Re: [PATCH -v4 0/14] mm: make movable onlining suck less

[Wei Yang <richard.weiyang@gmail.com>]

Hi, Michal

I am not that familiar with hotplug and trying to catch up the issue
 and your solution.

One potential issue I found is we don't check the physical boundary
when add_memory_resource().

For example, on x86-64, only 64T physical memory is supported currently.
Looks it is expanded after 5-level pagetable is introduced. While there is
still some limitations on this. But we don't check the boundary I think.

During the bootup, this is ensured by the max_pfn which is guaranteed to
be under MAX_ARCH_PFN. I don't see some limitation on this when doing
 hotplug.

Here is my very simple check on this, while it seems not every arch has
 MAX_ARCH_PFN. Willing to hear from you.

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 6fa7208bcd56..27541566f9ac 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1355,7 +1355,12 @@ int __ref add_memory_resource(int nid, struct
resource *res, bool online)
        int ret;

        start = res->start;
+       if (start > (MAX_ARCH_PFN << PAGE_SHIFT))
+               return -EINVAL;
+
        size = resource_size(res);
+       if ((start + size) > (MAX_ARCH_PFN << PAGE_SHIFT))
+               size = (MAX_ARCH_PFN << PAGE_SHIFT) - start;

        ret = check_hotplug_memory_range(start, size);
        if (ret)

