diff options
Diffstat (limited to 'Documentation/admin-guide/mm/memory-hotplug.rst')
| -rw-r--r-- | Documentation/admin-guide/mm/memory-hotplug.rst | 22 |
1 files changed, 16 insertions, 6 deletions
diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst index 33c886f3d198..0207f8725142 100644 --- a/Documentation/admin-guide/mm/memory-hotplug.rst +++ b/Documentation/admin-guide/mm/memory-hotplug.rst @@ -603,17 +603,18 @@ ZONE_MOVABLE, especially when fine-tuning zone ratios: 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 without balloon compaction is incompatible with - ZONE_MOVABLE. Only some implementations, such as virtio-balloon and - pseries CMM, fully support balloon compaction. +- Memory ballooning without support for balloon memory migration is incompatible + with ZONE_MOVABLE. Only some implementations, such as virtio-balloon and + pseries CMM, fully support balloon memory migration. - Further, the CONFIG_BALLOON_COMPACTION kernel configuration option might be + Further, the CONFIG_BALLOON_MIGRATION kernel configuration option might be disabled. In that case, balloon inflation will only perform unmovable allocations and silently create a zone imbalance, usually triggered by inflation requests from the hypervisor. -- Gigantic pages are unmovable, resulting in user space consuming a - lot of unmovable memory. +- Gigantic pages are unmovable when an architecture does not support + huge page migration and/or the ``movable_gigantic_pages`` sysctl is false. + See Documentation/admin-guide/sysctl/vm.rst for more info on this sysctl. - Huge pages are unmovable when an architectures does not support huge page migration, resulting in a similar issue as with gigantic pages. @@ -672,6 +673,15 @@ block might fail: - Concurrent activity that operates on the same physical memory area, such as allocating gigantic pages, can result in temporary offlining failures. +- When an admin sets the ``movable_gigantic_pages`` sysctl to true, gigantic + pages are allowed in ZONE_MOVABLE. This only allows migratable gigantic + pages to be allocated; however, if there are no eligible destination gigantic + pages at offline, the offlining operation will fail. + + Users leveraging ``movable_gigantic_pages`` should weigh the value of + ZONE_MOVABLE for increasing the reliability of gigantic page allocation + against the potential loss of hot-unplug reliability. + - Out of memory when dissolving huge pages, especially when HugeTLB Vmemmap Optimization (HVO) is enabled. |