The patch titled
Subject: mm, compaction: sample pageblocks for free pages
has been added to the -mm tree. Its filename is
mm-compaction-sample-pageblocks-for-free-pages.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-compaction-sample-pageblocks-for-free-pages.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-compaction-sample-pageblocks-for-free-pages.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Subject: mm, compaction: sample pageblocks for free pages
Once fast searching finishes, there is a possibility that the linear
scanner is scanning full blocks found by the fast scanner earlier. This
patch uses an adaptive stride to sample pageblocks for free pages. The
more consecutive full pageblocks encountered, the larger the stride until
a pageblock with free pages is found. The scanners might meet slightly
sooner but it is an acceptable risk given that the search of the free
lists may still encounter the pages and adjust the cached PFN of the free
scanner accordingly.
In terms of latency and success rates, the impact is not obvious but the
free scan rate is reduced by 87% on a 1-socket machine and 92% on a
2-socket machine. It's also the first time in the series where the number
of pages scanned by the migration scanner is greater than the free scanner
due to the increased search efficiency.
Link: http://lkml.kernel.org/r/20190104125011.16071-23-mgorman@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Cc: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/mm/compaction.c~mm-compaction-sample-pageblocks-for-free-pages
+++ a/mm/compaction.c
@@ -441,6 +441,7 @@ static unsigned long isolate_freepages_b
unsigned long *start_pfn,
unsigned long end_pfn,
struct list_head *freelist,
+ unsigned int stride,
bool strict)
{
int nr_scanned = 0, total_isolated = 0;
@@ -450,10 +451,14 @@ static unsigned long isolate_freepages_b
unsigned long blockpfn = *start_pfn;
unsigned int order;
+ /* Strict mode is for isolation, speed is secondary */
+ if (strict)
+ stride = 1;
+
cursor = pfn_to_page(blockpfn);
/* Isolate free pages. */
- for (; blockpfn < end_pfn; blockpfn++, cursor++) {
+ for (; blockpfn < end_pfn; blockpfn += stride, cursor += stride) {
int isolated;
struct page *page = cursor;
@@ -624,7 +629,7 @@ isolate_freepages_range(struct compact_c
break;
isolated = isolate_freepages_block(cc, &isolate_start_pfn,
- block_end_pfn, &freelist, true);
+ block_end_pfn, &freelist, 0, true);
/*
* In strict mode, isolate_freepages_block() returns 0 if
@@ -1139,7 +1144,7 @@ fast_isolate_around(struct compact_contr
/* Scan before */
if (start_pfn != pfn) {
- isolate_freepages_block(cc, &start_pfn, pfn, &cc->freepages, false);
+ isolate_freepages_block(cc, &start_pfn, pfn, &cc->freepages, 1, false);
if (cc->nr_freepages >= cc->nr_migratepages)
return;
}
@@ -1147,7 +1152,7 @@ fast_isolate_around(struct compact_contr
/* Scan after */
start_pfn = pfn + nr_isolated;
if (start_pfn != end_pfn)
- isolate_freepages_block(cc, &start_pfn, end_pfn, &cc->freepages, false);
+ isolate_freepages_block(cc, &start_pfn, end_pfn, &cc->freepages, 1, false);
/* Skip this pageblock in the future as it's full or nearly full */
if (cc->nr_freepages < cc->nr_migratepages)
@@ -1333,7 +1338,9 @@ static void isolate_freepages(struct com
unsigned long isolate_start_pfn; /* exact pfn we start at */
unsigned long block_end_pfn; /* end of current pageblock */
unsigned long low_pfn; /* lowest pfn scanner is able to scan */
+ unsigned long nr_isolated;
struct list_head *freelist = &cc->freepages;
+ unsigned int stride;
/* Try a small search of the free lists for a candidate */
isolate_start_pfn = fast_isolate_freepages(cc);
@@ -1356,6 +1363,7 @@ static void isolate_freepages(struct com
block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
zone_end_pfn(zone));
low_pfn = pageblock_end_pfn(cc->migrate_pfn);
+ stride = cc->mode == MIGRATE_ASYNC ? COMPACT_CLUSTER_MAX : 1;
/*
* Isolate free pages until enough are available to migrate the
@@ -1387,8 +1395,8 @@ static void isolate_freepages(struct com
continue;
/* Found a block suitable for isolating free pages from. */
- isolate_freepages_block(cc, &isolate_start_pfn, block_end_pfn,
- freelist, false);
+ nr_isolated = isolate_freepages_block(cc, &isolate_start_pfn,
+ block_end_pfn, freelist, stride, false);
/* Update the skip hint if the full pageblock was scanned */
if (isolate_start_pfn == block_end_pfn)
@@ -1412,6 +1420,13 @@ static void isolate_freepages(struct com
*/
break;
}
+
+ /* Adjust stride depending on isolation */
+ if (nr_isolated) {
+ stride = 1;
+ continue;
+ }
+ stride = min_t(unsigned int, COMPACT_CLUSTER_MAX, stride << 1);
}
/*
_
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
