mm/sparse: abstract sparse buffer allocations
Patch series "sparse_init rewrite", v6. In sparse_init() we allocate two large buffers to temporary hold usemap and memmap for the whole machine. However, we can avoid doing that if we changed sparse_init() to operated on per-node bases instead of doing it on the whole machine beforehand. As shown by Baoquan http://lkml.kernel.org/r/20180628062857.29658-1-bhe@redhat.com The buffers are large enough to cause machine stop to boot on small memory systems. Another benefit of these changes is that they also obsolete CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER. This patch (of 5): When struct pages are allocated for sparse-vmemmap VA layout, we first try to allocate one large buffer, and than if that fails allocate struct pages for each section as we go. The code that allocates buffer is uses global variables and is spread across several call sites. Cleanup the code by introducing three functions to handle the global buffer: sparse_buffer_init() initialize the buffer sparse_buffer_fini() free the remaining part of the buffer sparse_buffer_alloc() alloc from the buffer, and if buffer is empty return NULL Define these functions in sparse.c instead of sparse-vmemmap.c because later we will use them for non-vmemmap sparse allocations as well. [akpm@linux-foundation.org: use PTR_ALIGN()] [akpm@linux-foundation.org: s/BUG_ON/WARN_ON/] Link: http://lkml.kernel.org/r/20180712203730.8703-2-pasha.tatashin@oracle.com Signed-off-by:Pavel Tatashin <pasha.tatashin@oracle.com> Tested-by: Michael Ellerman <mpe@ellerman.id.au> [powerpc] Reviewed-by:
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