Date:   Mon, 1 Jun 2020 16:59:01 -0500
From:   John Donnelly <john.p.donnelly@...cle.com>
To:     Bhupesh Sharma <bhsharma@...hat.com>
Cc:     Prabhakar Kushwaha <prabhakar.pkin@...il.com>,
        Chen Zhou <chenzhou10@...wei.com>,
        Simon Horman <horms@...ge.net.au>,
        Devicetree List <devicetree@...r.kernel.org>,
        Baoquan He <bhe@...hat.com>, Will Deacon <will@...nel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        kexec mailing list <kexec@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        guohanjun@...wei.com, James Morse <james.morse@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Prabhakar Kushwaha <pkushwaha@...vell.com>,
        RuiRui Yang <dyoung@...hat.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v8 0/5] support reserving crashkernel above 4G on arm64
 kdump

Hi .  See below ! 

> On Jun 1, 2020, at 4:02 PM, Bhupesh Sharma <bhsharma@...hat.com> wrote:
> 
> Hi John,
> 
> On Tue, Jun 2, 2020 at 1:01 AM John Donnelly <John.P.donnelly@...cle.com> wrote:
>> 
>> Hi,
>> 
>> 
>> On 6/1/20 7:02 AM, Prabhakar Kushwaha wrote:
>>> Hi Chen,
>>> 
>>> On Thu, May 21, 2020 at 3:05 PM Chen Zhou <chenzhou10@...wei.com> wrote:
>>>> This patch series enable reserving crashkernel above 4G in arm64.
>>>> 
>>>> There are following issues in arm64 kdump:
>>>> 1. We use crashkernel=X to reserve crashkernel below 4G, which will fail
>>>> when there is no enough low memory.
>>>> 2. Currently, crashkernel=Y@X can be used to reserve crashkernel above 4G,
>>>> in this case, if swiotlb or DMA buffers are required, crash dump kernel
>>>> will boot failure because there is no low memory available for allocation.
>>>> 
>>>> To solve these issues, introduce crashkernel=X,low to reserve specified
>>>> size low memory.
>>>> Crashkernel=X tries to reserve memory for the crash dump kernel under
>>>> 4G. If crashkernel=Y,low is specified simultaneously, reserve spcified
>>>> size low memory for crash kdump kernel devices firstly and then reserve
>>>> memory above 4G.
>>>> 
>>>> When crashkernel is reserved above 4G in memory, that is, crashkernel=X,low
>>>> is specified simultaneously, kernel should reserve specified size low memory
>>>> for crash dump kernel devices. So there may be two crash kernel regions, one
>>>> is below 4G, the other is above 4G.
>>>> In order to distinct from the high region and make no effect to the use of
>>>> kexec-tools, rename the low region as "Crash kernel (low)", and add DT property
>>>> "linux,low-memory-range" to crash dump kernel's dtb to pass the low region.
>>>> 
>>>> Besides, we need to modify kexec-tools:
>>>> arm64: kdump: add another DT property to crash dump kernel's dtb(see [1])
>>>> 
>>>> The previous changes and discussions can be retrieved from:
>>>> 
>>>> Changes since [v7]
>>>> - Move x86 CRASH_ALIGN to 2M
>>>> Suggested by Dave and do some test, move x86 CRASH_ALIGN to 2M.
>>>> - Update Documentation/devicetree/bindings/chosen.txt
>>>> Add corresponding documentation to Documentation/devicetree/bindings/chosen.txt suggested by Arnd.
>>>> - Add Tested-by from Jhon and pk
>>>> 
>>>> Changes since [v6]
>>>> - Fix build errors reported by kbuild test robot.
>>>> 
>>>> Changes since [v5]
>>>> - Move reserve_crashkernel_low() into kernel/crash_core.c.
>>>> - Delete crashkernel=X,high.
>>>> - Modify crashkernel=X,low.
>>>> If crashkernel=X,low is specified simultaneously, reserve spcified size low
