linux-kernel - Re: [PATCH 0/3] Early use of boot service memory

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Message-ID: <CAE9FiQW+kbq5Eu-ivu897ogQUGjwKy6jYO9hnxbKyuWqoaQgJQ@mail.gmail.com>
Date:	Mon, 18 Nov 2013 19:02:29 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>, Ingo Molnar <mingo@...nel.org>,
	jerry.hoemann@...com, Pekka Enberg <penberg@...nel.org>,
	Rob Landley <rob@...dley.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	x86 maintainers <x86@...nel.org>,
	Matt Fleming <matt.fleming@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"list@...ederm.org:DOCUMENTATION" <linux-doc@...r.kernel.org>,
	"list@...ederm.org:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
	linux-efi@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] Early use of boot service memory

On Mon, Nov 18, 2013 at 5:32 PM, H. Peter Anvin <hpa@...or.com> wrote:
> On 11/15/2013 10:30 AM, Vivek Goyal wrote:
>>
>> And IOMMU support is very flaky with kdump. And IOMMU's can be turned
>> off at command line. And that would force one to remove crahkernel_low=0.
>> So change of one command line option forces change of another. It is
>> complicated.
>>
>> Also there are very few systems which work with IOMMU on. A lot more
>> which work without IOMMU. We have all these DMAR issues and still nobody
>> has been able to address IOMMU issues properly.
>>
>
> Why do we need such a big bounce buffer for kdump swiotlb anyway?
> Surely the vast majority of all dump devices don't need it, so it is
> there for completeness, no?

Yes, because normal path will need that 64M+32k default.

We may reduce that amount to 16M or 18M and in second kernel let
allocate less for swiotlb.

Thanks

Yinghai
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