Re: [PATCH v7 6/7] mm/memory_hotplug: Embed vmem_altmap details in memory block

["Verma, Vishal L" <vishal.l.verma@intel.com>]

On Tue, 2023-08-01 at 10:11 +0530, Aneesh Kumar K.V wrote:
> With memmap on memory, some architecture needs more details w.r.t altmap
> such as base_pfn, end_pfn, etc to unmap vmemmap memory. Instead of
> computing them again when we remove a memory block, embed vmem_altmap
> details in struct memory_block if we are using memmap on memory block
> feature.
> 
> Acked-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> ---
>  drivers/base/memory.c  | 27 +++++++++++++--------
>  include/linux/memory.h |  8 ++----
>  mm/memory_hotplug.c    | 55 ++++++++++++++++++++++++++----------------
>  3 files changed, 53 insertions(+), 37 deletions(-)
> 
<snip>

> @@ -2136,10 +2148,10 @@ EXPORT_SYMBOL(try_offline_node);
>  
>  static int __ref try_remove_memory(u64 start, u64 size)
>  {
> -       struct vmem_altmap mhp_altmap = {};
> -       struct vmem_altmap *altmap = NULL;
> -       unsigned long nr_vmemmap_pages;
> +       int ret;

Minor nit - there is already an 'int rc' below - just use that, or
rename it to 'ret' if that's better for consistency.

> +       struct memory_block *mem;
>         int rc = 0, nid = NUMA_NO_NODE;
> +       struct vmem_altmap *altmap = NULL;
>  
>         BUG_ON(check_hotplug_memory_range(start, size));
>  
> @@ -2161,25 +2173,20 @@ static int __ref try_remove_memory(u64 start, u64 size)
>          * the same granularity it was added - a single memory block.
>          */
>         if (mhp_memmap_on_memory()) {
> -               nr_vmemmap_pages = walk_memory_blocks(start, size, NULL,
> -                                                     get_nr_vmemmap_pages_cb);
> -               if (nr_vmemmap_pages) {
> +               ret = walk_memory_blocks(start, size, &mem, test_has_altmap_cb);
> +               if (ret) {
>                         if (size != memory_block_size_bytes()) {
>                                 pr_warn("Refuse to remove %#llx - %#llx,"
>                                         "wrong granularity\n",
>                                         start, start + size);
>                                 return -EINVAL;
>                         }
> -
> +                       altmap = mem->altmap;
>                         /*
> -                        * Let remove_pmd_table->free_hugepage_table do the
> -                        * right thing if we used vmem_altmap when hot-adding
> -                        * the range.
> +                        * Mark altmap NULL so that we can add a debug
> +                        * check on memblock free.
>                          */
> -                       mhp_altmap.base_pfn = PHYS_PFN(start);
> -                       mhp_altmap.free = nr_vmemmap_pages;
> -                       mhp_altmap.alloc = nr_vmemmap_pages;
> -                       altmap = &mhp_altmap;
> +                       mem->altmap = NULL;
>                 }
>         }
>