On Saturday, 14 July 2007 07:48, Huang, Ying wrote: > On Fri, 2007-07-13 at 10:43 -0600, Eric W. Biederman wrote: > > > Why a assembly stub is necessary? Is it not sufficient that just > > > continue to complete a normal boot (hot add the reset of memory) or load > > > the hibernated kernel (hibernated image) and jump to it? > > > > I was thinking the assembly stub would be the small piece that jumps > > to loaded hibernated kernel. Quite possibly we could just get away > > with providing no memory and just an entry point to kexec but it > > makes sense to me to plan on running a couple of instructions. > > Oh, I got it. In my patch, there is such assembly stub in > arch/i386/kernel/kexec_jump.S. I think it is needed to restore basic CPU > state and accommodate some position independent restore code (such as > memory restore code). > > > Actually the way the kexec infrastructure it might be reasonable to > > just use sys_kexec_load to load the entire hibernated image. Except > > for the fact that sys_kexec_load requires the source pages to be > > in the processes memory image the code shouldn't have the 50% of > > memory limitation already. > > > > If we can get that going we don't even need to restrict the first > > kernels memory. So it might just require teaching sys_kexec_load > > how to steal process pages. Anyway something to think about. > > As for memory backupping and restoring during hibernating and resuming, > I think a possible picture can be as follow: > > Memory: > > Total memory: 512M > Memory used by hibernating/resuming kernel: 0~16M > > > Hibernating process: > > 1. Normal kernel running > 2. Hibernating is triggered, sys_kexec_load is used to load > hibernating kernel and initramfs into memory. Then > sys_reboot(LINUX_REBOOT_CMD_KSPAWN) is invoked. > 3. In sys_reboot, kexec_jump is called to save device/CPU state, > then relocate_kernel is called. kexec_jump and relocate_kernel > reside in individual page in 16M~512M. OK What's going to happen to devices at this point? > 4. In relocate_kernel, 0~16M is backupped firstly, then the > hibernating kernel and initramfs is copied to 0~16M, after that, > the hibernating kernel is booted. > 5. In hibernating kernel, the memory of normal kernel (it is in > 16M~512M) is saved into a hibernation image through /dev/mem > and ELF header. I don't think it can be _that_ simple: (a) what about processes' memory (b) what about areas that shouldn't be saved? > Resume process: > > 1. Resuming kernel is booted as a normal kernel, but the memory is > restricted to 0~16M. > 2. Checking whether there is a effective hibernation image. If > there isn't, the memory of 16M~512M is hot added, and the normal > boot up process continues; If there is, a resuming process is > triggered. > 3. sys_kexec_load is used to restore the memory state of hibernated > kernel. The sys_kexec_load works in crashdump way, that is, the > hibernation image is copied to destination location in 16M~512M > in sys_kexec_load instead of relocate_kernel. There is no half > of memory size restriction. > 4. sys_reboot is called to trigger jumping back, which will jump back > to kexec_jump of hibernated kernel. > 5. In kexec_jump of hibernated kernel, the memory of 0~16M is copied > back from the backup area in 16M~512M. The memory state of > hibernated kernel is restored totally. The CPU and device state > can be restored after that. Well, I don't know why this needs to be that complicated. We already have code in the mainline that's able to load a large hibernation image into memory and jump to the kernel being restored. And it has _no_ 50% of RAM limitation, this is the _saving_ part of the current code that this limitation comes from. Greetings, Rafael -- "Premature optimization is the root of all evil." - Donald Knuth _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
