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Message-ID: <1359595344.1557.13.camel@kernel>
Date: Wed, 30 Jan 2013 19:22:24 -0600
From: Simon Jeons <simon.jeons@...il.com>
To: Tang Chen <tangchen@...fujitsu.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 Tang,
On Wed, 2013-01-30 at 18:15 +0800, Tang Chen wrote:
> 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].
Sorry, I still confuse. :(
update node_states[N_NORMAL_MEMORY] to node_states[N_MEMORY] or
node_states[N_NORMAL_MEMOR] present 0...ZONE_MOVABLE?
>
> 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.
node_states is what? node_states[N_NORMAL_MEMOR] or
node_states[N_MEMORY]?
>
> 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.
Yup, very clear now. :)
Why check !z1->wait_table in function move_pfn_range_left and function
__add_zone? I think zone->wait_table is initialized in
free_area_init_core, which will be called during system initialization
and hotadd_new_pgdat path.
>
> > 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));
thanks. :)
There is a zone populated check in function online_pages. But zone is
populated in free_area_init_core which will be called during system
initialization and hotadd_new_pgdat path. Why still need this check?
>
> 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.
Please ingore this silly question. :(
>
> 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(-)
> >>
> >> --
> >> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> >> the body to majordomo@...ck.org. For more info on Linux MM,
> >> see: http://www.linux-mm.org/ .
> >> Don't email:<a href=mailto:"dont@...ck.org"> email@...ck.org</a>
> >
> >
> >
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