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Subject[PATCH] sparse: Track the boundaries of memory sections for accurate checks
Date
When sparse memory model is used an array of memory sections is created to
track each block of contiguous physical pages. Each element of this array
contains PAGES_PER_SECTION pages. During the creation of this array the actual
boundaries of the memory block is lost, so the whole block is either considered
as present or not.

pfn_valid() in the sparse memory configuration checks which memory sections the
pfn belongs to then checks whether it's present or not. This yields sub-optimal
results when the available memory doesn't cover the whole memory section,
because pfn_valid will return 'true' even for the unavailable pfns at the
boundaries of the memory section.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Yaowei Bai <baiyaowei@cmss.chinamobile.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Joe Perches <joe@perches.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Anthony Liguori <aliguori@amazon.com>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
Signed-off-by: Jan H. Schönherr <jschoenh@amazon.de>
---
include/linux/mmzone.h | 22 ++++++++++++++++------
mm/sparse.c | 37 ++++++++++++++++++++++++++++++++++++-
2 files changed, 52 insertions(+), 7 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 02069c2..f76a0e1 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1067,8 +1067,12 @@ struct mem_section {
* section. (see page_ext.h about this.)
*/
struct page_ext *page_ext;
- unsigned long pad;
+ unsigned long pad[3];
#endif
+
+ unsigned long first_pfn;
+ unsigned long last_pfn;
+
/*
* WARNING: mem_section must be a power-of-2 in size for the
* calculation and use of SECTION_ROOT_MASK to make sense.
@@ -1140,23 +1144,29 @@ static inline int valid_section_nr(unsigned long nr)

static inline struct mem_section *__pfn_to_section(unsigned long pfn)
{
+ if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
+ return NULL;
+
return __nr_to_section(pfn_to_section_nr(pfn));
}

#ifndef CONFIG_HAVE_ARCH_PFN_VALID
static inline int pfn_valid(unsigned long pfn)
{
- if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
+ struct mem_section *ms;
+
+ ms = __pfn_to_section(pfn);
+
+ if (ms && !(ms->first_pfn <= pfn && ms->last_pfn >= pfn))
return 0;
- return valid_section(__nr_to_section(pfn_to_section_nr(pfn)));
+
+ return valid_section(ms);
}
#endif

static inline int pfn_present(unsigned long pfn)
{
- if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
- return 0;
- return present_section(__nr_to_section(pfn_to_section_nr(pfn)));
+ return present_section(__pfn_to_section(pfn));
}

/*
diff --git a/mm/sparse.c b/mm/sparse.c
index 5d0cf45..3c91837 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -166,24 +166,59 @@ void __meminit mminit_validate_memmodel_limits(unsigned long *start_pfn,
}
}

+static int __init
+overlaps(u64 start1, u64 end1, u64 start2, u64 end2)
+{
+ u64 start, end;
+
+ start = max(start1, start2);
+ end = min(end1, end2);
+ return start <= end;
+}
+
/* Record a memory area against a node. */
void __init memory_present(int nid, unsigned long start, unsigned long end)
{
+ unsigned long first_pfn = start;
unsigned long pfn;

start &= PAGE_SECTION_MASK;
mminit_validate_memmodel_limits(&start, &end);
for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION) {
unsigned long section = pfn_to_section_nr(pfn);
+ unsigned long last_pfn = min(pfn + PAGES_PER_SECTION, end) - 1;
struct mem_section *ms;

sparse_index_init(section, nid);
set_section_nid(section, nid);

ms = __nr_to_section(section);
- if (!ms->section_mem_map)
+ if (!ms->section_mem_map) {
ms->section_mem_map = sparse_encode_early_nid(nid) |
SECTION_MARKED_PRESENT;
+ } else {
+ /* Merge the two regions */
+ WARN_ON(sparse_early_nid(ms) != nid);
+
+ /*
+ * If they don't overlap there will be a hole in
+ * between where meta-data says it's valid even though
+ * it's not.
+ */
+ if (!overlaps(first_pfn, last_pfn + 1,
+ ms->first_pfn, ms->last_pfn + 1)) {
+ pr_info("Merging non-contiguous pfn ranges 0x%lx-0x%lx and 0x%lx-0x%lx\n",
+ ms->first_pfn, ms->last_pfn,
+ first_pfn, last_pfn);
+ }
+ first_pfn = min(first_pfn, ms->first_pfn);
+ last_pfn = max(last_pfn, ms->last_pfn);
+ }
+
+ ms->first_pfn = first_pfn;
+ ms->last_pfn = last_pfn;
+
+ first_pfn = pfn + PAGES_PER_SECTION;
}
}

--
2.8.2
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