>>>> memory for crash kdump kernel devices firstly and then reserve memory above 4G.
>>>> In addition, rename crashk_low_res as "Crash kernel (low)" for arm64, and then
>>>> pass to crash dump kernel by DT property "linux,low-memory-range".
>>>> - Update Documentation/admin-guide/kdump/kdump.rst.
>>>> 
>>>> Changes since [v4]
>>>> - Reimplement memblock_cap_memory_ranges for multiple ranges by Mike.
>>>> 
>>>> Changes since [v3]
>>>> - Add memblock_cap_memory_ranges back for multiple ranges.
>>>> - Fix some compiling warnings.
>>>> 
>>>> Changes since [v2]
>>>> - Split patch "arm64: kdump: support reserving crashkernel above 4G" as
>>>> two. Put "move reserve_crashkernel_low() into kexec_core.c" in a separate
>>>> patch.
>>>> 
>>>> Changes since [v1]:
>>>> - Move common reserve_crashkernel_low() code into kernel/kexec_core.c.
>>>> - Remove memblock_cap_memory_ranges() i added in v1 and implement that
>>>> in fdt_enforce_memory_region().
>>>> There are at most two crash kernel regions, for two crash kernel regions
>>>> case, we cap the memory range [min(regs[*].start), max(regs[*].end)]
>>>> and then remove the memory range in the middle.
>>>> 
>>>> [1]: https://urldefense.com/v3/__http://lists.infradead.org/pipermail/kexec/2020-May/025128.html__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbvpn1uM1$
>>>> [v1]: https://urldefense.com/v3/__https://lkml.org/lkml/2019/4/2/1174__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbt0xN9PE$
>>>> [v2]: https://urldefense.com/v3/__https://lkml.org/lkml/2019/4/9/86__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbub7yUQH$
>>>> [v3]: https://urldefense.com/v3/__https://lkml.org/lkml/2019/4/9/306__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbnc4zPPV$
>>>> [v4]: https://urldefense.com/v3/__https://lkml.org/lkml/2019/4/15/273__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbvsAsZLu$
>>>> [v5]: https://urldefense.com/v3/__https://lkml.org/lkml/2019/5/6/1360__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbl24n-79$
>>>> [v6]: https://urldefense.com/v3/__https://lkml.org/lkml/2019/8/30/142__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbs7r8G2a$
>>>> [v7]: https://urldefense.com/v3/__https://lkml.org/lkml/2019/12/23/411__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbiFUH90G$
>>>> 
>>>> Chen Zhou (5):
>>>>   x86: kdump: move reserve_crashkernel_low() into crash_core.c
>>>>   arm64: kdump: reserve crashkenel above 4G for crash dump kernel
>>>>   arm64: kdump: add memory for devices by DT property, low-memory-range
>>>>   kdump: update Documentation about crashkernel on arm64
>>>>   dt-bindings: chosen: Document linux,low-memory-range for arm64 kdump
>>>> 
>>> We are getting "warn_alloc" [1] warning during boot of kdump kernel
>>> with bootargs as [2] of primary kernel.
>>> This error observed on ThunderX2  ARM64 platform.
>>> 
>>> It is observed with latest upstream tag (v5.7-rc3) with this patch set
>>>  and https://urldefense.com/v3/__https://lists.infradead.org/pipermail/kexec/2020-May/025128.html__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbiIAAlzu$
>>> Also **without** this patch-set
>>> "https://urldefense.com/v3/__https://www.spinics.net/lists/arm-kernel/msg806882.html__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbjC6ujMA$"
>>> 
>>> This issue comes whenever crashkernel memory is reserved after 0xc000_0000.
