Commit 4c29700e authored by Vincent Whitchurch's avatar Vincent Whitchurch Committed by Linus Torvalds

mm/sparse: consistently do not zero memmap

sparsemem without VMEMMAP has two allocation paths to allocate the
memory needed for its memmap (done in sparse_mem_map_populate()).

In one allocation path (sparse_buffer_alloc() succeeds), the memory is
not zeroed (since it was previously allocated with
memblock_alloc_try_nid_raw()).

In the other allocation path (sparse_buffer_alloc() fails and
sparse_mem_map_populate() falls back to memblock_alloc_try_nid()), the
memory is zeroed.

AFAICS this difference does not appear to be on purpose.  If the code is
supposed to work with non-initialized memory (__init_single_page() takes
care of zeroing the struct pages which are actually used), we should
consistently not zero the memory, to avoid masking bugs.

( 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. )

Michal:
 "the main user visible problem is a memory wastage. The overal amount
  of memory should be small. I wouldn't call it stable material."

Link: http://lkml.kernel.org/r/20191030131122.8256-1-vincent.whitchurch@axis.comSigned-off-by: default avatarVincent Whitchurch <vincent.whitchurch@axis.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarOscar Salvador <osalvador@suse.de>
Reviewed-by: default avatarPavel Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c5e79ef5
......@@ -458,7 +458,7 @@ struct page __init *__populate_section_memmap(unsigned long pfn,
if (map)
return map;
map = memblock_alloc_try_nid(size,
map = memblock_alloc_try_nid_raw(size,
PAGE_SIZE, addr,
MEMBLOCK_ALLOC_ACCESSIBLE, nid);
if (!map)
......
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