This patch makes the comment for cc->wrapped longer, explaining
what is really going on. It also incorporates the comment fix
pointed out by Minchan.
Additionally, Minchan found that, when no pages get isolated,
high_pte could be a value that is much lower than desired,
which might potentially cause compaction to skip a range of
pages.
Only assign zone->compact_cache_free_pfn if we actually
isolated free pages for compaction.
Split out the calculation to get the start of the last page
block in a zone into its own, commented function.
Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
---
include/linux/mmzone.h | 2 +-
mm/compaction.c | 30 ++++++++++++++++++++++--------
mm/internal.h | 6 +++++-
3 files changed, 28 insertions(+), 10 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index e629594..e957fa1 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -370,7 +370,7 @@ struct zone {
spinlock_t lock;
int all_unreclaimable; /* All pages pinned */
#if defined CONFIG_COMPACTION || defined CONFIG_CMA
- /* pfn where the last order > 0 compaction isolated free pages */
+ /* pfn where the last incremental compaction isolated free pages */
unsigned long compact_cached_free_pfn;
#endif
#ifdef CONFIG_MEMORY_HOTPLUG
diff --git a/mm/compaction.c b/mm/compaction.c
index 2668b77..3812c3e 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -472,10 +472,11 @@ static void isolate_freepages(struct zone *zone,
* looking for free pages, the search will restart here as
* page migration may have returned some pages to the allocator
*/
- if (isolated)
+ if (isolated) {
high_pfn = max(high_pfn, pfn);
- if (cc->order > 0)
- zone->compact_cached_free_pfn = high_pfn;
+ if (cc->order > 0)
+ zone->compact_cached_free_pfn = high_pfn;
+ }
}
/* split_free_page does not map the pages */
@@ -569,6 +570,21 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
return ISOLATE_SUCCESS;
}
+/*
+ * Returns the start pfn of the laste page block in a zone.
+ * This is the starting point for full compaction of a zone.
+ * Compaction searches for free pages from the end of each zone,
+ * while isolate_freepages_block scans forward inside each page
+ * block.
+ */
+static unsigned long start_free_pfn(struct zone *zone)
+{
+ unsigned long free_pfn;
+ free_pfn = zone->zone_start_pfn + zone->spanned_pages;
+ free_pfn &= ~(pageblock_nr_pages-1);
+ return free_pfn;
+}
+
static int compact_finished(struct zone *zone,
struct compact_control *cc)
{
@@ -587,10 +603,9 @@ static int compact_finished(struct zone *zone,
if (cc->free_pfn <= cc->migrate_pfn) {
if (cc->order > 0 && !cc->wrapped) {
/* We started partway through; restart at the end. */
- unsigned long free_pfn;
- free_pfn = zone->zone_start_pfn + zone->spanned_pages;
- free_pfn &= ~(pageblock_nr_pages-1);
+ unsigned long free_pfn = start_free_pfn(zone);
zone->compact_cached_free_pfn = free_pfn;
+ cc->free_pfn = free_pfn;
cc->wrapped = 1;
return COMPACT_CONTINUE;
}
@@ -703,8 +718,7 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
cc->start_free_pfn = cc->free_pfn;
} else {
/* Order == -1 starts at the end of the zone. */
- cc->free_pfn = cc->migrate_pfn + zone->spanned_pages;
- cc->free_pfn &= ~(pageblock_nr_pages-1);
+ cc->free_pfn = start_free_pfn(zone);
}
migrate_prep_local();
diff --git a/mm/internal.h b/mm/internal.h
index 0b72461..da6b9b2 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -121,7 +121,11 @@ struct compact_control {
unsigned long start_free_pfn; /* where we started the search */
unsigned long migrate_pfn; /* isolate_migratepages search base */
bool sync; /* Synchronous migration */
- bool wrapped; /* Last round for order>0 compaction */
+ bool wrapped; /* Order > 0 compactions are
+ incremental, once free_pfn
+ and migrate_pfn meet, we restart
+ from the top of the zone;
+ remember we wrapped around. */
int order; /* order a direct compactor needs */
int migratetype; /* MOVABLE, RECLAIMABLE etc */
--
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