The patch titled
Subject: mm, compaction: shrink compact_control
has been added to the -mm tree. Its filename is
mm-compaction-shrink-compact_control.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-compaction-shrink-compact_control.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-compaction-shrink-compact_control.patch
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From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Subject: mm, compaction: shrink compact_control
Patch series "Increase success rates and reduce latency of compaction", v2.
This series reduces scan rates and success rates of compaction, primarily
by using the free lists to shorten scans, better controlling of skip
information and whether multiple scanners can target the same block and
capturing pageblocks before being stolen by parallel requests. The series
is based on the 4.21/5.0 merge window after Andrew's tree had been merged.
It's known to rebase cleanly.
Primarily I'm using thpscale to measure the impact of the series. The
benchmark creates a large file, maps it, faults it, punches holes in the
mapping so that the virtual address space is fragmented and then tries
to allocate THP. It re-executes for different numbers of threads. From a
fragmentation perspective, the workload is relatively benign but it does
stress compaction.
The overall impact on latencies for a 1-socket machine is
baseline patches
Amean fault-both-3 5362.80 ( 0.00%) 4446.89 * 17.08%*
Amean fault-both-5 9488.75 ( 0.00%) 5660.86 * 40.34%*
Amean fault-both-7 11909.86 ( 0.00%) 8549.63 * 28.21%*
Amean fault-both-12 16185.09 ( 0.00%) 11508.36 * 28.90%*
Amean fault-both-18 12057.72 ( 0.00%) 19013.48 * -57.69%*
Amean fault-both-24 23939.95 ( 0.00%) 19676.16 * 17.81%*
Amean fault-both-30 26606.14 ( 0.00%) 27363.23 ( -2.85%)
Amean fault-both-32 31677.12 ( 0.00%) 23154.09 * 26.91%*
While there is a glitch at the 18-thread mark, it's known that the base
page allocation latency was much lower and huge pages were taking
longer -- partially due a high allocation success rate.
The allocation success rates are much improved
baseline patches
Percentage huge-3 70.93 ( 0.00%) 98.30 ( 38.60%)
Percentage huge-5 56.02 ( 0.00%) 83.36 ( 48.81%)
Percentage huge-7 60.98 ( 0.00%) 89.04 ( 46.01%)
Percentage huge-12 73.02 ( 0.00%) 94.36 ( 29.23%)
Percentage huge-18 94.37 ( 0.00%) 95.87 ( 1.58%)
Percentage huge-24 84.95 ( 0.00%) 97.41 ( 14.67%)
Percentage huge-30 83.63 ( 0.00%) 96.69 ( 15.62%)
Percentage huge-32 81.69 ( 0.00%) 96.10 ( 17.65%)
That's a nearly perfect allocation success rate.
The biggest impact is on the scan rates
Compaction migrate scanned 106520811 26934599
Compaction free scanned 4180735040 26584944
The number of pages scanned for migration was reduced by 74% and the
free scanner was reduced by 99.36%. So much less work in exchange
for lower latency and better success rates.
The series was also evaluated using a workload that heavily fragments
memory but the benefits there are also significant, albeit not presented.
It was commented that we should be rethinking scanning entirely and to
a large extent I agree. However, to achieve that you need a lot of this
series in place first so it's best to make the linear scanners as best
as possible before ripping them out.
This patch (of 25):
The isolate and migrate scanners should never isolate more than a
pageblock of pages so unsigned int is sufficient saving 8 bytes on a
64-bit build.
Link: http://lkml.kernel.org/r/20190104125011.16071-2-mgorman@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Cc: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/mm/internal.h~mm-compaction-shrink-compact_control
+++ a/mm/internal.h
@@ -185,8 +185,8 @@ struct compact_control {
struct list_head freepages; /* List of free pages to migrate to */
struct list_head migratepages; /* List of pages being migrated */
struct zone *zone;
- unsigned long nr_freepages; /* Number of isolated free pages */
- unsigned long nr_migratepages; /* Number of pages to migrate */
+ unsigned int nr_freepages; /* Number of isolated free pages */
+ unsigned int nr_migratepages; /* Number of pages to migrate */
unsigned long total_migrate_scanned;
unsigned long total_free_scanned;
unsigned long free_pfn; /* isolate_freepages search base */
_
Patches currently in -mm which might be from mgorman@xxxxxxxxxxxxxxxxxxx are
mm-page_alloc-do-not-wake-kswapd-with-zone-lock-held.patch
mm-compaction-shrink-compact_control.patch
mm-compaction-rearrange-compact_control.patch
mm-compaction-remove-last_migrated_pfn-from-compact_control.patch
mm-compaction-remove-unnecessary-zone-parameter-in-some-instances.patch
mm-compaction-rename-map_pages-to-split_map_pages.patch
mm-compaction-skip-pageblocks-with-reserved-pages.patch
mm-migrate-immediately-fail-migration-of-a-page-with-no-migration-handler.patch
mm-compaction-always-finish-scanning-of-a-full-pageblock.patch
mm-compaction-use-the-page-allocator-bulk-free-helper-for-lists-of-pages.patch
mm-compaction-ignore-the-fragmentation-avoidance-boost-for-isolation-and-compaction.patch
mm-compaction-use-free-lists-to-quickly-locate-a-migration-source.patch
mm-compaction-keep-migration-source-private-to-a-single-compaction-instance.patch
mm-compaction-use-free-lists-to-quickly-locate-a-migration-target.patch
mm-compaction-avoid-rescanning-the-same-pageblock-multiple-times.patch
mm-compaction-finish-pageblock-scanning-on-contention.patch
mm-compaction-check-early-for-huge-pages-encountered-by-the-migration-scanner.patch
mm-compaction-keep-cached-migration-pfns-synced-for-unusable-pageblocks.patch
mm-compaction-rework-compact_should_abort-as-compact_check_resched.patch
mm-compaction-do-not-consider-a-need-to-reschedule-as-contention.patch
mm-compaction-reduce-unnecessary-skipping-of-migration-target-scanner.patch
mm-compaction-round-robin-the-order-while-searching-the-free-lists-for-a-target.patch
mm-compaction-sample-pageblocks-for-free-pages.patch
mm-compaction-be-selective-about-what-pageblocks-to-clear-skip-hints.patch
mm-compaction-capture-a-page-under-direct-compaction.patch
mm-compaction-do-not-direct-compact-remote-memory.patch