On Mon, May 15, 2017 at 4:58 PM, Michal Hocko <mhocko@kernel.org> wrote:
> Hi,
> The last version of this series has been posted here [1]. The timing wasn't
> all that great so this is mostly a resubmit. I've added one additional patch
> to fix another pfn walker noticed by Joonsoo (this is patch 11) and also
> added a clarification for pfn_valid() and offline pages.
>
> There is still a lot of work on top - namely this implementation doesn't
> support reonlining to a different zone on the zones boundaries but I
> will do that in a separate series because this one is getting quite
> large already and it should work reasonably well now.
>
> Joonsoo had some worries about pfn_valid and suggested to change its
> semantic to return false on offline holes but I would be rally worried
> to change a established semantic used by a lot of code and so I have
> introuduced pfn_to_online_page helper instead. If this is seen as a
> controversial point I would rather drop pfn_to_online_page and related
> patches as they are not stictly necessary because the code would be
> similarly broken as now wrt. offline holes.
>
> This is a rebase on top of the current mmotm tree (mmotm-2017-05-12-15-53)
> and the full series is in
> git://git.kernel.org/pub/scm/linux/kernel/git/mhocko/mm.git try
> attempts/rewrite-mem_hotplug branch.
>
> Motivation:
> Movable onlining is a real hack with many downsides - mainly
> reintroduction of lowmem/highmem issues we used to have on 32b systems -
> but it is the only way to make the memory hotremove more reliable which
> is something that people are asking for.
>
> The current semantic of memory movable onlinening is really cumbersome,
> however. The main reason for this is that the udev driven approach is
> basically unusable because udev races with the memory probing while only
> the last memory block or the one adjacent to the existing zone_movable
> are allowed to be onlined movable. In short the criterion for the
> successful online_movable changes under udev's feet. A reliable udev
> approach would require a 2 phase approach where the first successful
> movable online would have to check all the previous blocks and online
> them in descending order. This is hard to be considered sane.
>
> This patchset aims at making the onlining semantic more usable. First of
> all it allows to online memory movable as long as it doesn't clash with
> the existing ZONE_NORMAL. That means that ZONE_NORMAL and ZONE_MOVABLE
> cannot overlap. Currently I preserve the original ordering semantic so
> the zone always precedes the movable zone but I have plans to remove this
> restriction in future because it is not really necessary.
>
> First 3 patches are cleanups which should be ready to be merged right
> away (unless I have missed something subtle of course).
>
> Patch 4 deals with ZONE_DEVICE dependencies down the __add_pages path.
>
> Patch 5 deals with implicit assumptions of register_one_node on pgdat
> initialization.
>
> Patches 6-10 deal with offline holes in the zone for pfn walkers. I
> hope I got all of them right but people familiar with compaction should
> double check this.
>
> Patch 11 is the core of the change. In order to make it easier to review
> I have tried it to be as minimalistic as possible and the large code
> removal is moved to patch 14.
>
> Patch 12 is a trivial follow up cleanup. Patch 13 fixes sparse warnings
> and finally patch 14 removes the unused code.
>
> I have tested the patches in kvm:
> # qemu-system-x86_64 -enable-kvm -monitor pty -m 2G,slots=4,maxmem=4G -numa node,mem=1G -numa node,mem=1G ...
>
> and then probed the additional memory by
> (qemu) object_add memory-backend-ram,id=mem1,size=1G
> (qemu) device_add pc-dimm,id=dimm1,memdev=mem1
>
> Then I have used this simple script to probe the memory block by hand
> # cat probe_memblock.sh
> #!/bin/sh
>
> BLOCK_NR=$1
>
> # echo $((0x100000000+$BLOCK_NR*(128<<20))) > /sys/devices/system/memory/probe
>
> # for i in $(seq 10); do sh probe_memblock.sh $i; done
> # grep . /sys/devices/system/memory/memory3?/valid_zones 2>/dev/null
> /sys/devices/system/memory/memory33/valid_zones:Normal Movable
> /sys/devices/system/memory/memory34/valid_zones:Normal Movable
> /sys/devices/system/memory/memory35/valid_zones:Normal Movable
> /sys/devices/system/memory/memory36/valid_zones:Normal Movable
> /sys/devices/system/memory/memory37/valid_zones:Normal Movable
> /sys/devices/system/memory/memory38/valid_zones:Normal Movable
> /sys/devices/system/memory/memory39/valid_zones:Normal Movable
>
> The main difference to the original implementation is that all new
> memblocks can be both online_kernel and online_movable initially
> because there is no clash obviously. For the comparison the original
> implementation would have
>
> /sys/devices/system/memory/memory33/valid_zones:Normal
> /sys/devices/system/memory/memory34/valid_zones:Normal
> /sys/devices/system/memory/memory35/valid_zones:Normal
> /sys/devices/system/memory/memory36/valid_zones:Normal
> /sys/devices/system/memory/memory37/valid_zones:Normal
> /sys/devices/system/memory/memory38/valid_zones:Normal
> /sys/devices/system/memory/memory39/valid_zones:Normal Movable
>
> Now
> # echo online_movable > /sys/devices/system/memory/memory34/state
> # grep . /sys/devices/system/memory/memory3?/valid_zones 2>/dev/null
> /sys/devices/system/memory/memory33/valid_zones:Normal Movable
> /sys/devices/system/memory/memory34/valid_zones:Movable
