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.
