Messages in this thread |  | | | Date | Sun, 12 Sep 2010 16:38:13 +0800 | | From | Tao Ma <> | | Subject | Re: [PATCH 02/41] block/loop: queue ordered mode should be DRAIN_FLUSH |
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Hi Tejun, Just a small qs about this patch.
On 09/03/2010 06:29 PM, Tejun Heo wrote: > loop implements FLUSH using fsync but was incorrectly setting its > ordered mode to DRAIN. Change it to DRAIN_FLUSH. In practice, this > doesn't change anything as loop doesn't make use of the block layer > ordered implementation. According to Documentation/block/barrier.txt, QUEUE_ORDERED_DRAIN Requests are ordered by draining the request queue and cache flushing isn't needed.
Sequence: drain => barrier
QUEUE_ORDERED_DRAIN_FLUSH Requests are ordered by draining the request queue and both pre-barrier and post-barrier cache flushings are needed.
Sequence: drain => preflush => barrier => postflush
And for loop device, it call fsync in barrier request. See do_bio_filebacked in drivers/block/loop.c bool barrier = !!(bio->bi_rw & REQ_HARDBARRIER); struct file *file = lo->lo_backing_file;
if (barrier) { if (unlikely(!file->f_op->fsync)) { ret = -EOPNOTSUPP; goto out; } ret = vfs_fsync(file, 0); if (unlikely(ret)) { ret = -EIO; goto out; } } So actually the sync is done in barrier and no extra flush is needed? Or Do I misread the rules in barrier.txt?
Regards, Tao
> > Signed-off-by: Tejun Heo<tj@kernel.org> > --- > drivers/block/loop.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/drivers/block/loop.c b/drivers/block/loop.c > index f3c636d..c3a4a2e 100644 > --- a/drivers/block/loop.c > +++ b/drivers/block/loop.c > @@ -832,7 +832,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, > lo->lo_queue->unplug_fn = loop_unplug; > > if (!(lo_flags& LO_FLAGS_READ_ONLY)&& file->f_op->fsync) > - blk_queue_ordered(lo->lo_queue, QUEUE_ORDERED_DRAIN); > + blk_queue_ordered(lo->lo_queue, QUEUE_ORDERED_DRAIN_FLUSH); > > set_capacity(lo->lo_disk, size); > bd_set_size(bdev, size<< 9);
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