Commit 09dbcf42 authored Nov 30, 2019 by Michal Hocko Committed by Linus Torvalds Dec 01, 2019

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@axis.com

[akpm@linux-foundation.org: tweak layout, per David]
Link: http://lkml.kernel.org/r/20191119092642.31799-1-mhocko@kernel.org


Fixes: 35fd1eb1 ("mm/sparse: abstract sparse buffer allocations")
Signed-off-by: Michal Hocko <mhocko@suse.com>
Reported-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Debugged-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Oscar Salvador <OSalvador@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 030eab4f

mm/sparse.c

+8 −6

Original line number	Original line	Diff line number	Diff line
	@@ -458,8 +458,7 @@ struct page __init *__populate_section_memmap(unsigned long pfn,
	if (map)		if (map)
	return map;		return map;

	map = memblock_alloc_try_nid_raw(size,		map = memblock_alloc_try_nid_raw(size, size, addr,
	PAGE_SIZE, addr,
	MEMBLOCK_ALLOC_ACCESSIBLE, nid);		MEMBLOCK_ALLOC_ACCESSIBLE, nid);
	if (!map)		if (!map)
	panic("%s: Failed to allocate %lu bytes align=0x%lx nid=%d from=%pa\n",		panic("%s: Failed to allocate %lu bytes align=0x%lx nid=%d from=%pa\n",
	@@ -482,10 +481,13 @@ static void __init sparse_buffer_init(unsigned long size, int nid)
	{		{
	phys_addr_t addr = __pa(MAX_DMA_ADDRESS);		phys_addr_t addr = __pa(MAX_DMA_ADDRESS);
	WARN_ON(sparsemap_buf); /* forgot to call sparse_buffer_fini()? */		WARN_ON(sparsemap_buf); /* forgot to call sparse_buffer_fini()? */
	sparsemap_buf =		/*
	memblock_alloc_try_nid_raw(size, PAGE_SIZE,		* Pre-allocated buffer is mainly used by __populate_section_memmap
	addr,		* and we want it to be properly aligned to the section size - this is
	MEMBLOCK_ALLOC_ACCESSIBLE, nid);		* especially the case for VMEMMAP which maps memmap to PMDs
			*/
			sparsemap_buf = memblock_alloc_try_nid_raw(size, section_map_size(),
			addr, MEMBLOCK_ALLOC_ACCESSIBLE, nid);
	sparsemap_buf_end = sparsemap_buf + size;		sparsemap_buf_end = sparsemap_buf + size;
	}		}

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