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-rw-r--r--include/linux/mmzone.h20
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)
{