diff options
Diffstat (limited to 'Documentation/admin-guide/mm')
| -rw-r--r-- | Documentation/admin-guide/mm/hugetlbpage.rst | 11 | ||||
| -rw-r--r-- | Documentation/admin-guide/mm/memory-hotplug.rst | 13 | ||||
| -rw-r--r-- | Documentation/admin-guide/mm/pagemap.rst | 2 | ||||
| -rw-r--r-- | Documentation/admin-guide/mm/userfaultfd.rst | 3 |
4 files changed, 28 insertions, 1 deletions
diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst index f7b1c7462991..8abaeb144e44 100644 --- a/Documentation/admin-guide/mm/hugetlbpage.rst +++ b/Documentation/admin-guide/mm/hugetlbpage.rst @@ -60,6 +60,10 @@ HugePages_Surp the pool above the value in ``/proc/sys/vm/nr_hugepages``. The maximum number of surplus huge pages is controlled by ``/proc/sys/vm/nr_overcommit_hugepages``. + Note: When the feature of freeing unused vmemmap pages associated + with each hugetlb page is enabled, the number of surplus huge pages + may be temporarily larger than the maximum number of surplus huge + pages when the system is under memory pressure. Hugepagesize is the default hugepage size (in Kb). Hugetlb @@ -80,6 +84,10 @@ returned to the huge page pool when freed by a task. A user with root privileges can dynamically allocate more or free some persistent huge pages by increasing or decreasing the value of ``nr_hugepages``. +Note: When the feature of freeing unused vmemmap pages associated with each +hugetlb page is enabled, we can fail to free the huge pages triggered by +the user when ths system is under memory pressure. Please try again later. + Pages that are used as huge pages are reserved inside the kernel and cannot be used for other purposes. Huge pages cannot be swapped out under memory pressure. @@ -145,6 +153,9 @@ default_hugepagesz will all result in 256 2M huge pages being allocated. Valid default huge page size is architecture dependent. +hugetlb_free_vmemmap + When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set, this enables freeing + unused vmemmap pages associated with each HugeTLB page. When multiple huge page sizes are supported, ``/proc/sys/vm/nr_hugepages`` indicates the current number of pre-allocated huge pages of the default size. diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst index 05d51d2d8beb..c6bae2d77160 100644 --- a/Documentation/admin-guide/mm/memory-hotplug.rst +++ b/Documentation/admin-guide/mm/memory-hotplug.rst @@ -357,6 +357,19 @@ creates ZONE_MOVABLE as following. Unfortunately, there is no information to show which memory block belongs to ZONE_MOVABLE. This is TBD. + Memory offlining can fail when dissolving a free huge page on ZONE_MOVABLE + and the feature of freeing unused vmemmap pages associated with each hugetlb + page is enabled. + + This can happen when we have plenty of ZONE_MOVABLE memory, but not enough + kernel memory to allocate vmemmmap pages. We may even be able to migrate + huge page contents, but will not be able to dissolve the source huge page. + This will prevent an offline operation and is unfortunate as memory offlining + is expected to succeed on movable zones. Users that depend on memory hotplug + to succeed for movable zones should carefully consider whether the memory + savings gained from this feature are worth the risk of possibly not being + able to offline memory in certain situations. + .. note:: Techniques that rely on long-term pinnings of memory (especially, RDMA and vfio) are fundamentally problematic with ZONE_MOVABLE and, therefore, memory diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst index 340a5aee9b80..fb578fbbb76c 100644 --- a/Documentation/admin-guide/mm/pagemap.rst +++ b/Documentation/admin-guide/mm/pagemap.rst @@ -21,6 +21,8 @@ There are four components to pagemap: * Bit 55 pte is soft-dirty (see :ref:`Documentation/admin-guide/mm/soft-dirty.rst <soft_dirty>`) * Bit 56 page exclusively mapped (since 4.2) + * Bit 57 pte is uffd-wp write-protected (since 5.13) (see + :ref:`Documentation/admin-guide/mm/userfaultfd.rst <userfaultfd>`) * Bits 57-60 zero * Bit 61 page is file-page or shared-anon (since 3.5) * Bit 62 page swapped diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst index 3aa38e8b8361..6528036093e1 100644 --- a/Documentation/admin-guide/mm/userfaultfd.rst +++ b/Documentation/admin-guide/mm/userfaultfd.rst @@ -77,7 +77,8 @@ events, except page fault notifications, may be generated: - ``UFFD_FEATURE_MINOR_HUGETLBFS`` indicates that the kernel supports ``UFFDIO_REGISTER_MODE_MINOR`` registration for hugetlbfs virtual memory - areas. + areas. ``UFFD_FEATURE_MINOR_SHMEM`` is the analogous feature indicating + support for shmem virtual memory areas. The userland application should set the feature flags it intends to use when invoking the ``UFFDIO_API`` ioctl, to request that those features be |