On Fri, Aug 15, 2014 at 10:35:58AM -0400, Brian Foster wrote: > On Fri, Aug 15, 2014 at 04:39:06PM +1000, Dave Chinner wrote: > > From: Dave Chinner <dchinner@xxxxxxxxxx> > > > > There is a lot of cookie-cutter code that looks like: > > > > if (shutdown) > > handle buffer error > > xfs_buf_iorequest(bp) > > error = xfs_buf_iowait(bp) > > if (error) > > handle buffer error > > > > spread through XFS. There's significant complexity now in > > xfs_buf_iorequest() to specifically handle this sort of synchronous > > IO pattern, but there's all sorts of nasty surprises in different > > error handling code dependent on who owns the buffer references and > > the locks. > > > > Pull this pattern into a single helper, where we can hide all the > > synchronous IO warts and hence make the error handling for all the > > callers much saner. This removes the need for a special extra > > reference to protect IO completion processing, as we can now hold a > > single reference across dispatch and waiting, simplifying the sync > > IO smeantics and error handling. > > > > In doing this, also rename xfs_buf_iorequest to xfs_buf_submit and > > make it explicitly handle on asynchronous IO. This forces all users > > to be switched specifically to one interface or the other and > > removes any ambiguity between how the interfaces are to be used. It > > also means that xfs_buf_iowait() goes away. > > > > For the special case of delwri buffer submission and waiting, we > > don't need to issue IO synchronously at all. The second pass to cal > > xfs_buf_iowait() can now just block on xfs_buf_lock() - the buffer > > will be unlocked when the async IO is complete. This formalises a > > sane the method of waiting for async IO - take an extra reference, > > submit the IO, call xfs_buf_lock() when you want to wait for IO > > completion. i.e.: > > > > bp = xfs_buf_find(); > > xfs_buf_hold(bp); > > bp->b_flags |= XBF_ASYNC; > > xfs_buf_iosubmit(bp); > > xfs_buf_lock(bp) > > error = bp->b_error; > > .... > > xfs_buf_relse(bp); > > > > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx> > > --- > > On a quick look at submit_wait this looks pretty good. It actually > implements the general model I've been looking for for sync I/O. E.g., > send the I/O, wait on synchronization, then check for errors. In other > words, a pure synchronous mechanism. The refactoring and new helpers and > whatnot are additional bonus and abstract it nicely. > > I still have to take a closer look to review the actual code, but since > we go and remove the additional sync I/O reference counting business, > why do we even add that stuff early on? Can't we get from where the > current code is to here in a more direct manner? Simply because we need a fix that we can backport, and that fix is a simple addition that does not significantly affect the rest of the patchset... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
