kswapd: avoid unnecessary rebalance after an unsuccessful balancing (d2ebd0f6) · Commits · 戴 / test

In commit ("mm: vmscan: only read new_classzone_idx from pgdat when reclaiming successfully") , Mel Gorman said kswapd is better to sleep after a unsuccessful balancing if there is tighter reclaim request pending in the balancing. But in the following scenario, kswapd do something that is not matched our expectation. The patch fixes this issue. 1, Read pgdat request A (classzone_idx, order = 3) 2, balance_pgdat() 3, During pgdat, a new pgdat request B (classzone_idx, order = 5) is placed 4, balance_pgdat() returns but failed since returned order = 0 5, pgdat of request A assigned to balance_pgdat(), and do balancing again. While the expectation behavior of kswapd should try to sleep. Signed-off-by:

Alex Shi <alex.shi@intel.com> Reviewed-by:

Tim Chen <tim.c.chen@linux.intel.com> Acked-by:

Mel Gorman <mgorman@suse.de> Tested-by:

Pádraig Brady <P@draigBrady.com> Cc: Rik van Riel <riel@redhat.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

+11 −3

Original line number	Diff line number	Diff line
		@@ -2823,7 +2823,9 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
		static int kswapd(void *p)
		{
		unsigned long order, new_order;
		unsigned balanced_order;
		int classzone_idx, new_classzone_idx;
		int balanced_classzone_idx;
		pg_data_t pgdat = (pg_data_t)p;
		struct task_struct *tsk = current;

		@@ -2854,7 +2856,9 @@ static int kswapd(void *p)
		set_freezable();

		order = new_order = 0;
		balanced_order = 0;
		classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
		balanced_classzone_idx = classzone_idx;
		for ( ; ; ) {
		int ret;

		@@ -2863,7 +2867,8 @@ static int kswapd(void *p)
		* new request of a similar or harder type will succeed soon
		* so consider going to sleep on the basis we reclaimed at
		*/
		if (classzone_idx >= new_classzone_idx && order == new_order) {
		if (balanced_classzone_idx >= new_classzone_idx &&
		balanced_order == new_order) {
		new_order = pgdat->kswapd_max_order;
		new_classzone_idx = pgdat->classzone_idx;
		pgdat->kswapd_max_order = 0;
		@@ -2878,7 +2883,8 @@ static int kswapd(void *p)
		order = new_order;
		classzone_idx = new_classzone_idx;
		} else {
		kswapd_try_to_sleep(pgdat, order, classzone_idx);
		kswapd_try_to_sleep(pgdat, balanced_order,
		balanced_classzone_idx);
		order = pgdat->kswapd_max_order;
		classzone_idx = pgdat->classzone_idx;
		pgdat->kswapd_max_order = 0;
		@@ -2895,7 +2901,9 @@ static int kswapd(void *p)
		*/
		if (!ret) {
		trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
		order = balance_pgdat(pgdat, order, &classzone_idx);
		balanced_classzone_idx = classzone_idx;
		balanced_order = balance_pgdat(pgdat, order,
		&balanced_classzone_idx);
		}
		}
		return 0;

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