On Wed, Jun 03, 2020 at 10:57:49AM -0400, Brian Foster wrote: > On Wed, Jun 03, 2020 at 07:29:18AM +1000, Dave Chinner wrote: > > On Tue, Jun 02, 2020 at 12:45:35PM -0400, Brian Foster wrote: > > > On Tue, Jun 02, 2020 at 07:42:25AM +1000, Dave Chinner wrote: > > > > From: Dave Chinner <dchinner@xxxxxxxxxx> > > > > > > > > Inode buffers always have write IO callbacks, so by marking them > > > > directly we can avoid needing to attach ->b_iodone functions to > > > > them. This avoids an indirect call, and makes future modifications > > > > much simpler. > > > > > > > > This is largely a rearrangement of the code at this point - no IO > > > > completion functionality changes at this point, just how the > > > > code is run is modified. > > > > > > > > > > Ok, I was initially thinking this patch looked incomplete in that we > > > continue to set ->b_iodone() on inode buffers even though we'd never > > > call it. Looking ahead, I see that the next few patches continue to > > > clean that up to eventually remove ->b_iodone(), so that addresses that. > > > > > > My only other curiosity is that while there may not be any functional > > > difference, this technically changes callback behavior in that we set > > > the new flag in some contexts that don't currently attach anything to > > > the buffer, right? E.g., xfs_trans_inode_alloc_buf() sets the flag on > > > inode chunk init, which means we can write out an inode buffer without > > > any attached/flushed inodes. > > > > Yes, it can happen, and it happens before this patch, too, because > > the AIL can push the buffer log item directly and that does not > > flush dirty inodes to the buffer before it writes back(*). > > > > I was thinking more about cases where there are actually no inodes > attached. > > > As it is, xfs_buf_inode_iodone() on a buffer with no inode attached > > if functionally identical to the existing xfs_buf_iodone() callback > > that would otherwise be done. i.e. it just runs the buffer log item > > completion callback. Hence the change here rearranges code, but it > > does not change behaviour at all. > > > > Right. That's indicative from the code, but doesn't help me understand > why the change is made. That's all I'm asking for... > > > (*) this is a double-write bug that this patch set does not address. > > i.e. buffer log item flushes the buffer without flushing inodes, IO > > compeletes, then inode flush to the buffer and we do another IO to > > clean them. This is addressed by a follow-on patchset that tracks > > dirty inodes via ordered cluster buffers, such that pushing the > > buffer always triggers xfs_iflush_cluster() on buffers tagged > > _XBF_INODES... > > > > Ok, interesting (but seems beyond the scope of this series). It is used in this series in the ail buffer resubmit code to clear the LI_FAILED state appropriately, because inode items are treated differently to dquot items once they track the cluster buffer... > > > Is the intent of that to support future > > > changes? If so, a note about that in the commit log would be helpful. > > > > That's part of it, as you can see from the (*) above. But the commit > > log already says "..., and makes future modifications much simpler." > > Was that insufficient to indicate that it will be used later on? > > > > That's a rather vague hint. ;P I was more hoping for something like: > "While this is largely a refactor of existing functionality, broaden the > scope of the flag to beyond where inodes are explicitly attached because > <some actual reason>. This has the effect of possibly invoking the > callback in cases where it wouldn't have been previously, but this is > not a functional change because the callback is effectively a no-op when > inodes are not attached." Ok. -Dave. -- Dave Chinner david@xxxxxxxxxxxxx