>>> More details discussed earlier in
>>> https://urldefense.com/v3/__https://www.spinics.net/lists/arm-kernel/msg806882.html__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbjC6ujMA$  without any
>>> solution
>>> 
>>> This patch-set is expected to solve similar kind of issue.
>>> i.e. low memory is only targeted for DMA, swiotlb; So above mentioned
>>> observation should be considered/fixed. .
>>> 
>>> --pk
>>> 
>>> [1]
>>> [   30.366695] DMI: Cavium Inc. Saber/Saber, BIOS
>>> TX2-FW-Release-3.1-build_01-2803-g74253a541a mm/dd/yyyy
>>> [   30.367696] NET: Registered protocol family 16
>>> [   30.369973] swapper/0: page allocation failure: order:6,
>>> mode:0x1(GFP_DMA), nodemask=(null),cpuset=/,mems_allowed=0
>>> [   30.369980] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.7.0-rc3+ #121
>>> [   30.369981] Hardware name: Cavium Inc. Saber/Saber, BIOS
>>> TX2-FW-Release-3.1-build_01-2803-g74253a541a mm/dd/yyyy
>>> [   30.369984] Call trace:
>>> [   30.369989]  dump_backtrace+0x0/0x1f8
>>> [   30.369991]  show_stack+0x20/0x30
>>> [   30.369997]  dump_stack+0xc0/0x10c
>>> [   30.370001]  warn_alloc+0x10c/0x178
>>> [   30.370004]  __alloc_pages_slowpath.constprop.111+0xb10/0xb50
>>> [   30.370006]  __alloc_pages_nodemask+0x2b4/0x300
>>> [   30.370008]  alloc_page_interleave+0x24/0x98
>>> [   30.370011]  alloc_pages_current+0xe4/0x108
>>> [   30.370017]  dma_atomic_pool_init+0x44/0x1a4
>>> [   30.370020]  do_one_initcall+0x54/0x228
>>> [   30.370027]  kernel_init_freeable+0x228/0x2cc
>>> [   30.370031]  kernel_init+0x1c/0x110
>>> [   30.370034]  ret_from_fork+0x10/0x18
>>> [   30.370036] Mem-Info:
>>> [   30.370064] active_anon:0 inactive_anon:0 isolated_anon:0
>>> [   30.370064]  active_file:0 inactive_file:0 isolated_file:0
>>> [   30.370064]  unevictable:0 dirty:0 writeback:0 unstable:0
>>> [   30.370064]  slab_reclaimable:34 slab_unreclaimable:4438
>>> [   30.370064]  mapped:0 shmem:0 pagetables:14 bounce:0
>>> [   30.370064]  free:1537719 free_pcp:219 free_cma:0
>>> [   30.370070] Node 0 active_anon:0kB inactive_anon:0kB
>>> active_file:0kB inactive_file:0kB unevictable:0kB isolated(anon):0kB
>>> isolated(file):0kB mapped:0kB dirty:0kB writeback:0kB shmem:0kB
>>> shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 0kB writeback_tmp:0kB
>>> unstable:0kB all_unreclaimable? no
>>> [   30.370073] Node 1 active_anon:0kB inactive_anon:0kB
>>> active_file:0kB inactive_file:0kB unevictable:0kB isolated(anon):0kB
>>> isolated(file):0kB mapped:0kB dirty:0kB writeback:0kB shmem:0kB
>>> shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 0kB writeback_tmp:0kB
>>> unstable:0kB all_unreclaimable? no
>>> [   30.370079] Node 0 DMA free:0kB min:0kB low:0kB high:0kB
>>> reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB
>>> active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB
>>> present:128kB managed:0kB mlocked:0kB kernel_stack:0kB pagetables:0kB
>>> bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
>>> [   30.370084] lowmem_reserve[]: 0 250 6063 6063
>>> [   30.370090] Node 0 DMA32 free:256000kB min:408kB low:664kB
>>> high:920kB reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB
>>> active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB
>>> present:269700kB managed:256000kB mlocked:0kB kernel_stack:0kB
>>> pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
