On Thu, May 05, 2022 at 11:00:19AM +0800, Baoquan He wrote: > On 05/03/22 at 11:00pm, Catalin Marinas wrote: > > So, to recap, IIUC you are fine with: > > > > crashkernel=Y - allocate within ZONE_DMA with fallback > > above with a default in ZONE_DMA (like > > x86, 256M or swiotlb size) > > Ack to this one. > > > > crashkernel=Y,high - allocate from above ZONE_DMA > > Not exactly. If there's only ZONE_DMA, crashkernel,high will > be reserved in ZONE_DMA, and crashkernel,low will be ignored. > Other than this, ack. Yes, that's fine. > > crashkernel=Y,low - allocate within ZONE_DMA > > Ack to this one. > > > > 'crashkernel' overrides the high and low while the latter two can be > > passed independently. > > crashkernel=,high can be passed independently, then a crashkernel=,low > is needed implicitly. If people don't want crashkernel=,low > explicitly, crashkernel=0,low need be specified. I find this complicating the interface. I don't know the background to the x86 implementation but we diverge already on arm64 since we talk about ZONE_DMA rather than 4G limit (though for most platforms these would be the same). I guess we could restate the difference between crashkernel= and crashkernel=,high as the hint to go for allocation above ZONE_DMA first. > An independent crashkernel=,low makes no sense. Crashkernel=,low > should be paird with crashkernel=,high. You could argue that crashkernel=,low gives the current crashkernel= behaviour, i.e. either all within ZONE_DMA or fail to allocate. So it may have some value on its own. > My personal opinion according to the existed senmantics on x86. > Otherwise, the guidance of crashkernel= |,high|,low reservation > will be complicated to write. It's more that I find the current semantics unnecessarily confusing. But even reading the x86_64 text it's not that clear. For example the default low allocation for crashkernel= and crashkernel=,high is only mentioned in the crashkernel=,low description. -- Catalin
