From: Bart Van Assche bvanassche@acm.org
commit 2112f5c1330a671fa852051d85cb9eadc05d7eb7 upstream.
We noticed that the user interface of Android devices becomes very slow under memory pressure. This is because Android uses the zram driver on top of the loop driver for swapping, because under memory pressure the swap code alternates reads and writes quickly, because mq-deadline is the default scheduler for loop devices and because mq-deadline delays writes by five seconds for such a workload with default settings. Fix this by making the kernel select I/O scheduler 'none' from inside add_disk() for loop devices. This default can be overridden at any time from user space, e.g. via a udev rule. This approach has an advantage compared to changing the I/O scheduler from userspace from 'mq-deadline' into 'none', namely that synchronize_rcu() does not get called.
This patch changes the default I/O scheduler for loop devices from 'mq-deadline' into 'none'.
Additionally, this patch reduces the Android boot time on my test setup with 0.5 seconds compared to configuring the loop I/O scheduler from user space.
Cc: Christoph Hellwig hch@lst.de Cc: Ming Lei ming.lei@redhat.com Cc: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Cc: Martijn Coenen maco@android.com Cc: Jaegeuk Kim jaegeuk@kernel.org Signed-off-by: Bart Van Assche bvanassche@acm.org Link: https://lore.kernel.org/r/20210805174200.3250718-3-bvanassche@acm.org Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/block/loop.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1846,7 +1846,8 @@ static int loop_add(struct loop_device * lo->tag_set.queue_depth = 128; lo->tag_set.numa_node = NUMA_NO_NODE; lo->tag_set.cmd_size = sizeof(struct loop_cmd); - lo->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE; + lo->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE | + BLK_MQ_F_NO_SCHED; lo->tag_set.driver_data = lo;
err = blk_mq_alloc_tag_set(&lo->tag_set);