Re: [PATCH v2] mm: honor FGP_NOWAIT for page cache page allocation

[Jens Axboe <axboe@kernel.dk>]

On 7/3/22 2:37 AM, Matthew Wilcox wrote:
> On Sat, Jul 02, 2022 at 09:43:32AM -0600, Jens Axboe wrote:
>> +++ b/mm/filemap.c
>> @@ -1988,6 +1988,10 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
>>  			gfp |= __GFP_WRITE;
>>  		if (fgp_flags & FGP_NOFS)
>>  			gfp &= ~__GFP_FS;
>> +		if (fgp_flags & FGP_NOWAIT) {
>> +			gfp &= ~GFP_KERNEL;
>> +			gfp |= GFP_NOWAIT | __GFP_NOWARN;
>> +		}
> 
> Wouldn't it be simpler to write:
> 
> 		if (fgp_flags & FGP_NOWAIT) {
> 			gfp &= ~__GFP_DIRECT_RECLAIM;
> 			gfp |= __GFP_NOWARN;
> 		}

That won't clear IO or FS, though? We really just want GFP_NOWAIT |
__GFP_NOWARN here, but didn't want to make assumptions on whatever else
would be set in gfp already.

> (I'd prefer it if the caller passed in the GFP flags that it actually
> wants, but looking at the patches that prompted this, that seems rather
> annoying to do)

Yes me too, but that's a lot of annoying churn...

-- 
Jens Axboe