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From: Yinghai Lu <yinghai@kernel.org>
To: Rob Landley <rob@landley.net>
Cc: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org,
	ebiederm@xmission.com, tglx@linutronix.de, hpa@linux.intel.com,
	linux-tip-commits@vger.kernel.org
Subject: Re: [tip:x86/mm2] x86: Add Crash kernel low reservation
Date: Wed, 6 Feb 2013 22:39:32 -0800	[thread overview]
Message-ID: <CAE9FiQV9cAjH1b3rJvFqDaiaEiXaaiG50-Ap_tcvTMb_GV6o2w@mail.gmail.com> (raw)
In-Reply-To: <1360214087.12062.21@driftwood>

On Wed, Feb 6, 2013 at 9:14 PM, Rob Landley <rob@landley.net> wrote:
> Yeah yeah, I'm behind on email...
>
>
> On 01/29/2013 07:51:25 PM, tip-bot for Yinghai Lu wrote:
>>
>> Commit-ID:  2cde8ae169982ad1d1023ac628bb54053d0e9d4d
>> Gitweb:
>> http://git.kernel.org/tip/2cde8ae169982ad1d1023ac628bb54053d0e9d4d
>> Author:     Yinghai Lu <yinghai@kernel.org>
>> AuthorDate: Thu, 24 Jan 2013 12:20:11 -0800
>> Committer:  H. Peter Anvin <hpa@linux.intel.com>
>> CommitDate: Tue, 29 Jan 2013 15:31:59 -0800
>>
>> x86: Add Crash kernel low reservation
>>
>> During kdump kernel's booting stage, it need to find low ram for
>> swiotlb buffer when system does not support intel iommu/dmar remapping.
>>
>> kexed-tools is appending memmap=exactmap and range from /proc/iomem
>> with "Crash kernel", and that range is above 4G for 64bit after boot
>> protocol 2.12.
>>
>> We need to add another range in /proc/iomem like "Crash kernel low",
>> so kexec-tools could find that info and append to kdump kernel
>> command line.
>>
>> User could specify the size with crashkernel_low=XX[KMG].
>>
>> -v2: fix warning that is found by Fengguang's test robot.
>> -v3: move out get_mem_size change to another patch, to solve compiling
>>      warning that is found by Borislav Petkov <bp@alien8.de>
>> -v4: user must specify crashkernel_low if system does not support
>>      intel or amd iommu.
>
>
> I missed: why can we not autodetect the lack of support and DTRT?

We need to process crashkernel early, and at that time we can not find out if
we can get iommu initialized properly.

>
>
>> Signed-off-by: Yinghai Lu <yinghai@kernel.org>
>> Link:
>> http://lkml.kernel.org/r/1359058816-7615-31-git-send-email-yinghai@kernel.org
>> Cc: Eric Biederman <ebiederm@xmission.com>
>> Cc: Rob Landley <rob@landley.net>
>> Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
>> ---
>>  Documentation/kernel-parameters.txt |  3 +++
>>  arch/x86/kernel/setup.c             | 42
>> +++++++++++++++++++++++++++++++++++--
>>  include/linux/kexec.h               |  3 +++
>>  kernel/kexec.c                      | 34 +++++++++++++++++++++++++-----
>>  4 files changed, 75 insertions(+), 7 deletions(-)
>>
>> diff --git a/Documentation/kernel-parameters.txt
>> b/Documentation/kernel-parameters.txt
>> index 363e348..da0e077 100644
>> --- a/Documentation/kernel-parameters.txt
>> +++ b/Documentation/kernel-parameters.txt
>> @@ -594,6 +594,9 @@ bytes respectively. Such letter suffixes can also be
>> entirely omitted.
>>                         is selected automatically. Check
>>                         Documentation/kdump/kdump.txt for further details.
>>
>> +       crashkernel_low=size[KMG]
>> +                       [KNL, x86] parts under 4G.
>> +
>>         crashkernel=range1:size1[,range2:size2,...][@offset]
>>                         [KNL] Same as above, but depends on the memory
>>                         in the running system. The syntax of range is
>
>
> I don't understand this documentation.

Looks better if crashkernel_low is moved under crashkernel.

>
> The "parts under 4G." assumes you understand the context of this posting
> which isn't going into the docs. Above you say:
>
>
>> Try to reserve some under 4G if the normal "Crash kernel" is above 4G.
>
>
> Which is much clearer. Adding this in the middle also makes the "Same as
> above" slightly confusing (you have two different aboves...)
>
> The first version (crashkernel=onesize) strongly implies the reservation is
> physically contiguous. The comma separated version implies that there are
> discontiguous reservations, manually specified.
>
> So is crashkernel_low=size a separate reservation from crashkernel=size, or
> a modifier on the existing contiguous allocation? Do you still need a
> crashkernel= entry if you've got a crashkernel_low= entry? If you can (or
> are required to) specify both, is one a constraint on part of the other or
> it an addition (so it reserves crashkernel+crashkernel_low)? I seems
> unlikely "parts under 4G" means it's trying to make one contiguous
> reservation straddle the high/low boundary to put parts in each while still
> being contiguous...
>
> I have no idea from what you've added to kernel-parameters.txt.
>
> Looking at the code, I _think_ this adds an additional independent
> reservation. I.E. crashkernel=size says "allocate memory from anywhere",
> crashkernel_low=size says "allocate memory from low memory", and doing both
> allocates two chunks like the comma separated version.

comma separated version only allocate one piece, right?

