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Message-ID: <5108F2B3.3090506@cn.fujitsu.com>
Date: Wed, 30 Jan 2013 18:15:15 +0800
From: Tang Chen <tangchen@...fujitsu.com>
To: Simon Jeons <simon.jeons@...il.com>
CC: akpm@...ux-foundation.org, rientjes@...gle.com,
len.brown@...el.com, benh@...nel.crashing.org, paulus@...ba.org,
cl@...ux.com, minchan.kim@...il.com,
kosaki.motohiro@...fujitsu.com, isimatu.yasuaki@...fujitsu.com,
wujianguo@...wei.com, wency@...fujitsu.com, hpa@...or.com,
linfeng@...fujitsu.com, laijs@...fujitsu.com, mgorman@...e.de,
yinghai@...nel.org, glommer@...allels.com, x86@...nel.org,
linux-mm@...ck.org, linux-kernel@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
linux-ia64@...r.kernel.org, cmetcalf@...era.com,
sparclinux@...r.kernel.org
Subject: Re: [PATCH v6 00/15] memory-hotplug: hot-remove physical memory
Hi Simon,
Please see below. :)
On 01/29/2013 08:52 PM, Simon Jeons wrote:
> Hi Tang,
>
> On Wed, 2013-01-09 at 17:32 +0800, Tang Chen wrote:
>> Here is the physical memory hot-remove patch-set based on 3.8rc-2.
>
> Some questions ask you, not has relationship with this patchset, but is
> memory hotplug stuff.
>
> 1. In function node_states_check_changes_online:
>
> comments:
> * If we don't have HIGHMEM nor movable node,
> * node_states[N_NORMAL_MEMORY] contains nodes which have zones of
> * 0...ZONE_MOVABLE, set zone_last to ZONE_MOVABLE.
>
> How to understand it? Why we don't have HIGHMEM nor movable node and
> node_staes[N_NORMAL_MEMORY] contains 0...ZONE_MOVABLE, IIUC,
> N_NORMAL_MEMORY only means the node has regular memory.
>
First of all, I think we need to understand why we need N_MEMORY.
In order to support movable node, which has only ZONE_MOVABLE (the last
zone),
we introduce N_MEMORY to represent the node has normal, highmem and
movable memory.
Here, "we have movable node" means you configured CONFIG_MOVABLE_NODE.
This config option doesn't mean we don't have movable pages, (NO)
it means we don't have a node which has only movable pages (only have
ZONE_MOVABLE). (YES)
Here, if we don't have CONFIG_MOVABLE_NODE (we don't have movable node),
we don't need a
separate node_states[] element to represent a particular node because we
won't have a node
which has only ZONE_MOVABLE.
So,
1) if we don't have highmem nor movable node, N_MEMORY == N_HIGH_MEMORY
== N_NORMAL_MEMORY,
which means N_NORMAL_MEMORY effects as N_MEMORY. If we online pages
as movable, we need
to update node_states[N_NORMAL_MEMORY].
Please refer to the definition of enum zone_type, if we don't have
CONFIG_HIGHMEM, we won't
have ZONE_HIGHMEM, but ZONE_NORMAL and ZONE_MOVABLE will always there.
So we can have movable
pages, and the zone_last should be ZONE_MOVABLE.
Again, because we won't have a node only having ZONE_MOVABLE, so we just
need to update
node_states[N_NORMAL_MEMORY].
> * If we don't have movable node, node_states[N_NORMAL_MEMORY]
> * contains nodes which have zones of 0...ZONE_MOVABLE,
> * set zone_last to ZONE_MOVABLE.
>
> How to understand?
2) this code is in #ifdef CONFIG_HIGHMEM, which means we have highmem,
so if we don't have
movable node, N_MEMORY == N_HIGH_MEMORY, and N_HIGH_MEMORY effects
as N_MEMORY. If we
online pages as movable, we need to update node_states[N_NORMAL_MEMORY].
>
> 2. In function move_pfn_range_left, why end<= z2->zone_start_pfn is not
> correct? The comments said that must include/overlap, why?
>
This one is easy, if I understand you correctly.
move_pfn_range_left() is used to move the left most part [start_pfn,
end_pfn) of z2 to z1.
