max_order = mapping_max_folio_order(mapping);
>> +		unsigned int order = FGF_GET_ORDER(fgp_flags);
>>   		int err;
>>   
>> +		if (order > max_order)
>> +			order = max_order;
>> +		else if (order < min_order)
>> +			order = max_order;
> 
> order = min_order; ?

right

Thanks,
John