The syntax is:

    crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset]
    range=start-[end]

    'start' is inclusive and 'end' is exclusive.

For example:

    crashkernel=512M-2G:64M,2G-:128M

This would mean:

    1) if the RAM is smaller than 512M, then don't reserve anything
       (this is the "rescue" case)
    2) if the RAM size is between 512M and 2G (exclusive), then reserve 64M
    3) if the RAM size is larger than 2G, then reserve 128M

>
> Oh well. It's not hugely important that I understand a subsystem I don't
> use, but having to look at the code to figure out what the documentation is
> saying makes me uncomfortable.

logic for crashkernel_low, if crashkernel allocate above 4G, and will continue
allocate ram under 4G as user specified with crashkernel_low.

Yinghai

  reply	other threads:[~2013-02-07  6:39 UTC|newest]

Thread overview: 89+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-01-24 20:19 [PATCH 00/35] x86, boot, 64bit: Add support for loading ramdisk and bzImage above 4G Yinghai Lu
2013-01-24 20:19 ` [PATCH 01/35] x86, mm: Fix page table early allocation offset checking Yinghai Lu
2013-01-30  1:20   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-24 20:19 ` [PATCH 02/35] x86: Handle multiple exactmaps and out of order exactmap Yinghai Lu
2013-01-24 20:19 ` [PATCH 03/35] x86, mm: Introduce memmap=reserveram Yinghai Lu
2013-01-24 20:19 ` [PATCH 04/35] x86: Clean up e820 add kernel range Yinghai Lu
2013-01-24 23:21   ` Jacob Shin
2013-01-30  1:21   ` [tip:x86/mm2] x86: Factor out e820_add_kernel_range() tip-bot for Yinghai Lu
2013-01-24 20:19 ` [PATCH 05/35] x86, 64bit, mm: Make pgd next calculation consistent with pud/pmd Yinghai Lu
2013-01-30  1:22   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-24 20:19 ` [PATCH 06/35] x86, realmode: Set real_mode permissions early Yinghai Lu
2013-01-30  1:23   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-24 20:19 ` [PATCH 07/35] x86, 64bit, mm: Add generic kernel/ident mapping helper Yinghai Lu
2013-01-30  1:24   ` [tip:x86/mm2] x86, 64bit, mm: Add generic kernel/ ident " tip-bot for Yinghai Lu
2013-01-24 20:19 ` [PATCH 08/35] x86, 64bit: Copy zero-page early Yinghai Lu
2013-01-30  1:25   ` [tip:x86/mm2] x86, 64bit: Copy struct boot_params early tip-bot for Yinghai Lu
2013-01-24 20:19 ` [PATCH 09/35] x86, 64bit, realmode: Use init_level4_pgt to set trapmoline_pgd directly Yinghai Lu
2013-01-30  1:27   ` [tip:x86/mm2] x86, 64bit, realmode: Use init_level4_pgt to set trampoline_pgd directly tip-bot for Yinghai Lu
2013-01-24 20:19 ` [PATCH 10/35] x86, realmode: Separate real_mode reserve and setup Yinghai Lu
2013-01-30  1:28   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-24 20:19 ` [PATCH 11/35] x86, 64bit: early #PF handler set page table Yinghai Lu
2013-01-30  1:29   ` [tip:x86/mm2] x86, 64bit: Use a #PF handler to materialize early mappings on demand tip-bot for H. Peter Anvin
2013-01-24 20:19 ` [PATCH 12/35] x86, 64bit: #PF handler set page to cover only 2M per #PF Yinghai Lu
2013-01-30  1:30   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-24 20:19 ` [PATCH 13/35] x86, 64bit: Don't set max_pfn_mapped wrong value early on native path Yinghai Lu
2013-01-30  1:31   ` [tip:x86/mm2] x86, 64bit: Don' t " tip-bot for Yinghai Lu
2013-01-24 20:19 ` [PATCH 14/35] x86: Merge early_reserve_initrd for 32bit and 64bit Yinghai Lu
2013-01-30  1:32   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-24 20:19 ` [PATCH 15/35] x86: Add get_ramdisk_image/size() Yinghai Lu
2013-01-30  1:34   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-24 20:19 ` [PATCH 16/35] x86, boot: Add get_cmd_line_ptr() Yinghai Lu
2013-01-30  1:35   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-24 20:19 ` [PATCH 17/35] x86, boot: Move checking of cmd_line_ptr out of common path Yinghai Lu
2013-01-30  1:36   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-24 20:19 ` [PATCH 18/35] x86, boot: Pass cmd_line_ptr with unsigned long instead Yinghai Lu
