Re: [PATCH v2] mm: compaction: skip memory hole rapidly when isolating migratable pages
From: David Hildenbrand
Date: Tue Jun 13 2023 - 08:37:30 EST
On 13.06.23 13:13, Baolin Wang wrote:
On 6/13/2023 5:56 PM, David Hildenbrand wrote:
On 13.06.23 10:55, Baolin Wang wrote:
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>
---
Changes from v1:
- Fix building errors if CONFIG_SPARSEMEM is not selected.
- Use NR_MEM_SECTIONS instead of '-1' per Huang Ying.
---
include/linux/mmzone.h | 10 ++++++++++
mm/compaction.c | 30 +++++++++++++++++++++++++++++-
2 files changed, 39 insertions(+), 1 deletion(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 5a7ada0413da..5ff1fa2efe28 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 NR_MEM_SECTIONS;
+}
+
/*
* 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..c31ff6123891 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -229,6 +229,28 @@ static void reset_cached_positions(struct zone
*zone)
pageblock_start_pfn(zone_end_pfn(zone) - 1);
}
+#ifdef CONFIG_SPARSEMEM
+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 0;
+
+ next_online_nr = next_online_section_nr(start_nr);
+ if (next_online_nr < NR_MEM_SECTIONS)
+ return section_nr_to_pfn(next_online_nr);
+
I would simply inline next_online_section_nr and simplify (and add a
comment):
/*
* 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_hole_pageblock(unsigned long start_pfn)
{
unsigned long nr = pfn_to_section_nr(start_pfn);
if (online_section_nr(nr))
return 0;
while (++nr <= __highest_present_section_nr) {
if (online_section_nr(nr))
return section_nr_to_pfn(nr);
}
return 0
}
Easier, no?
Originally I want to add a common helper like next_present_section_nr(),
which can be used by other users. But yes, your suggestion is easier,
and I am fine with that.
And maybe just call that function "skip_offline_sections()" then?
Because we're not operating on pageblocks.
OK. Thanks.
Feel free to add to the simplified version
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
--
Cheers,
David / dhildenb