On Sat 23-06-12 23:52:52, Gavin Shan wrote:
> Platforms like PPC might need two level mem_section for SPARSEMEM
> with enabled CONFIG_SPARSEMEM_EXTREME. On the other hand, the
> memory section descriptor might be allocated from bootmem allocator
> with PAGE_SIZE alignment. In order to fully utilize the memory chunk
> allocated from bootmem allocator, it'd better to assure memory
> sector descriptor won't run across the boundary (PAGE_SIZE).
Why? The memory is continuous, right?
>
> The patch introduces the check on size of "struct mm_section" to
> assure that.
>
> Signed-off-by: Gavin Shan <shangw@xxxxxxxxxxxxxxxxxx>
> ---
> mm/sparse.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 6a4bf91..afd0998 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -63,6 +63,15 @@ static struct mem_section noinline __init_refok *sparse_index_alloc(int nid)
> unsigned long array_size = SECTIONS_PER_ROOT *
> sizeof(struct mem_section);
>
> + /*
> + * The root memory section descriptor might be allocated
> + * from bootmem, which has minimal memory chunk requirement
> + * of page. In order to fully utilize the memory, the sparse
> + * memory section descriptor shouldn't run across the boundary
> + * that bootmem allocator has.
> + */
> + BUILD_BUG_ON(PAGE_SIZE % sizeof(struct mem_section));
> +
> if (slab_is_available()) {
> if (node_state(nid, N_HIGH_MEMORY))
> section = kmalloc_node(array_size, GFP_KERNEL, nid);
> --
> 1.7.9.5
>
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--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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