This patch is based on https://patchwork.ozlabs.org/patch/574623/. Tejun submitted commit 23d11a58a9a6 ("workqueue: skip flush dependency checks for legacy workqueues") for the legacy create*_workqueue() interface. But some workq created by alloc_workqueue still reports warning on memory reclaim, e.g nvme_workq with flag WQ_MEM_RECLAIM set: [ 0.153902] workqueue: WQ_MEM_RECLAIM nvme:nvme_reset_work is flushing !WQ_MEM_RECLAIM events:lru_add_drain_per_cpu [ 0.153907] ------------[ cut here ]------------ [ 0.153912] WARNING: CPU: 0 PID: 6 at SoC/linux/kernel/workqueue.c:2448 check_flush_dependency+0xb4/0x10c ... [ 0.154083] [<fffffc00080d6de0>] check_flush_dependency+0xb4/0x10c [ 0.154088] [<fffffc00080d8e80>] flush_work+0x54/0x140 [ 0.154092] [<fffffc0008166a0c>] lru_add_drain_all+0x138/0x188 [ 0.154097] [<fffffc00081ab2dc>] migrate_prep+0xc/0x18 [ 0.154101] [<fffffc0008160e88>] alloc_contig_range+0xf4/0x350 [ 0.154105] [<fffffc00081bcef8>] cma_alloc+0xec/0x1e4 [ 0.154110] [<fffffc0008446ad0>] dma_alloc_from_contiguous+0x38/0x40 [ 0.154114] [<fffffc00080a093c>] __dma_alloc+0x74/0x25c [ 0.154119] [<fffffc00084828d8>] nvme_alloc_queue+0xcc/0x36c [ 0.154123] [<fffffc0008484b2c>] nvme_reset_work+0x5c4/0xda8 [ 0.154128] [<fffffc00080d9528>] process_one_work+0x128/0x2ec [ 0.154132] [<fffffc00080d9744>] worker_thread+0x58/0x434 [ 0.154136] [<fffffc00080df0ec>] kthread+0xd4/0xe8 [ 0.154141] [<fffffc0008093ac0>] ret_from_fork+0x10/0x50 That's because lru_add_drain_all() will schedule the drain work on system_wq, whose flag is set to 0, !WQ_MEM_RECLAIM. Introduce a dedicated WQ_MEM_RECLAIM workqueue to do lru_add_drain_all(), aiding in getting memory freed. Compared with v1: * The key flag is WQ_MEM_RECLAIM. Drop the flag WQ_UNBOUND. * Reserve the warn in lru_init as init code during bootup ignore return code from early_initcall functions. * Instead of falling back to system_wq, crash directly if the wq is used in lru_add_drain_all but was not created in lru_init at init stage. Signed-off-by: Wang Sheng-Hui <shhuiw@xxxxxxxxxxx> --- mm/swap.c | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) diff --git a/mm/swap.c b/mm/swap.c index 9591614..59f5faf 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -667,6 +667,24 @@ static void lru_add_drain_per_cpu(struct work_struct *dummy) static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work); +/* + * lru_add_drain_wq is used to do lru_add_drain_all() from a WQ_MEM_RECLAIM + * workqueue, aiding in getting memory freed. + */ +static struct workqueue_struct *lru_add_drain_wq; + +static int __init lru_init(void) +{ + lru_add_drain_wq = alloc_workqueue("lru-add-drain", WQ_MEM_RECLAIM, 0); + + if (WARN(!lru_add_drain_wq, + "Failed to create workqueue lru_add_drain_wq")) + return -ENOMEM; + + return 0; +} +early_initcall(lru_init); + void lru_add_drain_all(void) { static DEFINE_MUTEX(lock); @@ -686,7 +704,7 @@ void lru_add_drain_all(void) pagevec_count(&per_cpu(lru_deactivate_pvecs, cpu)) || need_activate_page_drain(cpu)) { INIT_WORK(work, lru_add_drain_per_cpu); - schedule_work_on(cpu, work); + queue_work_on(cpu, lru_add_drain_wq, work); cpumask_set_cpu(cpu, &has_work); } } -- 2.7.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>