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    SubjectRe: [PATCH v1] memory-hotplug.rst: complete admin-guide overhaul
    On Tue, Jun 08, 2021 at 03:04:19PM +0200, David Hildenbrand wrote:

    ...

    > > > +--------------
    > > > -You can offline a memory block by using the same sysfs interface that was used
    > > > -in memory onlining::
    > > > +We usually expect that a large portion of available system RAM will actually
    > > > +be consumed by user space, either directly or indirectly via the page cache. In
    > > > +the normal case, ZONE_MOVABLE can be used when allocating such pages just fine.
    > > > - % echo offline > /sys/devices/system/memory/memoryXXX/state
    > > > +With that in mind, it makes sense that we can have a big portion of system RAM
    > > > +managed by ZONE_MOVABLE. However, there are some things to consider when
    > > > +using ZONE_MOVABLE, especially when fine-tuning zone ratios:
    > > > -If offline succeeds, the state of the memory block is changed to be "offline".
    > > > -If it fails, some error core (like -EBUSY) will be returned by the kernel.
    > > > -Even if a memory block does not belong to ZONE_MOVABLE, you can try to offline
    > > > -it. If it doesn't contain 'unmovable' memory, you'll get success.
    > > > +- Having a lot of offline memory blocks. Even offline memory blocks consume
    > > > + memory for metadata and page tables in the direct map; having a lot of
    > > > + offline memory blocks is not a typical case, though.
    > > > +
    > > > +- Memory ballooning. Some memory ballooning implementations, such as
    > > > + the Hyper-V balloon, the XEN balloon, the vbox balloon and the VMWare
    > >
    > > So, everyone except virtio-mem? ;-)
    >
    > Well, virtio-mem does not classify as memory balloon in that sense, as it
    > only operates on own device memory ;)
    >
    > virtio-balloon and pseries CMM support balloon compaction.
    >
    > > I'd drop the names because if some of those will implement balloon
    > > compaction they surely will forget to update the docs.

    > I can do the opposite and mention the ones that already do. Some most
    > probably will never support it.
    >
    > "Memory ballooning without balloon compaction is incompatible with
    > ZONE_MOVABLE. Only some implementations, such as virtio-balloon and pseries
    > CMM, fully support balloon compaction."

    Sounds good.

    --
    Sincerely yours,
    Mike.

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