Re: [PATCH] mm: compaction: skip memory hole rapidly when isolating migratable pages
From: David Hildenbrand
Date: Mon Jun 12 2023 - 06:15:49 EST
On 12.06.23 11:36, Baolin Wang wrote:
On 6/12/2023 2:39 PM, Huang, Ying wrote:
Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> writes:
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]
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
include/linux/mmzone.h | 10 ++++++++++
mm/compaction.c | 23 ++++++++++++++++++++++-
2 files changed, 32 insertions(+), 1 deletion(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 5a7ada0413da..87e6c535d895 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -2000,6 +2000,16 @@ static inline unsigned long next_present_section_nr(unsigned long section_nr)
return -1;
}
+static inline unsigned long next_online_section_nr(unsigned long section_nr)
+{
+ while (++section_nr <= __highest_present_section_nr) {
+ if (online_section_nr(section_nr))
+ return section_nr;
+ }
+
+ return -1UL;
+}
+
/*
* These are _only_ used during initialisation, therefore they
* can use __initdata ... They could have names to indicate
diff --git a/mm/compaction.c b/mm/compaction.c
index 3398ef3a55fe..3a55fdd20c49 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -229,6 +229,21 @@ static void reset_cached_positions(struct zone *zone)
pageblock_start_pfn(zone_end_pfn(zone) - 1);
}
+static unsigned long skip_hole_pageblock(unsigned long start_pfn)
+{
+ unsigned long next_online_nr;
+ unsigned long start_nr = pfn_to_section_nr(start_pfn);
+
+ if (online_section_nr(start_nr))
+ return -1UL;
Define a macro for the maigic "-1UL"? Which is used for multiple times
in the patch.
I am struggling to find a readable macro for these '-1UL', since the
'-1UL' in next_online_section_nr() indicates that it can not find an
online section. However the '-1' in skip_hole_pageblock() indicates that
it can not find an online pfn.
Maybe something like
#define SECTION_NR_INVALID -1UL
So after more thinking, I will change to return 'NR_MEM_SECTIONS' if can
not find next online section in next_online_section_nr(). And in
skip_hole_pageblock(), I will change to return 0 if can not find next
online pfn. What do you think?
Well, 0 "might be" (and most likely is) a valid section number, so you'd
simulate some kind-of a wraparound. I guess I'd prefer
SECTION_NR_INVALID instead.
--
Cheers,
David / dhildenb