mm: munlock: remove redundant get_page/put_page pair on the fast path
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@suse.cz>
Reviewed-by: Jörn Engel <joern@logfs.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Michel Lespinasse <walken@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/mlock.c b/mm/mlock.c
index abdc612..19a934d 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -303,8 +303,10 @@
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 {
@@ -336,25 +338,25 @@
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 (page)
- put_page(page);
- }
-
pagevec_reinit(pvec);
}