linux-kernel - Re: [PATCH 2/3] x86, swiotlb: Try coherent allocations with __GFP

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Message-ID: <20150126115408.GE30345@8bytes.org>
Date:	Mon, 26 Jan 2015 12:54:08 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	Baoquan He <bhe@...hat.com>
Cc:	Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 2/3] x86, swiotlb: Try coherent allocations with
 __GFP_NOWARN

On Mon, Jan 26, 2015 at 11:22:36AM +0800, Baoquan He wrote:
> > Ok, so this practically does all allocations __GFP_NOWARN now. Shouldn't
> > you be doing this before swiotlb_alloc_coherent() and not before
> > dma_generic_alloc_coherent()?
> 
> I think this patch mainly suppress warning from buddy allocation
> failure because it tried buddy allocation several times before the final
> try of bounce buffer allocation. Buddy allocation failure will call
> dump_stack.

Yes, exactly. The default low-memory available to the page-allocator
with crashkernel=high is 8MB. This is up pretty fast and then we start
to get warnings, even when there is still memory left in the swiotlb
space. The __GFP_WARN is there to suppress the warnings from the
page-allocator, so it has to be set before it is called.


	Joerg

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