[PATCH 1/8] mm, page_alloc: Enable/disable IRQs once when freeing a list of pages

Mel Gorman
2017-10-18T07:59:58Z

Freeing a list of pages current enables/disables IRQs for each page freed.
This patch splits freeing a list of pages into two operations -- preparing
the pages for freeing and the actual freeing. This is a tradeoff - we're
taking two passes of the list to free in exchange for avoiding multiple
enable/disable of IRQs.

sparsetruncate (tiny)
4.14.0-rc4 4.14.0-rc4
janbatch-v1r1 oneirq-v1r1
Min Time 149.00 ( 0.00%) 141.00 ( 5.37%)
1st-qrtle Time 150.00 ( 0.00%) 142.00 ( 5.33%)
2nd-qrtle Time 151.00 ( 0.00%) 142.00 ( 5.96%)
3rd-qrtle Time 151.00 ( 0.00%) 143.00 ( 5.30%)
Max-90% Time 153.00 ( 0.00%) 144.00 ( 5.88%)
Max-95% Time 155.00 ( 0.00%) 147.00 ( 5.16%)
Max-99% Time 201.00 ( 0.00%) 195.00 ( 2.99%)
Max Time 236.00 ( 0.00%) 230.00 ( 2.54%)
Amean Time 152.65 ( 0.00%) 144.37 ( 5.43%)
Stddev Time 9.78 ( 0.00%) 10.44 ( -6.72%)
Coeff Time 6.41 ( 0.00%) 7.23 ( -12.84%)
Best99%Amean Time 152.07 ( 0.00%) 143.72 ( 5.50%)
Best95%Amean Time 150.75 ( 0.00%) 142.37 ( 5.56%)
Best90%Amean Time 150.59 ( 0.00%) 142.19 ( 5.58%)
Best75%Amean Time 150.36 ( 0.00%) 141.92 ( 5.61%)
Best50%Amean Time 150.04 ( 0.00%) 141.69 ( 5.56%)
Best25%Amean Time 149.85 ( 0.00%) 141.38 ( 5.65%)

With a tiny number of files, each file truncated has resident page cache
and it shows that time to truncate is roughtly 5-6% with some minor jitter.

4.14.0-rc4 4.14.0-rc4
janbatch-v1r1 oneirq-v1r1
Hmean SeqCreate ops 65.27 ( 0.00%) 81.86 ( 25.43%)
Hmean SeqCreate read 39.48 ( 0.00%) 47.44 ( 20.16%)
Hmean SeqCreate del 24963.95 ( 0.00%) 26319.99 ( 5.43%)
Hmean RandCreate ops 65.47 ( 0.00%) 82.01 ( 25.26%)
Hmean RandCreate read 42.04 ( 0.00%) 51.75 ( 23.09%)
Hmean RandCreate del 23377.66 ( 0.00%) 23764.79 ( 1.66%)

As expected, there is a small gain for the delete operation.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
mm/page_alloc.c | 58 +++++++++++++++++++++++++++++++++++++++++++--------------
1 file changed, 44 insertions(+), 14 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 77e4d3c5c57b..167e163cf733 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2590,24 +2590,26 @@ void mark_free_pages(struct zone *zone)
}
#endif /* CONFIG_PM */

-/*
- * Free a 0-order page
- * cold == true ? free a cold page : free a hot page
- */
-void free_hot_cold_page(struct page *page, bool cold)
+static bool free_hot_cold_page_prepare(struct page *page, unsigned long pfn)
{
- struct zone *zone = page_zone(page);
- struct per_cpu_pages *pcp;
- unsigned long flags;
- unsigned long pfn = page_to_pfn(page);
int migratetype;

if (!free_pcp_prepare(page))
- return;
+ return false;

migratetype = get_pfnblock_migratetype(page, pfn);
set_pcppage_migratetype(page, migratetype);
- local_irq_save(flags);
+ return true;
+}
+
+static void free_hot_cold_page_commit(struct page *page, unsigned long pfn,
+ bool cold)
+{
+ struct zone *zone = page_zone(page);
+ struct per_cpu_pages *pcp;
+ int migratetype;
+
+ migratetype = get_pcppage_migratetype(page);
__count_vm_event(PGFREE);

/*
@@ -2620,7 +2622,7 @@ void free_hot_cold_page(struct page *page, bool cold)
if (migratetype >= MIGRATE_PCPTYPES) {
if (unlikely(is_migrate_isolate(migratetype))) {
free_one_page(zone, page, pfn, 0, migratetype);
- goto out;
+ return;
}
migratetype = MIGRATE_MOVABLE;
}
@@ -2636,8 +2638,22 @@ void free_hot_cold_page(struct page *page, bool cold)
free_pcppages_bulk(zone, batch, pcp);
pcp->count -= batch;
}
+}

-out:
+/*
+ * Free a 0-order page
+ * cold == true ? free a cold page : free a hot page
+ */
+void free_hot_cold_page(struct page *page, bool cold)
+{
+ unsigned long flags;
+ unsigned long pfn = page_to_pfn(page);
+
+ if (!free_hot_cold_page_prepare(page, pfn))
+ return;
+
+ local_irq_save(flags);
+ free_hot_cold_page_commit(page, pfn, cold);
local_irq_restore(flags);
}

@@ -2647,11 +2663,25 @@ void free_hot_cold_page(struct page *page, bool cold)
void free_hot_cold_page_list(struct list_head *list, bool cold)
{
struct page *page, *next;
+ unsigned long flags, pfn;
+
+ /* Prepare pages for freeing */
+ list_for_each_entry_safe(page, next, list, lru) {
+ pfn = page_to_pfn(page);
+ if (!free_hot_cold_page_prepare(page, pfn))
+ list_del(&page->lru);
+ page->private = pfn;
+ }

+ local_irq_save(flags);
list_for_each_entry_safe(page, next, list, lru) {
+ unsigned long pfn = page->private;
+
+ page->private = 0;
trace_mm_page_free_batched(page, cold);
- free_hot_cold_page(page, cold);
+ free_hot_cold_page_commit(page, pfn, cold);
}
+ local_irq_restore(flags);
}

/*
--
2.14.0