>>> [   30.370094] lowmem_reserve[]: 0 0 5813 5813
>>> [   30.370100] Node 0 Normal free:5894876kB min:9552kB low:15504kB
>>> high:21456kB reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB
>>> active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB
>>> present:8388608kB managed:5953112kB mlocked:0kB kernel_stack:21672kB
>>> pagetables:56kB bounce:0kB free_pcp:876kB local_pcp:176kB free_cma:0kB
>>> [   30.370104] lowmem_reserve[]: 0 0 0 0
>>> [   30.370107] Node 0 DMA: 0*4kB 0*8kB 0*16kB 0*32kB 0*64kB 0*128kB
>>> 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 0kB
>>> [   30.370113] Node 0 DMA32: 0*4kB 0*8kB 0*16kB 0*32kB 0*64kB 0*128kB
>>> 0*256kB 0*512kB 0*1024kB 1*2048kB (M) 62*4096kB (M) = 256000kB
>>> [   30.370119] Node 0 Normal: 2*4kB (M) 3*8kB (ME) 2*16kB (UE) 3*32kB
>>> (UM) 1*64kB (U) 2*128kB (M) 2*256kB (ME) 3*512kB (ME) 3*1024kB (ME)
>>> 3*2048kB (UME) 1436*4096kB (M) = 5893600kB
>>> [   30.370129] Node 0 hugepages_total=0 hugepages_free=0
>>> hugepages_surp=0 hugepages_size=1048576kB
>>> [   30.370130] 0 total pagecache pages
>>> [   30.370132] 0 pages in swap cache
>>> [   30.370134] Swap cache stats: add 0, delete 0, find 0/0
>>> [   30.370135] Free swap  = 0kB
>>> [   30.370136] Total swap = 0kB
>>> [   30.370137] 2164609 pages RAM
>>> [   30.370139] 0 pages HighMem/MovableOnly
>>> [   30.370140] 612331 pages reserved
>>> [   30.370141] 0 pages hwpoisoned
>>> [   30.370143] DMA: failed to allocate 256 KiB pool for atomic
>>> coherent allocation
>> 
>> 
>> During my testing I saw the same error and Chen's  solution corrected it .
> 
> Which combination you are using on your side? I am using Prabhakar's
> suggested environment and can reproduce the issue
> with or without Chen's crashkernel support above 4G patchset.
> 
> I am also using a ThunderX2 platform with latest makedumpfile code and
> kexec-tools (with the suggested patch
> <https://urldefense.com/v3/__https://lists.infradead.org/pipermail/kexec/2020-May/025128.html__;!!GqivPVa7Brio!J6lUig58-Gw6TKZnEEYzEeSU36T-1SqlB1kImU00xtX_lss5Tx-JbUmLE9TJC3foXBLg$ >).
> 
> Thanks,
> Bhupesh


I did this activity 5 months ago and I have moved on to other activities. My DMA failures were related to PCI devices that could not be enumerated because  low-DMA space was not  available  when crashkernel was moved above 4G; I don’t recall the exact platform. 



For this failure , 

>>>  DMA: failed to allocate 256 KiB pool for atomic
>>> coherent allocation


Is due to :


 3618082c
 ("arm64 use both ZONE_DMA and ZONE_DMA32")

With the introduction of ZONE_DMA to support the Raspberry DMA
region below 1G, the crashkernel is placed in the upper 4G
ZONE_DMA_32 region. Since the crashkernel does not have access
to the ZONE_DMA region, it prints out call trace during bootup.

It is due to having this CONFIG item  ON  :


CONFIG_ZONE_DMA=y

Turning off ZONE_DMA fixes a issue and Raspberry PI 4 will
use the device tree to specify memory below 1G.


I would like to see Chen’s feature added , perhaps as EXPERIMENTAL,  so we can get some configuration testing done on it.   It corrects having a DMA zone in low memory while crash-kernel is above 4GB.  This has been going on for a year now. 


Thank you,

John.


( Note  .. I am not on the all the kernel-dlist emails  so this won’t be seen by everyone , -  someone may have to bounce it )

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