linux-kernel - Re: drm + 4GB RAM + swiotlb = drm craps out

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Message-ID: <21d7e9970704012238x2c5e6c62hc30933d9575910cf@mail.gmail.com>
Date:	Mon, 2 Apr 2007 15:38:48 +1000
From:	"Dave Airlie" <airlied@...il.com>
To:	"Andi Kleen" <andi@...stfloor.org>
Cc:	"David Miller" <davem@...emloft.net>, linux-kernel@...r.kernel.org,
	dri-devel@...ts.sourceforge.net
Subject: Re: drm + 4GB RAM + swiotlb = drm craps out

> >
> > On a 64-bit machine GFP_KERNEL can give me any memory... it all works
> > fine on 32-bit highmem kernel as I don't get highmem... I really need
> > __GFP_DMA32 memory but we don't have a generic allocator that gives
> > this out that I can see..
>
> __get_free_pages(..., __GFP_DMA32) on 64bit or __GFP_KERNEL or i386
> (only gives you ~900MB)

Doesn't __get_free_pages give me physically linear memory, which while
nice it isn't essential for what I need, so if I can't get my full
allocation I could in theory just start to fallback down the orders
and calling it multiple times to actually get the amount of memory I
need, this just seems overly cumbersome when what I really want is
vmalloc_32 to just work correctly on 64-bit systems... (why doesn't
vmalloc_32 pass __GFP_DMA32 to the allocator????)

> Not sure what you mean? __alloc_pages never bounces by itself.
> The nearest you can get is __GFP_DMA/__GFP_DMA32, but these have
> their own 16MB/4GB zones and don't use the swiotlb pools. And of course it
> only gives you plain memory, but doesn't remap or copy anything.

Yes I want __GFP_DMA32 but I'd like it with vmalloc not with
__get_free_pages and I've no great need for physically linear page
allocations and as I'm after quite a large order I can see this
failing ... granted with a 4GB system maybe not that quickly..

Dave.
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