> On Jan 16, 2020, at 9:17 AM, James Morse <james.morse@xxxxxxx> wrote: > > Hi guys, > > On 28/12/2019 09:32, Dave Young wrote: >> On 12/27/19 at 07:04pm, Chen Zhou wrote: >>> On 2019/12/27 13:54, Dave Young wrote: >>>> On 12/23/19 at 11:23pm, Chen Zhou wrote: >>>>> In preparation for supporting reserve_crashkernel_low in arm64 as >>>>> x86_64 does, move reserve_crashkernel_low() into kernel/crash_core.c. >>>>> >>>>> Note, in arm64, we reserve low memory if and only if crashkernel=X,low >>>>> is specified. Different with x86_64, don't set low memory automatically. >>>> >>>> Do you have any reason for the difference? I'd expect we have same >>>> logic if possible and remove some of the ifdefs. >>> >>> In x86_64, if we reserve crashkernel above 4G, then we call reserve_crashkernel_low() >>> to reserve low memory. >>> >>> In arm64, to simplify, we call reserve_crashkernel_low() at the beginning of reserve_crashkernel() >>> and then relax the arm64_dma32_phys_limit if reserve_crashkernel_low() allocated something. >>> In this case, if reserve crashkernel below 4G there will be 256M low memory set automatically >>> and this needs extra considerations. > >> Sorry that I did not read the old thread details and thought that is >> arch dependent. But rethink about that, it would be better that we can >> have same semantic about crashkernel parameters across arches. If we >> make them different then it causes confusion, especially for >> distributions. > > Surely distros also want one crashkernel* string they can use on all platforms without > having to detect the kernel version, platform or changeable memory layout... > > >> OTOH, I thought if we reserve high memory then the low memory should be >> needed. There might be some exceptions, but I do not know the exact >> one, > >> can we make the behavior same, and special case those systems which >> do not need low memory reservation. > > Its tricky to work out which systems are the 'normal' ones. > > We don't have a fixed memory layout for arm64. Some systems have no memory below 4G. > Others have no memory above 4G. > > Chen Zhou's machine has some memory below 4G, but its too precious to reserve a large > chunk for kdump. Without any memory below 4G some of the drivers won't work. > > I don't see what distros can set as their default for all platforms if high/low are > mutually exclusive with the 'crashkernel=' in use today. How did x86 navigate this, ... or > was it so long ago? > > No one else has reported a problem with the existing placement logic, hence treating this > 'low' thing as the 'in addition' special case. Hi, I am seeing similar Arm crash dump issues on 5.4 kernels where we need rather large amount of crashkernel memory reserved that is not available below 4GB ( The maximum reserved size appears to be around 768M ) . When I pick memory range higher than 4GB , I see adapters that fail to initialize : There is no low-memory <4G memory for DMA ; [ 11.506792] kworker/0:14: page allocation failure: order:0, mode:0x104(GFP_DMA32|__GFP_ZERO), nodemask=(null),cpuset=/,mems_allowed=0 [ 11.518793] CPU: 0 PID: 150 Comm: kworker/0:14 Not tainted 5.4.0-1948.3.el8uek.aarch64 #1 [ 11.526955] Hardware name: To be filled by O.E.M. Saber/Saber, BIOS 0ACKL025 01/18/2019 [ 11.534948] Workqueue: events work_for_cpu_fn [ 11.539291] Call trace: [ 11.541727] dump_backtrace+0x0/0x18c [ 11.545376] show_stack+0x24/0x30 [ 11.548679] dump_stack+0xbc/0xe0 [ 11.551982] warn_alloc+0xf0/0x15c [ 11.555370] __alloc_pages_slowpath+0xb4c/0xb84 [ 11.559887] __alloc_pages_nodemask+0x2d0/0x330 [ 11.564405] alloc_pages_current+0x8c/0xf8 [ 11.568496] ttm_bo_device_init+0x188/0x220 [ttm] [ 11.573187] drm_vram_mm_init+0x58/0x80 [drm_vram_helper] [ 11.578572] drm_vram_helper_alloc_mm+0x64/0xb0 [drm_vram_helper] [ 11.584655] ast_mm_init+0x38/0x80 [ast] [ 11.588566] ast_driver_load+0x474/0xa70 [ast] [ 11.593029] drm_dev_register+0x144/0x1c8 [drm] [ 11.597573] drm_get_pci_dev+0xa4/0x168 [drm] [ 11.601919] ast_pci_probe+0x8c/0x9c [ast] [ 11.606004] local_pci_probe+0x44/0x98 [ 11.609739] work_for_cpu_fn+0x20/0x30 [ 11.613474] process_one_work+0x1c4/0x41c [ 11.617470] worker_thread+0x150/0x4b0 [ 11.621206] kthread+0x110/0x114 [ 11.624422] ret_from_fork+0x10/0x18 This failure is related to a graphics adapter. The more complex kdump configurations that use networking stack to NFS mount a filesystem to dump to , or use ssh to copy to another machine, require more crashkernel memory reservations than perhaps the “default*” settings of a minimal kdump that creates a minimal vmcore to local storage in /var/crash. If crashkernel is too small I get Out of Memory issues and the entire vmcore process fails. ( *default kdump setting I assume are a minimal vmcore to /var/crash using primary boot device where /root is located ) > > >>> previous discusses: >>> https://urldefense.proofpoint.com/v2/url?u=https-3A__lkml.org_lkml_2019_6_5_670&d=DwICAg&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=t2fPg9D87F7D8jm0_3CG9yoiIKdRg4qc_thBw4bzMhc&m=jOAu1DTDpohsWszalfTCYx46eGF19TSWVLchN5yBPgk&s=gS9BLOkmj78lP5L7SP6_VLHwvP249uWKaE2R7N7sxgM&e= >>> https://urldefense.proofpoint.com/v2/url?u=https-3A__lkml.org_lkml_2019_6_13_229&d=DwICAg&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=t2fPg9D87F7D8jm0_3CG9yoiIKdRg4qc_thBw4bzMhc&m=jOAu1DTDpohsWszalfTCYx46eGF19TSWVLchN5yBPgk&s=U1Nis29n3A7XSBzED53fiE4MDAv5NlxYp1UorvvBOOw&e= >> >> Another concern from James: >> " >> With both crashk_low_res and crashk_res, we end up with two entries in /proc/iomem called >> "Crash kernel". Because its sorted by address, and kexec-tools stops searching when it >> find "Crash kernel", you are always going to get the kernel placed in the lower portion. >> " >> >> The kexec-tools code is iterating all "Crash kernel" ranges and add them >> in an array. In X86 code, it uses the higher range to locate memory. > > Then my hurried reading of what the user-space code does was wrong! > > If kexec-tools places the kernel in the low region, there may not be enough memory left > for whatever purpose it was reserved for. This was the motivation for giving it a > different name. > > > Thanks, > > James > > _______________________________________________ > kexec mailing list > kexec@xxxxxxxxxxxxxxxxxxx > https://urldefense.proofpoint.com/v2/url?u=http-3A__lists.infradead.org_mailman_listinfo_kexec&d=DwICAg&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=t2fPg9D87F7D8jm0_3CG9yoiIKdRg4qc_thBw4bzMhc&m=jOAu1DTDpohsWszalfTCYx46eGF19TSWVLchN5yBPgk&s=bqp02iQDP_Ez-XvLIvj-IPHqbbZwMPlDgmEcG8vhXFE&e=
