On 6/2/2021 3:14 PM, David Hildenbrand wrote:

On 02.06.21 13:10, Max Gurtovoy wrote:

quoted

Hotplugged memory has alignmet restrictions. E.g, it disallows all
operations smaller than a sub-section and only allow operations smaller
than a section for SPARSEMEM_VMEMMAP. Export the alignment restrictions
for mhp users.

Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
---
  include/linux/memory_hotplug.h |  5 +++++
  mm/memory_hotplug.c            | 33 +++++++++++++++++++--------------
  2 files changed, 24 insertions(+), 14 deletions(-)

diff --git a/include/linux/memory_hotplug.h 

b/include/linux/memory_hotplug.h
index 28f32fd00fe9..c55a9049b11e 100644

--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h

@@ -76,6 +76,7 @@ struct mhp_params {

    bool mhp_range_allowed(u64 start, u64 size, bool need_mapping);
  struct range mhp_get_pluggable_range(bool need_mapping);
+unsigned long mhp_get_min_align(void);
    /*
   * Zone resizing functions

@@ -248,6 +249,10 @@ void mem_hotplug_done(void);

      ___page;                \
   })
  +static inline unsigned long mhp_get_min_align(void)
+{
+    return 0;
+}
  static inline unsigned zone_span_seqbegin(struct zone *zone)
  {
      return 0;

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 9e86e9ee0a10..161bb6704a9b 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c

@@ -270,24 +270,29 @@ void __init 

register_page_bootmem_info_node(struct pglist_data *pgdat)
  }
  #endif /* CONFIG_HAVE_BOOTMEM_INFO_NODE */
  +/*
+ * Disallow all operations smaller than a sub-section and only
+ * allow operations smaller than a section for
+ * SPARSEMEM_VMEMMAP. Note that check_hotplug_memory_range()
+ * enforces a larger memory_block_size_bytes() granularity for
+ * memory that will be marked online, so this check should only
+ * fire for direct arch_{add,remove}_memory() users outside of
+ * add_memory_resource().
+ */
+unsigned long mhp_get_min_align(void)
+{
+    if (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP))
+        return PAGES_PER_SUBSECTION;
+    return PAGES_PER_SECTION;
+}
+EXPORT_SYMBOL_GPL(mhp_get_min_align);

We have to main interfaces to "hotplug" memory:

a) add_memory() and friends for System RAM, which have memory block 
alignment requirements.

b) memremap_pages(), which has the alignemnt requirements you mention 
here.

I feel like what you need would better be exposed in mm/memremap.c, 
for example, via "memremap_min_alignment" so it matches the 
"memremap_pages" semantics.

And then, memremap_pages() is only available with CONFIG_ZONE_DEVICE, 
which depends on SPARSEMEM_VMEMMAP. So you'll always have 
PAGES_PER_SUBSECTION.

I can already spot "memremap_compat_align", maybe you can reuse that 
or handle it accordingly in there?

Yes I think that since subsection is aligned to PAGE_SIZE I can do:

size_t pci_p2pdma_align_size(size_t size)
{
         unsigned long min_align;

         min_align = memremap_compat_align();
         if (!IS_ALIGNED(size, min_align))
                 return ALIGN_DOWN(size, min_align);

         return size;
}


thoughts ?

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