So if end_pfn<= z2->zone_start_pfn, it means [start_pfn, end_pfn) is not
part of z2.
Then it fails.
> 3. In function online_pages, the normal case(w/o online_kenrel,
> online_movable), why not check if the new zone is overlap with adjacent
> zones?
>
Can a zone overlap with the others ? I don't think so.
One pfn could only be in one zone,
zone = page_zone(pfn_to_page(pfn));
it could overlap with others, I think. :)
But maybe I misunderstand you. :)
> 4. Could you summarize the difference implementation between hot-add and
> logic-add, hot-remove and logic-remove?
Sorry, I don't quite understand what do you mean by logic-add/remove.
Would you please explain more ?
If you meant the sys fs interfaces, I think they are just another set of
entrances
of memory hotplug.
Thanks. :)
>
>
>>
>> This patch-set aims to implement physical memory hot-removing.
>>
>> The patches can free/remove the following things:
>>
>> - /sys/firmware/memmap/X/{end, start, type} : [PATCH 4/15]
>> - memmap of sparse-vmemmap : [PATCH 6,7,8,10/15]
>> - page table of removed memory : [RFC PATCH 7,8,10/15]
>> - node and related sysfs files : [RFC PATCH 13-15/15]
>>
>>
>> Existing problem:
>> If CONFIG_MEMCG is selected, we will allocate memory to store page cgroup
>> when we online pages.
>>
>> For example: there is a memory device on node 1. The address range
>> is [1G, 1.5G). You will find 4 new directories memory8, memory9, memory10,
>> and memory11 under the directory /sys/devices/system/memory/.
>>
>> If CONFIG_MEMCG is selected, when we online memory8, the memory stored page
>> cgroup is not provided by this memory device. But when we online memory9, the
>> memory stored page cgroup may be provided by memory8. So we can't offline
>> memory8 now. We should offline the memory in the reversed order.
>>
>> When the memory device is hotremoved, we will auto offline memory provided
>> by this memory device. But we don't know which memory is onlined first, so
>> offlining memory may fail.
>>
>> In patch1, we provide a solution which is not good enough:
>> Iterate twice to offline the memory.
>> 1st iterate: offline every non primary memory block.
>> 2nd iterate: offline primary (i.e. first added) memory block.
>>
>> And a new idea from Wen Congyang<wency@...fujitsu.com> is:
>> allocate the memory from the memory block they are describing.
>>
>> But we are not sure if it is OK to do so because there is not existing API
>> to do so, and we need to move page_cgroup memory allocation from MEM_GOING_ONLINE
>> to MEM_ONLINE. And also, it may interfere the hugepage.
>>
>>
>>
>> How to test this patchset?
>> 1. apply this patchset and build the kernel. MEMORY_HOTPLUG, MEMORY_HOTREMOVE,
>> ACPI_HOTPLUG_MEMORY must be selected.
>> 2. load the module acpi_memhotplug
>> 3. hotplug the memory device(it depends on your hardware)
>> You will see the memory device under the directory /sys/bus/acpi/devices/.
>> Its name is PNP0C80:XX.
>> 4. online/offline pages provided by this memory device
>> You can write online/offline to /sys/devices/system/memory/memoryX/state to
>> online/offline pages provided by this memory device
>> 5. hotremove the memory device
>> You can hotremove the memory device by the hardware, or writing 1 to
>> /sys/bus/acpi/devices/PNP0C80:XX/eject.
>
> Is there a similar knode to hot-add the memory device?
>
>>
>>
>> Note: if the memory provided by the memory device is used by the kernel, it
>> can't be offlined. It is not a bug.
>>
>>
>> Changelogs from v5 to v6:
>> Patch3: Add some more comments to explain memory hot-remove.
>> Patch4: Remove bootmem member in struct firmware_map_entry.
>> Patch6: Repeatedly register bootmem pages when using hugepage.
>> Patch8: Repeatedly free bootmem pages when using hugepage.
>> Patch14: Don't free pgdat when offlining a node, just reset it to 0.
>> Patch15: New patch, pgdat is not freed in patch14, so don't allocate a new
>> one when online a node.
