We observed kcompactd hung at __lock_page():
INFO: task kcompactd0:57 blocked for more than 120 seconds.
Not tainted 4.19.56.x86_64 #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kcompactd0 D 0 57 2 0x80000000
Call Trace:
? __schedule+0x236/0x860
schedule+0x28/0x80
io_schedule+0x12/0x40
__lock_page+0xf9/0x120
? page_cache_tree_insert+0xb0/0xb0
? update_pageblock_skip+0xb0/0xb0
migrate_pages+0x88c/0xb90
? isolate_freepages_block+0x3b0/0x3b0
compact_zone+0x5f1/0x870
kcompactd_do_work+0x130/0x2c0
? __switch_to_asm+0x35/0x70
? __switch_to_asm+0x41/0x70
? kcompactd_do_work+0x2c0/0x2c0
? kcompactd+0x73/0x180
kcompactd+0x73/0x180
? finish_wait+0x80/0x80
kthread+0x113/0x130
? kthread_create_worker_on_cpu+0x50/0x50
ret_from_fork+0x35/0x40
which faddr2line maps to:
migrate_pages+0x88c/0xb90:
lock_page at include/linux/pagemap.h:483
(inlined by) __unmap_and_move at mm/migrate.c:1024
(inlined by) unmap_and_move at mm/migrate.c:1189
(inlined by) migrate_pages at mm/migrate.c:1419
Sometimes kcompactd eventually got out of this situation, sometimes not.
I think for memory compaction, it is a best effort to migrate the pages,
so it doesn't have to wait for I/O to complete. It is fine to call
trylock_page() here, which is pretty much similar to
buffer_migrate_lock_buffers().
Given MIGRATE_SYNC_LIGHT is used on compaction path, just relax the
check for it.
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
---
mm/migrate.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/mm/migrate.c b/mm/migrate.c
index 86873b6f38a7..df60026779d2 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1010,7 +1010,8 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
bool is_lru = !__PageMovable(page);
if (!trylock_page(page)) {
- if (!force || mode == MIGRATE_ASYNC)
+ if (!force || mode == MIGRATE_ASYNC
+ || mode == MIGRATE_SYNC_LIGHT)
goto out;
/*
--
2.21.1
