Re: [PATCH v8 0/5] support reserving crashkernel above 4G on arm64 kdump

[Prabhakar Kushwaha]

Hi Chen,

On Thu, May 21, 2020 at 3:05 PM Chen Zhou <chenzhou10@xxxxxxxxxx> 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]: http://lists.infradead.org/pipermail/kexec/2020-May/025128.html
> [v1]: https://lkml.org/lkml/2019/4/2/1174
> [v2]: https://lkml.org/lkml/2019/4/9/86
> [v3]: https://lkml.org/lkml/2019/4/9/306
> [v4]: https://lkml.org/lkml/2019/4/15/273
> [v5]: https://lkml.org/lkml/2019/5/6/1360
> [v6]: https://lkml.org/lkml/2019/8/30/142
> [v7]: https://lkml.org/lkml/2019/12/23/411
>
> 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://lists.infradead.org/pipermail/kexec/2020-May/025128.html
Also **without** this patch-set
"https://www.spinics.net/lists/arm-kernel/msg806882.html";

This issue comes whenever crashkernel memory is reserved after 0xc000_0000.
More details discussed earlier in
https://www.spinics.net/lists/arm-kernel/msg806882.html 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

[2]
root@localhost$ dmesg | grep crash
[    0.000000] Reserving 250MB of low memory at 3724MB for crashkernel
(System low RAM: 2029MB)
[    0.000000] crashkernel reserved: 0x0000000e00000000 -
0x0000001000000000 (8192 MB)
[    0.000000] Kernel command line:
BOOT_IMAGE=(hd11,gpt2)/vmlinuz-5.7.0-rc3+
root=UUID=e5c34f86-6727-4668-81f9-f41433555df6 ro crashkernel=250M,low
crashkernel=8G nowatchdog console=ttyAMA0 default_hugepagesz=1G
hugepagesz=1G hugepages=2
[   44.019393]     crashkernel=8G