linux-kernel - Re: How could we get rid of saved_max

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Message-ID: <20140221081806.GB1635@dhcp-16-105.nay.redhat.com>
Date:	Fri, 21 Feb 2014 16:18:06 +0800
From:	Baoquan He <bhe@...hat.com>
To:	Jon Mason <jdmason@...zu.us>
Cc:	WANG Chao <chaowang@...hat.com>, Muli Ben-Yehuda <muli@...ibm.com>,
	discuss@...-64.org, x86@...nel.org, kexec@...ts.infradead.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Yinghai Lu <yinghai@...nel.org>,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: How could we get rid of saved_max_pfn for calgary iommu?

On 02/19/14 at 05:04pm, Jon Mason wrote:
> On Tue, Feb 18, 2014 at 11:18 PM, WANG Chao <chaowang@...hat.com> wrote:
> > Hi, All
> >
> > arch/x86/kernel/pci-calgary.c is the only user of saved_max_pfn today:
> >
> > int __init detect_calgary(void)
> > {
> >         [..]
> >         specified_table_size = determine_tce_table_size((is_kdump_kernel() ?
> >                                         saved_max_pfn : max_pfn) * PAGE_SIZE);
> >         [..]
> > }
> 
> IIUC, the purpose of this code is to reuse the TCE table from the
> previous kernel.  Thus, it needs to be of the same size as the
> pre-kdump kernel.  It is using the max_pfn to determine the TCE table
> size in the non-kdump case.  If there is another way to determine the
> size it used before, then I am fine making the change to use that way.

>From code the size is from 64K to 8M, saved_max_pfn is needed to get
this. Could it be a fixed size for TCE table? If this can be a fixed
value, E.g 8M,  saved_max_pfn will be not needed any more though a
little memory may be wasted if total ram is smaller than 4G.

Baoquan
Thanks
> 
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