On some machines, the normal zone can have a large memory hole like
below memory layout, and we can see the range from 0x100000000 to
0x1800000000 is a hole. So when isolating some migratable pages, the
scanner can meet the hole and it will take more time to skip the large
hole. From my measurement, I can see the isolation scanner will take
80us ~ 100us to skip the large hole [0x100000000 - 0x1800000000].
So adding a new helper to fast search next online memory section
to skip the large hole can help to find next suitable pageblock
efficiently. With this patch, I can see the large hole scanning only
takes < 1us.
[ 0.000000] Zone ranges:
[ 0.000000] DMA [mem 0x0000000040000000-0x00000000ffffffff]
[ 0.000000] DMA32 empty
[ 0.000000] Normal [mem 0x0000000100000000-0x0000001fa7ffffff]
[ 0.000000] Movable zone start for each node
[ 0.000000] Early memory node ranges
[ 0.000000] node 0: [mem 0x0000000040000000-0x0000000fffffffff]
[ 0.000000] node 0: [mem 0x0000001800000000-0x0000001fa3c7ffff]
[ 0.000000] node 0: [mem 0x0000001fa3c80000-0x0000001fa3ffffff]
[ 0.000000] node 0: [mem 0x0000001fa4000000-0x0000001fa402ffff]
[ 0.000000] node 0: [mem 0x0000001fa4030000-0x0000001fa40effff]
[ 0.000000] node 0: [mem 0x0000001fa40f0000-0x0000001fa73cffff]
[ 0.000000] node 0: [mem 0x0000001fa73d0000-0x0000001fa745ffff]
[ 0.000000] node 0: [mem 0x0000001fa7460000-0x0000001fa746ffff]
[ 0.000000] node 0: [mem 0x0000001fa7470000-0x0000001fa758ffff]
[ 0.000000] node 0: [mem 0x0000001fa7590000-0x0000001fa7ffffff]
Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
---
Changes from v2:
- Simplify the function suggested by David.
- Collect acked tag from David and Ying. Thanks.
Changes from v1:
- Fix building errors if CONFIG_SPARSEMEM is not selected.
- Use NR_MEM_SECTIONS instead of '-1' per Huang Ying.
---
mm/compaction.c | 35 ++++++++++++++++++++++++++++++++++-
1 file changed, 34 insertions(+), 1 deletion(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index 3398ef3a55fe..0b2680b075fd 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -229,6 +229,33 @@ static void reset_cached_positions(struct zone *zone)
pageblock_start_pfn(zone_end_pfn(zone) - 1);
}
+#ifdef CONFIG_SPARSEMEM
+/*
+ * If the PFN falls into an offline section, return the start PFN of the
+ * next online section. If the PFN falls into an online section or if
+ * there is no next online section, return 0.
+ */
+static unsigned long skip_offline_sections(unsigned long start_pfn)
+{
+ unsigned long start_nr = pfn_to_section_nr(start_pfn);
+
+ if (online_section_nr(start_nr))
+ return 0;
+
+ while (++start_nr <= __highest_present_section_nr) {
+ if (online_section_nr(start_nr))
+ return section_nr_to_pfn(start_nr);
+ }
+
+ return 0;
+}
+#else
+static unsigned long skip_offline_sections(unsigned long start_pfn)
+{
+ return 0;
+}
+#endif
+
/*
* Compound pages of >= pageblock_order should consistently be skipped until
* released. It is always pointless to compact pages of such order (if they are
@@ -1991,8 +2018,14 @@ static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
page = pageblock_pfn_to_page(block_start_pfn,
block_end_pfn, cc->zone);
- if (!page)
+ if (!page) {
+ unsigned long next_pfn;
+
+ next_pfn = skip_offline_sections(block_start_pfn);
+ if (next_pfn)
+ block_end_pfn = next_pfn;
continue;
+ }
/*
* If isolation recently failed, do not retry. Only check the
--
2.27.0
