Re: [PATCH 2/3] mm/page_ext: support early allocation for SPARSEMEM

[Chris Down <chris@chrisdown.name>]

Hi Muchun,

This looks good to me in general, I only have a few small things.

Muchun Song writes:
>-	/*
>-	 * page_owner must be initialized after buddy is ready, and also after
>-	 * slab is ready so that stack_depot_init() works properly
>-	 */
>-	page_ext_init_flatmem_late();

Not a big deal, but this means that on FLATMEM the init callbacks now run
after vmalloc_init() rather than straight after kmem_cache_init(). I can't
see anything that depends on the old place, but FLATMEM isn't what the
patch is about, so it'd be good to say in the changelog that this moves.

>+	if (!slab_is_available()) {
>+		addr = memblock_alloc_try_nid(size, PAGE_SIZE, 0,
>+					      MEMBLOCK_ALLOC_ACCESSIBLE, nid);

Maybe this should pass __pa(MAX_DMA_ADDRESS) as min_addr, like
alloc_node_page_ext() does, so that the tables stay out of ZONE_DMA when
there's room elsewhere?

>+	page = virt_to_page(addr);
>+	if (PageReserved(page)) {
>+		memmap_boot_pages_add(-nr_pages);
>+		kmemleak_free_part_phys(__pa(addr), table_size);
>+		free_reserved_area(addr, addr + table_size, -1, "page_ext");
>+		return;

free_reserved_area() prints "Freeing page_ext memory" when it's given a
name, and this runs once for every section, so offlining a few gigabytes
would put dozens of those in the log. I think it should pass NULL instead.

Did you manage to get this branch to run, by the way? KMSAN is the only
user of need_early, and from a quick check offlining a memory block on a
KMSAN kernel fails with EBUSY, presumably because the metadata pages can't
be migrated, so I couldn't exercise it myself.

Once the changelog and the log message are fixed, please feel free to add:

Reviewed-by: Chris Down <chris@chrisdown.name>

Thanks!

Chris