On 09/04/20 at 11:04am, Dave Young wrote: > On 09/03/20 at 07:26pm, chenzhou wrote: > > 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? > > Hmm, took another look at the option CONFIG_PHYSICAL_ALIGN > config PHYSICAL_ALIGN > hex "Alignment value to which kernel should be aligned" > default "0x200000" > range 0x2000 0x1000000 if X86_32 > range 0x200000 0x1000000 if X86_64 > > According to above, I think the 16M should come from the largest value > But the default value is 2M, with smaller value reservation can have > more chance to succeed. > > It seems we still need arch specific CRASH_ALIGN, but the initial > version you added the #ifdef for different arches, can you move the > macro to arch specific headers?
And just keep the x86 align value as is, I can try to change the x86 value later to CONFIG_PHYSICAL_ALIGN, in this way this series can be cleaner. > > Thanks > Dave _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec