[PATCH 1/1] mm/page_alloc: add scheduling point to free_unref_page_list

[wangjianxing <wangjianxing@loongson.cn>]

free a large list of pages maybe cause rcu_sched starved on
non-preemptible kernels

rcu: rcu_sched kthread starved for 5359 jiffies! g454793 f0x0
RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=19
[...]
Call Trace:
  free_unref_page_list+0x19c/0x270
  release_pages+0x3cc/0x498
  tlb_flush_mmu_free+0x44/0x70
  zap_pte_range+0x450/0x738
  unmap_page_range+0x108/0x240
  unmap_vmas+0x74/0xf0
  unmap_region+0xb0/0x120
  do_munmap+0x264/0x438
  vm_munmap+0x58/0xa0
  sys_munmap+0x10/0x20
  syscall_common+0x24/0x38

Signed-off-by: wangjianxing <wangjianxing@loongson.cn>
---
 mm/page_alloc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3589febc6..1b96421c8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3479,6 +3479,9 @@ void free_unref_page_list(struct list_head *list)
 		 */
 		if (++batch_count == SWAP_CLUSTER_MAX) {
 			local_unlock_irqrestore(&pagesets.lock, flags);
+
+			cond_resched();
+
 			batch_count = 0;
 			local_lock_irqsave(&pagesets.lock, flags);
 		}
-- 
2.27.0