The patch titled
Subject: mm/sparse.c: do not waste pre allocated memmap space
has been added to the -mm tree. Its filename is
mm-sparse-do-not-waste-pre-allocated-memmap-space.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-sparse-do-not-waste-pre-allocated-memmap-space.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-sparse-do-not-waste-pre-allocated-memmap-space.patch
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From: Michal Hocko <mhocko@xxxxxxxx>
Subject: mm/sparse.c: do not waste pre allocated memmap space
Vincent has noticed [1] that there is something unusual with the memmap
allocations going on on his platform
: 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.
The underlying problem is that although sparse_buffer_init allocates
enough memory for all sections on the node sparse_buffer_alloc is not able
to consume them due to mismatch in the expected allocation alignement.
While sparse_buffer_init preallocation uses the PAGE_SIZE alignment the
real memmap has to be aligned to section_map_size() this results in a
wasted initial chunk of the preallocated memmap and unnecessary fallback
allocation for a section.
While we are at it also change __populate_section_memmap to align to the
requested size because at least VMEMMAP has constrains to have memmap
properly aligned.
[1] http://lkml.kernel.org/r/20191030131122.8256-1-vincent.whitchurch@xxxxxxxx
Link: http://lkml.kernel.org/r/20191119092642.31799-1-mhocko@xxxxxxxxxx
Fixes: 35fd1eb1e821 ("mm/sparse: abstract sparse buffer allocations")
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Reported-by: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx>
Debugged-by: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Oscar Salvador <OSalvador@xxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/sparse.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
--- a/mm/sparse.c~mm-sparse-do-not-waste-pre-allocated-memmap-space
+++ a/mm/sparse.c
@@ -458,8 +458,7 @@ struct page __init *__populate_section_m
if (map)
return map;
- map = memblock_alloc_try_nid(size,
- PAGE_SIZE, addr,
+ map = memblock_alloc_try_nid(size, size, addr,
MEMBLOCK_ALLOC_ACCESSIBLE, nid);
if (!map)
panic("%s: Failed to allocate %lu bytes align=0x%lx nid=%d from=%pa\n",
@@ -482,8 +481,13 @@ static void __init sparse_buffer_init(un
{
phys_addr_t addr = __pa(MAX_DMA_ADDRESS);
WARN_ON(sparsemap_buf); /* forgot to call sparse_buffer_fini()? */
+ /*
+ * Pre-allocated buffer is mainly used by __populate_section_memmap
+ * and we want it to be properly aligned to the section size - this is
+ * especially the case for VMEMMAP which maps memmap to PMDs
+ */
sparsemap_buf =
- memblock_alloc_try_nid_raw(size, PAGE_SIZE,
+ memblock_alloc_try_nid_raw(size, section_map_size(),
addr,
MEMBLOCK_ALLOC_ACCESSIBLE, nid);
sparsemap_buf_end = sparsemap_buf + size;
_
Patches currently in -mm which might be from mhocko@xxxxxxxx are
mm-sparse-do-not-waste-pre-allocated-memmap-space.patch