> /sys/devices/system/memory/memory35/valid_zones:Movable
> /sys/devices/system/memory/memory36/valid_zones:Movable
> /sys/devices/system/memory/memory37/valid_zones:Movable
> /sys/devices/system/memory/memory38/valid_zones:Movable
> /sys/devices/system/memory/memory39/valid_zones:Movable
>
> Block 33 can still be online both kernel and movable while all
> the remaining can be only movable.
> /proc/zonelist says
> Node 0, zone   Normal
>   pages free     0
>         min      0
>         low      0
>         high     0
>         spanned  0
>         present  0
> --
> Node 0, zone  Movable
>   pages free     32753
>         min      85
>         low      117
>         high     149
>         spanned  32768
>         present  32768
>
> A new memblock at a lower address will result in a new memblock (32)
> which will still allow both Normal and Movable.
> # sh probe_memblock.sh 0
> # grep . /sys/devices/system/memory/memory3[2-5]/valid_zones 2>/dev/null
> /sys/devices/system/memory/memory32/valid_zones:Normal Movable
> /sys/devices/system/memory/memory33/valid_zones:Normal Movable
> /sys/devices/system/memory/memory34/valid_zones:Movable
> /sys/devices/system/memory/memory35/valid_zones:Movable
>
> and online_kernel will convert it to the zone normal properly
> while 33 can be still onlined both ways.
> # echo online_kernel > /sys/devices/system/memory/memory32/state
> # grep . /sys/devices/system/memory/memory3[2-5]/valid_zones 2>/dev/null
> /sys/devices/system/memory/memory32/valid_zones:Normal
> /sys/devices/system/memory/memory33/valid_zones:Normal Movable
> /sys/devices/system/memory/memory34/valid_zones:Movable
> /sys/devices/system/memory/memory35/valid_zones:Movable
>
> /proc/zoneinfo will now tell
> Node 0, zone   Normal
>   pages free     65441
>         min      165
>         low      230
>         high     295
>         spanned  65536
>         present  65536
> --
> Node 0, zone  Movable
>   pages free     32740
>         min      82
>         low      114
>         high     146
>         spanned  32768
>         present  32768
>
> so both zones have one memblock spanned and present.
>
> Onlining 39 should associate this block to the movable zone
> # echo online > /sys/devices/system/memory/memory39/state
>
> /proc/zoneinfo will now tell
> Node 0, zone   Normal
>   pages free     32765
>         min      80
>         low      112
>         high     144
>         spanned  32768
>         present  32768
> --
> Node 0, zone  Movable
>   pages free     65501
>         min      160
>         low      225
>         high     290
>         spanned  196608
>         present  65536
>
> so we will have a movable zone which spans 6 memblocks, 2 present and 4
> representing a hole.
>
> Offlining both movable blocks will lead to the zone with no present
> pages which is the expected behavior I believe.
> # echo offline > /sys/devices/system/memory/memory39/state
> # echo offline > /sys/devices/system/memory/memory34/state
> # grep -A6 "Movable\|Normal" /proc/zoneinfo
> Node 0, zone   Normal
>   pages free     32735
>         min      90
>         low      122
>         high     154
>         spanned  32768
>         present  32768
> --
> Node 0, zone  Movable
>   pages free     0
>         min      0
>         low      0
>         high     0
>         spanned  196608
>         present  0
>
> Any thoughts, complains, suggestions?
>
> As a bonus we will get a nice cleanup in the memory hotplug codebase.
>  arch/ia64/mm/init.c            |  11 +-
>  arch/powerpc/mm/mem.c          |  12 +-
>  arch/s390/mm/init.c            |  32 +--
>  arch/sh/mm/init.c              |  10 +-
>  arch/x86/mm/init_32.c          |   7 +-
>  arch/x86/mm/init_64.c          |  11 +-
>  drivers/base/memory.c          |  79 +++----
>  drivers/base/node.c            |  58 ++----
>  include/linux/memory_hotplug.h |  40 +++-
>  include/linux/mmzone.h         |  57 +++++-
>  include/linux/node.h           |  35 +++-
>  kernel/memremap.c              |   6 +-
>  mm/compaction.c                |   5 +-
>  mm/memory_hotplug.c            | 455 ++++++++++++++---------------------------
>  mm/page_alloc.c                |  13 +-
>  mm/page_isolation.c            |  26 ++-
>  mm/sparse.c                    |  48 ++++-
>  mm/vmstat.c                    |   4 +-
>  18 files changed, 417 insertions(+), 492 deletions(-)
>
> Shortlog says:
> Michal Hocko (14):
>       mm: remove return value from init_currently_empty_zone
>       mm, memory_hotplug: use node instead of zone in can_online_high_movable
>       mm: drop page_initialized check from get_nid_for_pfn
>       mm, memory_hotplug: get rid of is_zone_device_section
>       mm, memory_hotplug: split up register_one_node
>       mm, memory_hotplug: consider offline memblocks removable
>       mm: consider zone which is not fully populated to have holes
>       mm, compaction: skip over holes in __reset_isolation_suitable
>       mm: __first_valid_page skip over offline pages
>       mm, vmstat: skip reporting offline pages in pagetypeinfo
>       mm, memory_hotplug: do not associate hotadded memory to zones until online
>       mm, memory_hotplug: replace for_device by want_memblock in arch_add_memory
>       mm, memory_hotplug: fix the section mismatch warning
>       mm, memory_hotplug: remove unused cruft after memory hotplug rework
>
> [1] http://lkml.kernel.org/r/20170421120512.23960-1-mhocko@kernel.org
>
>

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