Messages in this thread | | | Subject | Re: [PATCH v11 3/5] arm64: kdump: reimplement crashkernel=X | From | chenzhou <> | Date | Thu, 3 Sep 2020 19:26:27 +0800 |
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Hi Catalin,
On 2020/9/3 1:09, Catalin Marinas wrote: > On Sat, Aug 01, 2020 at 09:08:54PM +0800, Chen Zhou wrote: >> 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. If reserving crashkernel above 4G, in this case, crash dump >> kernel will boot failure because there is no low memory available >> for allocation. >> 3. Since commit 1a8e1cef7603 ("arm64: use both ZONE_DMA and ZONE_DMA32"), >> if the memory reserved for crash dump kernel falled in ZONE_DMA32, >> the devices in crash dump kernel need to use ZONE_DMA will alloc >> fail. >> >> To solve these issues, change the behavior of crashkernel=X. >> crashkernel=X tries low allocation in ZONE_DMA, and fall back to >> high allocation if it fails. >> >> If requized size X is too large and leads to very little free memory >> in ZONE_DMA after low allocation, the system may not work normally. >> So add a threshold and go for high allocation directly if the required >> size is too large. The value of threshold is set as the half of >> the low memory. >> >> If crash_base is outside ZONE_DMA, try to allocate at least 256M in >> ZONE_DMA automatically. "crashkernel=Y,low" can be used to allocate >> specified size low memory. > Except for the threshold to keep zone ZONE_DMA memory, > reserve_crashkernel() looks very close to the x86 version. Shall we try > to make this generic as well? In the first instance, you could avoid the > threshold check if it takes an explicit ",high" option. Ok, i will try to do this.
I look into the function reserve_crashkernel() of x86 and found the start address is CRASH_ALIGN in function memblock_find_in_range(), which is different with arm64.
I don't figure out why is CRASH_ALIGN in x86, is there any specific reason?
Thanks, Chen Zhou
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