>>
>> Changelogs from v4 to v5:
>> Patch7: new patch, move pgdat_resize_lock into sparse_remove_one_section() to
>> avoid disabling irq because we need flush tlb when free pagetables.
>> Patch8: new patch, pick up some common APIs that are used to free direct mapping
>> and vmemmap pagetables.
>> Patch9: free direct mapping pagetables on x86_64 arch.
>> Patch10: free vmemmap pagetables.
>> Patch11: since freeing memmap with vmemmap has been implemented, the config
>> macro CONFIG_SPARSEMEM_VMEMMAP when defining __remove_section() is
>> no longer needed.
>> Patch13: no need to modify acpi_memory_disable_device() since it was removed,
>> and add nid parameter when calling remove_memory().
>>
>> Changelogs from v3 to v4:
>> Patch7: remove unused codes.
>> Patch8: fix nr_pages that is passed to free_map_bootmem()
>>
>> Changelogs from v2 to v3:
>> Patch9: call sync_global_pgds() if pgd is changed
>> Patch10: fix a problem int the patch
>>
>> Changelogs from v1 to v2:
>> Patch1: new patch, offline memory twice. 1st iterate: offline every non primary
>> memory block. 2nd iterate: offline primary (i.e. first added) memory
>> block.
>>
>> Patch3: new patch, no logical change, just remove reduntant codes.
>>
>> Patch9: merge the patch from wujianguo into this patch. flush tlb on all cpu
>> after the pagetable is changed.
>>
>> Patch12: new patch, free node_data when a node is offlined.
>>
>>
>> Tang Chen (6):
>> memory-hotplug: move pgdat_resize_lock into
>> sparse_remove_one_section()
>> memory-hotplug: remove page table of x86_64 architecture
>> memory-hotplug: remove memmap of sparse-vmemmap
>> memory-hotplug: Integrated __remove_section() of
>> CONFIG_SPARSEMEM_VMEMMAP.
>> memory-hotplug: remove sysfs file of node
>> memory-hotplug: Do not allocate pdgat if it was not freed when
>> offline.
>>
>> Wen Congyang (5):
>> memory-hotplug: try to offline the memory twice to avoid dependence
>> memory-hotplug: remove redundant codes
>> memory-hotplug: introduce new function arch_remove_memory() for
>> removing page table depends on architecture
>> memory-hotplug: Common APIs to support page tables hot-remove
>> memory-hotplug: free node_data when a node is offlined
>>
>> Yasuaki Ishimatsu (4):
>> memory-hotplug: check whether all memory blocks are offlined or not
>> when removing memory
>> memory-hotplug: remove /sys/firmware/memmap/X sysfs
>> memory-hotplug: implement register_page_bootmem_info_section of
>> sparse-vmemmap
>> memory-hotplug: memory_hotplug: clear zone when removing the memory
>>
>> arch/arm64/mm/mmu.c | 3 +
>> arch/ia64/mm/discontig.c | 10 +
>> arch/ia64/mm/init.c | 18 ++
>> arch/powerpc/mm/init_64.c | 10 +
>> arch/powerpc/mm/mem.c | 12 +
>> arch/s390/mm/init.c | 12 +
>> arch/s390/mm/vmem.c | 10 +
>> arch/sh/mm/init.c | 17 ++
>> arch/sparc/mm/init_64.c | 10 +
>> arch/tile/mm/init.c | 8 +
>> arch/x86/include/asm/pgtable_types.h | 1 +
>> arch/x86/mm/init_32.c | 12 +
>> arch/x86/mm/init_64.c | 390 +++++++++++++++++++++++++++++
>> arch/x86/mm/pageattr.c | 47 ++--
>> drivers/acpi/acpi_memhotplug.c | 8 +-
>> drivers/base/memory.c | 6 +
>> drivers/firmware/memmap.c | 96 +++++++-
>> include/linux/bootmem.h | 1 +
>> include/linux/firmware-map.h | 6 +
>> include/linux/memory_hotplug.h | 15 +-
>> include/linux/mm.h | 4 +-
>> mm/memory_hotplug.c | 459 +++++++++++++++++++++++++++++++---
>> mm/sparse.c | 8 +-
>> 23 files changed, 1094 insertions(+), 69 deletions(-)
>>
>> --
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>
>
>
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