On Tue, Aug 09, 2011 at 01:43:47PM -0400, Mike Snitzer wrote: > On Tue, Aug 09 2011 at 12:13pm -0400, > Tejun Heo <tj@xxxxxxxxxx> wrote: > > > Hello, > > > > On Tue, Aug 09, 2011 at 11:53:51AM -0400, Jeff Moyer wrote: > > > Tejun Heo <tj@xxxxxxxxxx> writes: > > > > I'm a bit confused. We still need ELEVATOR_INSERT_FLUSH fix for > > > > insertion paths, right? Or is blk_insert_cloned_request() supposed to > > > > used only by request based dm which lives under the elevator? If so, > > > > it would be great to make that explicit in the comment. Maybe just > > > > renaming it to blk_insert_dm_cloned_request() would be better as it > > > > wouldn't be safe for other cases anyway. > > > > > > request-based dm is the only caller at present. I'm not a fan of > > > renaming the function, but I'm more than willing to comment it. > > > > I'm still confused and don't think the patch is correct (you can't > > turn off REQ_FUA without decomposing it to data + post flush). > > > > Going through flush machinery twice is okay and I think is the right > > thing to do. At the upper queue, the request is decomposed to member > > requests. After decomposition, it's either REQ_FLUSH w/o data or data > > request w/ or w/o REQ_FUA. When the decomposed request reaches lower > > queue, the lower queue will then either short-circuit it, execute > > as-is or decompose data w/ REQ_FUA into data + REQ_FLUSH sequence. > > > > AFAICS, the breakages are... > > > > * ELEVATOR_INSERT_FLUSH not used properly from insert paths. > > > > * Short circuit not kicking in for the dm requests. (the above and the > > policy patch should solve this, right?) > > > > * BUG(!rq->bio || ...) in blk_insert_flush(). I think we can lift > > this restriction for empty REQ_FLUSH but also dm can just send down > > requests with empty bio. > > [cc'ing dm-devel] > > All of these issues have come to light because DM was not setting > flush_flags based on the underlying device(s). Now fixed in v3.1-rc1: > ed8b752 dm table: set flush capability based on underlying devices > > Given that commit, and that request-based DM is beneath the elevator, it > seems any additional effort to have DM flushes re-enter the flush > machinary is unnecessary. > > We expect: > 1) flushes to have gone through the flush machinary > 2) no FLUSH/FUA should be entering underlying queues if not supported > > I think it best to just document the expectation that any FLUSH/FUA > request that enters blk_insert_cloned_request() will already match the > queue that the request is being sent to. One way to document it is to > change Jeff's flag striping in to pure BUG_ON()s, e.g.: > > --- > block/blk-core.c | 8 ++++++++ > 1 files changed, 8 insertions(+), 0 deletions(-) > > diff --git a/block/blk-core.c b/block/blk-core.c > index b627558..201bb27 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -1710,6 +1710,14 @@ int blk_insert_cloned_request(struct request_queue *q, struct request *rq) > should_fail_request(&rq->rq_disk->part0, blk_rq_bytes(rq))) > return -EIO; > > + /* > + * All FLUSH/FUA requests are expected to have gone through the > + * flush machinary. If a request's cmd_flags doesn't match the > + * flush_flags of the underlying request_queue it is a bug. > + */ > + BUG_ON((rq->cmd_flags & REQ_FLUSH) && !(q->flush_flags & REQ_FLUSH)); > + BUG_ON((rq->cmd_flags & REQ_FUA) && !(q->flush_flags & REQ_FUA)); > + Actually this makes sense and is simple. :-) Is BUG_ON() too harsh, how about WARN_ONCE() variants? To me system continues to work so warning is probably good enough. Thanks Vivek -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
