linux-kernel - Re: [PATCH] [0/13] General DMA zone rework

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Date:	Tue, 11 Mar 2008 19:49:26 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	"Luiz Fernando N. Capitulino" <lcapitulino@...driva.com.br>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] [0/13] General DMA zone rework

> | Oops. Thanks. I'll double check that. mask allocator indeed doesn't
> | handle __GFP_COMP and nobody should be passing that into dma_alloc_coherent
> | anyways. But the bug you got was for the small size wasn't it?
> 
>  No, it triggers the BUG_ON() which checks the gfp, not the one
> which checks MASK_MIN_SIZE.

I see. I misdiagnosed your original problem then. But fixing the 
size < 16 bytes case was a good idea anyways, someone else would
have triggered that.

> 
>  On the other hand I'm not sure whether it does the right thing
> (ie, pass size in bytes instead of order) it does:

> 
> """
> pg = get_order(size);
> [...]
> res = dma_alloc_coherent(dev, PAGE_SIZE << pg, dma, gfp_flags);

With the mask allocator it can be changed to pass size directly
and save some memory. Before that it didn't make any difference.

Can you perhaps send me a complete patch fixing that for sound and the 
__GFP_COMP with description and Signed-off-by etc.? I can add it to my 
patchkit then and you would be correctly attributed. Otherwise I can do it 
myself too if you prefer. I'll also do a grep over the tree for other
such bogus __GFP_COMP users. That was an issue I hadn't considered before.

> if (res != NULL)
> 	inc_snd_pages(pg);
> """
> 
>  Maybe it could be changed to:

Agreed.

-Andi

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