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Subject[PATCH v18 27/32] mm/swap.c: optimizing __pagevec_lru_add lru_lock
Date
The current relock logical will change lru_lock when if found a new
lruvec, so if 2 memcgs are reading file or alloc page equally, they
could hold the lru_lock alternately.

This patch will record the needed lru_lock and only hold them once in
above scenario. That could reduce the lock contention.

Suggested-by: Konstantin Khlebnikov <koct9i@gmail.com>
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
---
mm/swap.c | 43 ++++++++++++++++++++++++++++++++++++-------
1 file changed, 36 insertions(+), 7 deletions(-)

diff --git a/mm/swap.c b/mm/swap.c
index 2ac78e8fab71..fe53449fa1b8 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -958,24 +958,53 @@ static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec)
trace_mm_lru_insertion(page, lru);
}

+struct add_lruvecs {
+ struct list_head lists[PAGEVEC_SIZE];
+ struct lruvec *vecs[PAGEVEC_SIZE];
+};
+
/*
* Add the passed pages to the LRU, then drop the caller's refcount
* on them. Reinitialises the caller's pagevec.
*/
void __pagevec_lru_add(struct pagevec *pvec)
{
- int i;
+ int i, j, total;
struct lruvec *lruvec = NULL;
unsigned long flags = 0;
+ struct page *page;
+ struct add_lruvecs lruvecs;
+
+ lruvecs.vecs[0] = NULL;
+ for (i = total = 0; i < pagevec_count(pvec); i++) {
+ page = pvec->pages[i];
+ lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));
+
+ /* Try to find a same lruvec */
+ for (j = 0; j <= total; j++)
+ if (lruvec == lruvecs.vecs[j])
+ break;
+ /* A new lruvec */
+ if (j > total) {
+ INIT_LIST_HEAD(&lruvecs.lists[total]);
+ lruvecs.vecs[total] = lruvec;
+ j = total++;
+ lruvecs.vecs[total] = 0;
+ }

- for (i = 0; i < pagevec_count(pvec); i++) {
- struct page *page = pvec->pages[i];
+ list_add(&page->lru, &lruvecs.lists[j]);
+ }

- lruvec = relock_page_lruvec_irqsave(page, lruvec, &flags);
- __pagevec_lru_add_fn(page, lruvec);
+ for (i = 0; i < total; i++) {
+ spin_lock_irqsave(&lruvecs.vecs[i]->lru_lock, flags);
+ while (!list_empty(&lruvecs.lists[i])) {
+ page = lru_to_page(&lruvecs.lists[i]);
+ list_del(&page->lru);
+ __pagevec_lru_add_fn(page, lruvecs.vecs[i]);
+ }
+ spin_unlock_irqrestore(&lruvecs.vecs[i]->lru_lock, flags);
}
- if (lruvec)
- unlock_page_lruvec_irqrestore(lruvec, flags);
+
release_pages(pvec->pages, pvec->nr);
pagevec_reinit(pvec);
}
--
1.8.3.1
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