Re: [PATCH v2] mm: Introduce dedicated WQ_MEM_RECLAIM workqueue to do lru_add_drain_all

[Tejun Heo <tj@kernel.org>]

On Fri, Jun 03, 2016 at 09:32:01AM +0800, Wang Sheng-Hui wrote:
> 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@foxmail.com>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun

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