On Wed, Oct 30, 2019 at 02:29:58PM +0100, Michal Hocko wrote: > On Wed 30-10-19 14:11:22, Vincent Whitchurch wrote: > > (I noticed this because on my ARM64 platform, with 1 GiB of memory the > > first [and only] section is allocated from the zeroing path while with > > 2 GiB of memory the first 1 GiB section is allocated from the > > non-zeroing path.) > > Do I get it right that sparse_buffer_init couldn't allocate memmap for > the full node for some reason and so sparse_init_nid would have to > allocate one for each memory section? Not quite. The sparsemap_buf is successfully allocated with the correct size in sparse_buffer_init(), but sparse_buffer_alloc() fails to allocate the same size from it. The reason it fails is that sparse_buffer_alloc() for some reason wants to return a pointer which is aligned to the allocation size. But the sparsemap_buf was only allocated with PAGE_SIZE alignment so there's not enough space to align it. I don't understand the reason for this alignment requirement since the fallback path also allocates with PAGE_SIZE alignment. I'm guessing the alignment is for the VMEMAP code which also uses sparse_buffer_alloc()?
