mm: introduce dedicated WQ_MEM_RECLAIM workqueue to do lru_add_drain_all

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:

    workqueue: WQ_MEM_RECLAIM nvme:nvme_reset_work is flushing !WQ_MEM_RECLAIM events:lru_add_drain_per_cpu
    ------------[ cut here ]------------
    WARNING: CPU: 0 PID: 6 at SoC/linux/kernel/workqueue.c:2448 check_flush_dependency+0xb4/0x10c
    ...
    check_flush_dependency+0xb4/0x10c
    flush_work+0x54/0x140
    lru_add_drain_all+0x138/0x188
    migrate_prep+0xc/0x18
    alloc_contig_range+0xf4/0x350
    cma_alloc+0xec/0x1e4
    dma_alloc_from_contiguous+0x38/0x40
    __dma_alloc+0x74/0x25c
    nvme_alloc_queue+0xcc/0x36c
    nvme_reset_work+0x5c4/0xda8
    process_one_work+0x128/0x2ec
    worker_thread+0x58/0x434
    kthread+0xd4/0xe8
    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.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Wang Sheng-Hui <[email protected]>
Acked-by: Tejun Heo <[email protected]>
Cc: Keith Busch <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thierry Reding <[email protected]>
Cc: Ingo Molnar <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions