Hi.
While running some memory intensive load, system response
deteriorated just after swap-out started.
The cause of this problem is that when a PG_reclaim page is
moved to the tail of the inactive LRU list in rotate_reclaimable_page(),
lru_lock spin lock is acquired every page writeback . This deteriorates
system performance and makes interrupt hold off time longer when
swap-out started.
Following patch solves this problem. I use pagevec in rotating reclaimable
pages to mitigate LRU spin lock contention and reduce interrupt
hold off time.
I did a test that allocating and touching pages in multiple processes, and
pinging to the test machine in flooding mode to measure response under
memory intensive load.
The test result is:
-2.6.23-rc5
--- testmachine ping statistics ---
3000 packets transmitted, 3000 received, 0% packet loss, time 53222ms
rtt min/avg/max/mdev = 0.074/0.652/172.228/7.176 ms, pipe 11, ipg/ewma
17.746/0.092 ms
-2.6.23-rc5-patched
--- testmachine ping statistics ---
3000 packets transmitted, 3000 received, 0% packet loss, time 51924ms
rtt min/avg/max/mdev = 0.072/0.108/3.884/0.114 ms, pipe 2, ipg/ewma
17.314/0.091 ms
Max round-trip-time was improved.
The test machine spec is that 4CPU(3.16GHz, Hyper-threading enabled)
8GB memory , 8GB swap.
Thanks.
Signed-off-by :Hisashi Hifumi <[email protected]>
diff -Nrup linux-2.6.23-rc5.org/include/linux/swap.h
linux-2.6.23-rc5/include/linux/swap.h
--- linux-2.6.23-rc5.org/include/linux/swap.h 2007-09-06 18:44:06.000000000 +0900
+++ linux-2.6.23-rc5/include/linux/swap.h 2007-09-06 18:45:28.000000000 +0900
@@ -185,6 +185,7 @@ extern void FASTCALL(mark_page_accessed(
extern void lru_add_drain(void);
extern int lru_add_drain_all(void);
extern int rotate_reclaimable_page(struct page *page);
+extern void move_tail_pages(void);
extern void swap_setup(void);
/* linux/mm/vmscan.c */
diff -Nrup linux-2.6.23-rc5.org/mm/swap.c linux-2.6.23-rc5/mm/swap.c
--- linux-2.6.23-rc5.org/mm/swap.c 2007-07-09 08:32:17.000000000 +0900
+++ linux-2.6.23-rc5/mm/swap.c 2007-09-06 18:45:28.000000000 +0900
@@ -93,25 +93,56 @@ void put_pages_list(struct list_head *pa
}
EXPORT_SYMBOL(put_pages_list);
+static void pagevec_move_tail(struct pagevec *pvec)
+{
+ int i;
+ struct zone *zone = NULL;
+ unsigned long flags = 0;
+
+ for (i = 0; i < pagevec_count(pvec); i++) {
+ struct page *page = pvec->pages[i];
+ struct zone *pagezone = page_zone(page);
+
+ if (!PageLRU(page) || !page_count(page))
+ continue;
+
+ if (pagezone != zone) {
+ if (zone)
+ spin_unlock_irqrestore(&zone->lru_lock, flags);
+ zone = pagezone;
+ spin_lock_irqsave(&zone->lru_lock, flags);
+ }
+ if (PageLRU(page) && !PageActive(page) && page_count(page)) {
+ list_move_tail(&page->lru, &zone->inactive_list);
+ __count_vm_event(PGROTATED);
+ }
+ }
+ if (zone)
+ spin_unlock_irqrestore(&zone->lru_lock, flags);
+ pagevec_reinit(pvec);
+}
+
+static DEFINE_PER_CPU(struct pagevec, rotate_pvecs) = { 0, };
+
+void move_tail_pages()
+{
+ struct pagevec *pvec = &per_cpu(rotate_pvecs, get_cpu());
+
+ if (pagevec_count(pvec))
+ pagevec_move_tail(pvec);
+ put_cpu();
+}
+
/*
* Writeback is about to end against a page which has been marked for immediate
* reclaim. If it still appears to be reclaimable, move it to the tail of the
- * inactive list. The page still has PageWriteback set, which will pin it.
- *
- * We don't expect many pages to come through here, so don't bother batching
- * things up.
- *
- * To avoid placing the page at the tail of the LRU while PG_writeback is still
- * set, this function will clear PG_writeback before performing the page
- * motion. Do that inside the lru lock because once PG_writeback is cleared
- * we may not touch the page.
+ * inactive list.
*
* Returns zero if it cleared PG_writeback.
*/
int rotate_reclaimable_page(struct page *page)
{
- struct zone *zone;
- unsigned long flags;
+ struct pagevec *pvec;
if (PageLocked(page))
return 1;
@@ -122,15 +153,16 @@ int rotate_reclaimable_page(struct page
if (!PageLRU(page))
return 1;
- zone = page_zone(page);
- spin_lock_irqsave(&zone->lru_lock, flags);
- if (PageLRU(page) && !PageActive(page)) {
- list_move_tail(&page->lru, &zone->inactive_list);
- __count_vm_event(PGROTATED);
- }
if (!test_clear_page_writeback(page))
BUG();
- spin_unlock_irqrestore(&zone->lru_lock, flags);
+
+ if (PageLRU(page) && !PageActive(page) && page_count(page)) {
+ pvec = &get_cpu_var(rotate_pvecs);
+ if (!pagevec_add(pvec, page))
+ pagevec_move_tail(pvec);
+ put_cpu_var(rotate_pvecs);
+ }
+
return 0;
}
@@ -315,6 +347,7 @@ void release_pages(struct page **pages,
*/
void __pagevec_release(struct pagevec *pvec)
{
+ move_tail_pages();
lru_add_drain();
release_pages(pvec->pages, pagevec_count(pvec), pvec->cold);
pagevec_reinit(pvec);
diff -Nrup linux-2.6.23-rc5.org/mm/vmscan.c linux-2.6.23-rc5/mm/vmscan.c
--- linux-2.6.23-rc5.org/mm/vmscan.c 2007-09-06 18:44:06.000000000 +0900
+++ linux-2.6.23-rc5/mm/vmscan.c 2007-09-06 18:45:28.000000000 +0900
@@ -792,6 +792,7 @@ static unsigned long shrink_inactive_lis
pagevec_init(&pvec, 1);
+ move_tail_pages();
lru_add_drain();
spin_lock_irq(&zone->lru_lock);
do {
-
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