[PATCH v10 03/13] mm/sparsemem: Add helpers track active portions of a section at boot

Dan Williams
2019-06-19T06:06:11Z

Prepare for hot{plug,remove} of sub-ranges of a section by tracking a
sub-section active bitmask, each bit representing a PMD_SIZE span of the
architecture's memory hotplug section size.

The implications of a partially populated section is that pfn_valid()
needs to go beyond a valid_section() check and either determine that the
section is an "early section", or read the sub-section active ranges
from the bitmask. The expectation is that the bitmask (subsection_map)
fits in the same cacheline as the valid_section() / early_section()
data, so the incremental performance overhead to pfn_valid() should be
negligible.

The rationale for using early_section() to short-ciruit the
subsection_map check is that there are legacy code paths that use
pfn_valid() at section granularity before validating the pfn against
pgdat data. So, the early_section() check allows those traditional
assumptions to persist while also permitting subsection_map to tell the
truth for purposes of populating the unused portions of early sections
with PMEM and other ZONE_DEVICE mappings.

Cc: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Logan Gunthorpe <logang@deltatee.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Reported-by: Qian Cai <cai@lca.pw>
Tested-by: Jane Chu <jane.chu@oracle.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
include/linux/mmzone.h | 33 ++++++++++++++++++++++++++++++++-
mm/page_alloc.c | 10 ++++++++--
mm/sparse.c | 35 +++++++++++++++++++++++++++++++++++
3 files changed, 75 insertions(+), 3 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index d081c9a1d25d..c4e8843e283c 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1179,6 +1179,8 @@ struct mem_section_usage {
unsigned long pageblock_flags[0];
};

+void subsection_map_init(unsigned long pfn, unsigned long nr_pages);
+
struct page;
struct page_ext;
struct mem_section {
@@ -1322,12 +1324,40 @@ static inline struct mem_section *__pfn_to_section(unsigned long pfn)

extern int __highest_present_section_nr;

+static inline int subsection_map_index(unsigned long pfn)
+{
+ return (pfn & ~(PAGE_SECTION_MASK)) / PAGES_PER_SUBSECTION;
+}
+
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn)
+{
+ int idx = subsection_map_index(pfn);
+
+ return test_bit(idx, ms->usage->subsection_map);
+}
+#else
+static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn)
+{
+ return 1;
+}
+#endif
+
#ifndef CONFIG_HAVE_ARCH_PFN_VALID
static inline int pfn_valid(unsigned long pfn)
{
+ struct mem_section *ms;
+
if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
return 0;
- return valid_section(__nr_to_section(pfn_to_section_nr(pfn)));
+ ms = __nr_to_section(pfn_to_section_nr(pfn));
+ if (!valid_section(ms))
+ return 0;
+ /*
+ * Traditionally early sections always returned pfn_valid() for
+ * the entire section-sized span.
+ */
+ return early_section(ms) || pfn_section_valid(ms, pfn);
}
#endif

@@ -1359,6 +1389,7 @@ void sparse_init(void);
#define sparse_init() do {} while (0)
#define sparse_index_init(_sec, _nid) do {} while (0)
#define pfn_present pfn_valid
+#define subsection_map_init(_pfn, _nr_pages) do {} while (0)
#endif /* CONFIG_SPARSEMEM */

/*
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8cc091e87200..8e7215fb6976 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7306,12 +7306,18 @@ void __init free_area_init_nodes(unsigned long *max_zone_pfn)
(u64)zone_movable_pfn[i] << PAGE_SHIFT);
}

- /* Print out the early node map */
+ /*
+ * Print out the early node map, and initialize the
+ * subsection-map relative to active online memory ranges to
+ * enable future "sub-section" extensions of the memory map.
+ */
pr_info("Early memory node ranges\n");
- for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid)
+ for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid) {
pr_info(" node %3d: [mem %#018Lx-%#018Lx]\n", nid,
(u64)start_pfn << PAGE_SHIFT,
((u64)end_pfn << PAGE_SHIFT) - 1);
+ subsection_map_init(start_pfn, end_pfn - start_pfn);
+ }

/* Initialise every node */
mminit_verify_pageflags_layout();
diff --git a/mm/sparse.c b/mm/sparse.c
index 2031a0694f35..e9fec3c2f7ec 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -210,6 +210,41 @@ static inline unsigned long first_present_section_nr(void)
return next_present_section_nr(-1);
}

+void subsection_mask_set(unsigned long *map, unsigned long pfn,
+ unsigned long nr_pages)
+{
+ int idx = subsection_map_index(pfn);
+ int end = subsection_map_index(pfn + nr_pages - 1);
+
+ bitmap_set(map, idx, end - idx + 1);
+}
+
+void __init subsection_map_init(unsigned long pfn, unsigned long nr_pages)
+{
+ int end_sec = pfn_to_section_nr(pfn + nr_pages - 1);
+ int i, start_sec = pfn_to_section_nr(pfn);
+
+ if (!nr_pages)
+ return;
+
+ for (i = start_sec; i <= end_sec; i++) {
+ struct mem_section *ms;
+ unsigned long pfns;
+
+ pfns = min(nr_pages, PAGES_PER_SECTION
+ - (pfn & ~PAGE_SECTION_MASK));
+ ms = __nr_to_section(i);
+ subsection_mask_set(ms->usage->subsection_map, pfn, pfns);
+
+ pr_debug("%s: sec: %d pfns: %ld set(%d, %d)\n", __func__, i,
+ pfns, subsection_map_index(pfn),
+ subsection_map_index(pfn + pfns - 1));
+
+ pfn += pfns;
+ nr_pages -= pfns;
+ }
+}
+
/* Record a memory area against a node. */
void __init memory_present(int nid, unsigned long start, unsigned long end)
{