Merge branch 'akpm' (patches from Andrew)

Merge more updates from Andrew Morton:
 "The remainder of the main mm/ queue.

  143 patches.

  Subsystems affected by this patch series (all mm): pagecache, hugetlb,
  userfaultfd, vmscan, compaction, migration, cma, ksm, vmstat, mmap,
  kconfig, util, memory-hotplug, zswap, zsmalloc, highmem, cleanups, and
  kfence"

* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (143 commits)
  kfence: use power-efficient work queue to run delayed work
  kfence: maximize allocation wait timeout duration
  kfence: await for allocation using wait_event
  kfence: zero guard page after out-of-bounds access
  mm/process_vm_access.c: remove duplicate include
  mm/mempool: minor coding style tweaks
  mm/highmem.c: fix coding style issue
  btrfs: use memzero_page() instead of open coded kmap pattern
  iov_iter: lift memzero_page() to highmem.h
  mm/zsmalloc: use BUG_ON instead of if condition followed by BUG.
  mm/zswap.c: switch from strlcpy to strscpy
  arm64/Kconfig: introduce ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
  x86/Kconfig: introduce ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
  mm,memory_hotplug: add kernel boot option to enable memmap_on_memory
  acpi,memhotplug: enable MHP_MEMMAP_ON_MEMORY when supported
  mm,memory_hotplug: allocate memmap from the added memory range
  mm,memory_hotplug: factor out adjusting present pages into adjust_present_page_count()
  mm,memory_hotplug: relax fully spanned sections check
  drivers/base/memory: introduce memory_block_{online,offline}
  mm/memory_hotplug: remove broken locking of zone PCP structures during hot remove
  ...

1 files changed, 16 insertions, 4 deletions

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 3b2205741048..917bd6c604d5 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -407,8 +407,13 @@ enum zone_type {
 	 * to increase the number of THP/huge pages. Notable special cases are:
 	 *
 	 * 1. Pinned pages: (long-term) pinning of movable pages might
-	 *    essentially turn such pages unmovable. Memory offlining might
-	 *    retry a long time.
+	 *    essentially turn such pages unmovable. Therefore, we do not allow
+	 *    pinning long-term pages in ZONE_MOVABLE. When pages are pinned and
+	 *    faulted, they come from the right zone right away. However, it is
+	 *    still possible that address space already has pages in
+	 *    ZONE_MOVABLE at the time when pages are pinned (i.e. user has
+	 *    touches that memory before pinning). In such case we migrate them
+	 *    to a different zone. When migration fails - pinning fails.
 	 * 2. memblock allocations: kernelcore/movablecore setups might create
 	 *    situations where ZONE_MOVABLE contains unmovable allocations
 	 *    after boot. Memory offlining and allocations fail early.
@@ -427,6 +432,15 @@ enum zone_type {
 	 *    techniques might use alloc_contig_range() to hide previously
 	 *    exposed pages from the buddy again (e.g., to implement some sort
 	 *    of memory unplug in virtio-mem).
+	 * 6. ZERO_PAGE(0), kernelcore/movablecore setups might create
+	 *    situations where ZERO_PAGE(0) which is allocated differently
+	 *    on different platforms may end up in a movable zone. ZERO_PAGE(0)
+	 *    cannot be migrated.
+	 * 7. Memory-hotplug: when using memmap_on_memory and onlining the
+	 *    memory to the MOVABLE zone, the vmemmap pages are also placed in
+	 *    such zone. Such pages cannot be really moved around as they are
+	 *    self-stored in the range, but they are treated as movable when
+	 *    the range they describe is about to be offlined.
 	 *
 	 * In general, no unmovable allocations that degrade memory offlining
 	 * should end up in ZONE_MOVABLE. Allocators (like alloc_contig_range())
@@ -1383,10 +1397,8 @@ static inline int online_section_nr(unsigned long nr)
 
 #ifdef CONFIG_MEMORY_HOTPLUG
 void online_mem_sections(unsigned long start_pfn, unsigned long end_pfn);
-#ifdef CONFIG_MEMORY_HOTREMOVE
 void offline_mem_sections(unsigned long start_pfn, unsigned long end_pfn);
 #endif
-#endif
 
 static inline struct mem_section *__pfn_to_section(unsigned long pfn)
 {