On 07/21/15 at 03:50pm, Baoquan He wrote: > Hi Dave, > > On 07/21/15 at 03:31pm, Dave Young wrote: > > Hi, Baoquan > > > > The interface was introduced by Yinghai, ccing him. > > > > On 07/19/15 at 10:53pm, Baoquan He wrote: > > > People reported that when allocating crashkernel memory using > > > ",high" and ",low" syntax, there were cases where the reservation > > > of the "high" portion succeeds, but the reservation of the "low" > > > portion fails. Then kexec can load kdump kernel successfully, but > > > the boot of kdump kernel fails as there's no low memory. This is > > > because allocation of low memory for kdump kernel can fail on large > > > systems for reasons. E.g it could be manually specified crashkernel > > > low memory is too large to find in memblock region. > > > > > > In this patch add return value for reserve_crashkernel_low. Then put > > > the crashkernel low memory reserving earlier, just between finding > > > the crashkernel high memory region and reserving crashkernel high > > > memory. Then if crashkernel low memory reserving failed we do not > > > reserve crashkernel high memory but return immediately. Users can > > > take measures when they found kdump kernel cann't be loaded > > > successfully. > > > > So we have 3 sementics now, > > crashkernel ,low > > crashkernel ,high > > crashkernel ,low + crashkernel ,high > > For the last case, we need make sure both ,low and ,high reserved, > > > > Can we assume we need both ,low and ,high being ok if one specify > > these two types in kernel cmdline? > > I think so. the reason why ,low is introduced is swiotlb or pci device > need low memory when crashkernel is reserved above 4G. Low memory is > necessary when ,high is specified unless user can make sure their > machines don't need low memory and specify crashkernel=0,low explictly.
I think forcing user to provide crashkernel=0,low even they do not need is bad, IMHO one should provided crashkernel value they really need.. > > > > > Also in case one suceed, another fail, should we free the reserved memory? > > In this patch it doesn't need to free. Since it just finds an available > memblock region for crashkernel high, then try to reserve crashkernel > low memory. If low memory failed to allocate, it doesn't allocate > crashkernel high memory found, but return immediately. Only if low > memory is allocated successfully, high memory is allocated too > subsequently. Ok, thanks for explanation Dave -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