2013-01-30  1:37   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-24 20:20 ` [PATCH 19/35] x86, boot: Move verify_cpu.S and no_longmode down Yinghai Lu
2013-01-30  1:38   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-24 20:20 ` [PATCH 20/35] x86, boot: Move lldt/ltr out of 64bit code section Yinghai Lu
2013-01-30  1:39   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-24 20:20 ` [PATCH 21/35] x86, kexec: Remove 1024G limitation for kexec buffer on 64bit Yinghai Lu
2013-01-30  1:40   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-24 20:20 ` [PATCH 22/35] x86, kexec: Set ident mapping for kernel that is above max_pfn Yinghai Lu
2013-01-30  1:42   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-24 20:20 ` [PATCH 23/35] x86, kexec: Replace ident_mapping_init and init_level4_page Yinghai Lu
2013-01-30  1:43   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-24 20:20 ` [PATCH 24/35] x86, kexec, 64bit: Only set ident mapping for ram Yinghai Lu
2013-01-30  1:44   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-24 20:20 ` [PATCH 25/35] x86, boot: Add fields to support load bzImage and ramdisk above 4G Yinghai Lu
2013-01-28  0:07   ` [tip:x86/boot] x86, boot: Define the 2.12 bzImage boot protocol tip-bot for H. Peter Anvin
2013-01-29  9:48   ` [tip:x86/boot] x86, boot: Sanitize boot_params if not zeroed on creation tip-bot for H. Peter Anvin
2013-01-30  1:45   ` [tip:x86/mm2] x86, boot: enable support load bzImage and ramdisk above 4G tip-bot for Yinghai Lu
2013-01-30  1:54     ` Yinghai Lu
2013-01-30  2:18       ` H. Peter Anvin
2013-01-30  3:47   ` [tip:x86/mm2] x86, boot: Support loading bzImage, boot_params " tip-bot for Yinghai Lu
2013-01-24 20:20 ` [PATCH 26/35] x86, boot: Update comments about entries for 64bit image Yinghai Lu
2013-01-30  1:46   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-30  3:48   ` tip-bot for Yinghai Lu
2013-01-24 20:20 ` [PATCH 27/35] x86, boot: Not need to check setup_header version for setup_data Yinghai Lu
2013-01-30  1:47   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-30  3:49   ` tip-bot for Yinghai Lu
2013-01-24 20:20 ` [PATCH 28/35] memblock: Add memblock_mem_size() Yinghai Lu
2013-01-30  1:49   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-30  3:50   ` tip-bot for Yinghai Lu
2013-01-24 20:20 ` [PATCH 29/35] x86, kdump: Remove crashkernel range find limit for 64bit Yinghai Lu
2013-01-30  1:50   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-30  3:51   ` tip-bot for Yinghai Lu
2013-01-24 20:20 ` [PATCH 30/35] x86: Add Crash kernel low reservation Yinghai Lu
2013-01-30  1:51   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-02-07  5:14     ` Rob Landley
2013-02-07  6:39       ` Yinghai Lu [this message]
2013-01-30  3:52   ` tip-bot for Yinghai Lu
2013-01-24 20:20 ` [PATCH 31/35] x86: Merge early kernel reserve for 32bit and 64bit Yinghai Lu
2013-01-30  1:52   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-30  3:53   ` tip-bot for Yinghai Lu
2013-01-24 20:20 ` [PATCH 32/35] x86, 64bit, mm: Mark data/bss/brk to nx Yinghai Lu
2013-01-30  1:53   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-30  3:55   ` tip-bot for Yinghai Lu
2013-01-24 20:20 ` [PATCH 33/35] x86, 64bit, mm: hibernate use generic mapping_init Yinghai Lu
2013-01-24 22:50   ` Rafael J. Wysocki
2013-01-30  1:54   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-30  3:56   ` tip-bot for Yinghai Lu
2013-01-24 20:20 ` [PATCH 34/35] mm: Add alloc_bootmem_low_pages_nopanic() Yinghai Lu
2013-01-30  1:56   ` [tip:x86/mm2] " tip-bot for Yinghai Lu
2013-01-30  3:57   ` tip-bot for Yinghai Lu
2013-01-24 20:20 ` [PATCH 35/35] x86: Don't panic if can not alloc buffer for swiotlb Yinghai Lu
2013-01-25 16:47   ` Konrad Rzeszutek Wilk
2013-01-30  1:57   ` [tip:x86/mm2] x86: Don' t " tip-bot for Yinghai Lu
2013-01-30  3:58   ` tip-bot for Yinghai Lu

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