On 11/6/13, 7:57 PM, Dave Chinner wrote: > On Wed, Nov 06, 2013 at 05:01:33PM -0600, Ben Myers wrote: >> On Fri, Nov 01, 2013 at 03:27:15PM +1100, Dave Chinner wrote: >>> Hi folks, >>> >>> The following series follows up the recently committed series of >>> patches for 3.13. The first two patches are the remaining >>> uncommitted patches from the previous series. >>> >>> The next two patches are tracing patches, one for AIL manipulations >>> and the other for AGF and AGI read operations. Both of these were >>> written during recent debugging sessions, and both proved useful so >>> should be added to the menagerie of tracepoints we already have >>> avaialble. >>> >>> The final patch is the increasing of the inode cluster size for v5 >>> filesystems. I'd like to get this into v5 filesystems for 3.13 so we >>> get wider exposure of it ASAP so we have more data available to be >>> able to make informed decisions about how to bring this back to v4 >>> filesystems in a safe and controlled manner. >> >> Applied 3 and 4. I still don't understand why the locking on patch 2 is >> correct. Seems like the readers of i_version hold different locks than we do >> when we log the inode. Maybe Christoph can help me with that. > > Readers don't need to hold a spinlock, and many don't. The spinlock > is only there to prevent concurrent updates from "losing" an update > due to races. All modifications to XFS inodes occur via > transactions, inodes are locked exclusively in transactions and > hence we will never lose i_version updates due to races. Hence we > don't need the spinlock during the update, either. I'm not completely convinced that readers don't need to. What happens when we read in the middle of an update? Especially when a 32-bit box reads the 64-bit value in the middle of an update? NFS is the only reader we care about (right?) I see a several paths to i_version reads in nfs; so far I'm finding locked reads: <2 callers of nfs_refresh_inode_locked> spin_lock(&inode->i_lock); nfs_refresh_inode_locked nfs_update_inode nfs_wcc_update_inode (... && inode->i_version == fattr->pre_change_attr) ... if (inode->i_version != fattr->change_attr) { ... nfs_check_inode_attributes (... && inode->i_version != fattr->change_attr) --- update_changeattr spin_lock(&dir->i_lock); if (!cinfo->atomic || cinfo->before != dir->i_version) --- nfs_post_op_update_inode_force_wcc spin_lock(&inode->i_lock); fattr->pre_change_attr = inode->i_version; --- I haven't audited everything but do you have an example of an unlocked reader (which is relevant to xfs)? -Eric _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs