linux-kernel - Re: kdump broken on 2.6.37-rc4

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Date:	Thu, 16 Dec 2010 20:46:07 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Vivek Goyal <vgoyal@...hat.com>,
	Stanislaw Gruszka <sgruszka@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Maxim Uvarov <muvarov@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Neil Horman <nhorman@...hat.com>
Subject: Re: kdump broken on 2.6.37-rc4

On 12/16/2010 08:08 PM, H. Peter Anvin wrote:
> On 12/16/2010 07:58 PM, Yinghai wrote:
>> Please don't do that to 64 bit
>>
>> My big system with 1024g memory and a lot of cards with rhel 6 to make kdump work must have crashkernel=512m and second kernel need to take pci=nomsi
>>
>> Thanks
>>
> 
> Hm, this seems like an epic FAIL.
> 
> First of all, the current code still limits it to 896 MiB, so 512 MiB is
> not a significant restriction.

You only have chance to get 512M under 896M but not under 512M.

> 
> Second, this patch only applies if "crashkernel=" is not specified, so
> it doesn't even apply to your situation.
current code:
        /* 0 means: find the address automatically */
        if (crash_base <= 0) {
                const unsigned long long alignment = 16<<20;    /* 16M */

                /*
                 *  kexec want bzImage is below DEFAULT_BZIMAGE_ADDR_MAX
                 */
                crash_base = memblock_find_in_range(alignment,
                               DEFAULT_BZIMAGE_ADDR_MAX, crash_size, alignment);

                if (crash_base == MEMBLOCK_ERROR) {
                        pr_info("crashkernel reservation failed - No suitable area found.\n");
                        return;
                }
        } else {
                unsigned long long start;

                start = memblock_find_in_range(crash_base,
                                 crash_base + crash_size, crash_size, 1<<20);
                if (start != crash_base) {
                        pr_info("crashkernel reservation failed - memory is in use.\n");
                        return;
                }
        }

first branch : will take only crash_size.
second branch : will need to specify crash_base and crash_size.

> 
> Third, if you have to specify "crashkernel=" that means that there is
> yet another problem here that should be fixed.

no, every kdump need to specify crashkernel=128M or more.

	Yinghai
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