Subject: Re: [PATCH v6 00/15] memory-hotplug: hot-remove physical memory

From: Simon Jeons <[email-masked]>
Date: Tue, 29 Jan 2013 06:52:53 -0600

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.

* 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. In function move_pfn_range_left, why end <= z2->zone_start_pfn is not
correct? The comments said that must include/overlap, why?

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?

4. Could you summarize the difference implementation between hot-add and
logic-add, hot-remove and logic-remove?   

> 
> 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 <[email-masked]> 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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