The performance of the fast path in munlock_vma_range() can be further improved
by avoiding atomic ops of a redundant get_page()/put_page() pair.
When calling get_page() during page isolation, we already have the pin from
follow_page_mask(). This pin will be then returned by __pagevec_lru_add(),
after which we do not reference the pages anymore.
After this patch, an 8% speedup was measured for munlocking a 56GB large memory
area with THP disabled.
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
mm/mlock.c | 26 ++++++++++++++------------
1 file changed, 14 insertions(+), 12 deletions(-)
diff --git a/mm/mlock.c b/mm/mlock.c
index 5c38475..b0e897a 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -297,8 +297,10 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
if (PageLRU(page)) {
lruvec = mem_cgroup_page_lruvec(page, zone);
lru = page_lru(page);
-
- get_page(page);
+ /*
+ * We already have pin from follow_page_mask()
+ * so we can spare the get_page() here.
+ */
ClearPageLRU(page);
del_page_from_lru_list(page, lruvec, lru);
} else {
@@ -332,24 +334,24 @@ skip_munlock:
lock_page(page);
if (!__putback_lru_fast_prepare(page, &pvec_putback,
&pgrescued)) {
- /* Slow path */
+ /*
+ * Slow path. We don't want to lose the last pin
+ * before unlock_page()
+ */
+ get_page(page); /* for putback_lru_page() */
__munlock_isolated_page(page);
unlock_page(page);
+ put_page(page); /* from follow_page_mask() */
}
}
- /* Phase 3: page putback for pages that qualified for the fast path */
+ /*
+ * Phase 3: page putback for pages that qualified for the fast path
+ * This will also call put_page() to return pin from follow_page_mask()
+ */
if (pagevec_count(&pvec_putback))
__putback_lru_fast(&pvec_putback, pgrescued);
- /* Phase 4: put_page to return pin from follow_page_mask() */
- for (i = 0; i < nr; i++) {
- struct page *page = pvec->pages[i];
-
- if (likely(page))
- put_page(page);
- }
-
pagevec_reinit(pvec);
}
--
1.8.1.4
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