On Wed, Aug 14, 2019 at 1:34 PM Ming Lei <ming.lei@xxxxxxxxxx> wrote: > Another candidate is to not switch to q_usage_counter's percpu mode > until loop becomes Lo_bound, and this way may be more clean. I was thinking about this more; our current sequence is: 1) LOOP_SET_FD 2) LOOP_SET_STATUS64 // for lo_offset/lo_sizelimit 3) LOOP_SET_BLOCK_SIZE // to make sure block size is correct for DIO 4) LOOP_SET_DIRECT_IO // to enable DIO I noticed that LOOP_SET_FD already tries to configure DIO if the underlying file is opened with O_DIRECT; but in this case, it will still fail, because the logical block size of the loop queue must exceed the logical I/O size of the backing device. But the default logical block size of mq is 512. One idea to fix is to call blk_queue_logical_block_size() as part of LOOP_SET_FD, to match the block size of the backing fs in case the backing file is opened with O_DIRECT; you could argue that if the backing file is opened with O_DIRECT, this is what the user wanted anyway. This would allow us to get rid of the latter two ioctl's and already save quite some time. Thanks, Martijn > > Something like the following patch: > > diff --git a/drivers/block/loop.c b/drivers/block/loop.c > index a7461f482467..8791f9242583 100644 > --- a/drivers/block/loop.c > +++ b/drivers/block/loop.c > @@ -1015,6 +1015,9 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, > */ > bdgrab(bdev); > mutex_unlock(&loop_ctl_mutex); > + > + percpu_ref_switch_to_percpu(&lo->lo_queue->q_usage_counter); > + > if (partscan) > loop_reread_partitions(lo, bdev); > if (claimed_bdev) > @@ -1171,6 +1174,8 @@ static int __loop_clr_fd(struct loop_device *lo, bool release) > lo->lo_state = Lo_unbound; > mutex_unlock(&loop_ctl_mutex); > > + percpu_ref_switch_to_atomic(&lo->lo_queue->q_usage_counter, NULL); > + > /* > * Need not hold loop_ctl_mutex to fput backing file. > * Calling fput holding loop_ctl_mutex triggers a circular > @@ -2003,6 +2008,12 @@ static int loop_add(struct loop_device **l, int i) > } > lo->lo_queue->queuedata = lo; > > + /* > + * cheat block layer for not switching to q_usage_counter's > + * percpu mode before loop becomes Lo_bound > + */ > + blk_queue_flag_set(QUEUE_FLAG_INIT_DONE, lo->lo_queue); > + > blk_queue_max_hw_sectors(lo->lo_queue, BLK_DEF_MAX_SECTORS); > > /* > > > thanks, > Ming
