Messages in this thread | | | Date | Tue, 20 Nov 2012 19:25:13 +0800 | From | Jaegeuk Hanse <> | Subject | Re: [PATCH 0/5] Add movablecore_map boot option. |
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On 11/20/2012 07:07 PM, Yasuaki Ishimatsu wrote: > 2012/11/20 5:53, Andrew Morton wrote: >> On Mon, 19 Nov 2012 22:27:21 +0800 >> Tang Chen <tangchen@cn.fujitsu.com> wrote: >> >>> This patchset provide a boot option for user to specify ZONE_MOVABLE >>> memory >>> map for each node in the system. >>> >>> movablecore_map=nn[KMG]@ss[KMG] >>> >>> This option make sure memory range from ss to ss+nn is movable memory. >>> 1) If the range is involved in a single node, then from ss to the >>> end of >>> the node will be ZONE_MOVABLE. >>> 2) If the range covers two or more nodes, then from ss to the end of >>> the node will be ZONE_MOVABLE, and all the other nodes will only >>> have ZONE_MOVABLE. >>> 3) If no range is in the node, then the node will have no ZONE_MOVABLE >>> unless kernelcore or movablecore is specified. >>> 4) This option could be specified at most MAX_NUMNODES times. >>> 5) If kernelcore or movablecore is also specified, movablecore_map >>> will have >>> higher priority to be satisfied. >>> 6) This option has no conflict with memmap option. >> >> This doesn't describe the problem which the patchset solves. I can >> kinda see where it's coming from, but it would be nice to have it all >> spelled out, please. >> > >> - What is wrong with the kernel as it stands? > > If we hot remove a memroy, the memory cannot have kernel memory, > because Linux cannot migrate kernel memory currently. Therefore, > we have to guarantee that the hot removed memory has only movable > memoroy. > > Linux has two boot options, kernelcore= and movablecore=, for > creating movable memory. These boot options can specify the amount > of memory use as kernel or movable memory. Using them, we can > create ZONE_MOVABLE which has only movable memory. > > But it does not fulfill a requirement of memory hot remove, because > even if we specify the boot options, movable memory is distributed > in each node evenly. So when we want to hot remove memory which > memory range is 0x80000000-0c0000000, we have no way to specify > the memory as movable memory.
Could you explain why can't specify the memory as movable memory in this case?
> > So we proposed a new feature which specifies memory range to use as > movable memory. > >> - What are the possible ways of solving this? > > I thought 2 ways to specify movable memory. > 1. use firmware information > 2. use boot option > > 1. use firmware information > According to ACPI spec 5.0, SRAT table has memory affinity structure > and the structure has Hot Pluggable Filed. See "5.2.16.2 Memory > Affinity Structure". If we use the information, we might be able to > specify movable memory by firmware. For example, if Hot Pluggable > Filed is enabled, Linux sets the memory as movable memory. > > 2. use boot option > This is our proposal. New boot option can specify memory range to use > as movable memory. > >> - Describe the chosen way, explain why it is superior to alternatives > > We chose second way, because if we use first way, users cannot change > memory range to use as movable memory easily. We think if we create > movable memory, performance regression may occur by NUMA. In this case,
Could you explain why regression occur in details?
> user can turn off the feature easily if we prepare the boot option. > And if we prepare the boot optino, the user can select which memory > to use as movable memory easily. > > Thanks, > Yasuaki Ishimatsu > >> >> The amount of manual system configuration in this proposal looks quite >> high. Adding kernel boot parameters really is a last resort. Why was >> it unavoidable here? >> > > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
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