On Wed, Aug 12, 2020 at 07:25:48PM +1000, Dave Chinner wrote: > From: Dave Chinner <dchinner@xxxxxxxxxx> > > To move away from using the on disk inode buffers to track and log > unlinked inodes, we need pointers to track them in memory. Because > we have arbitrary remove order from the list, it needs to be a > double linked list. > > We start by noting that inodes are always in memory when they are > active on the unlinked list, and hence we can track these inodes > without needing to take references to the inodes or store them in > the list. We cannot, however, use inode locks to protect the inodes > on the list - the list needs an external lock to serialise all > inserts and removals. We can use the existing AGI buffer lock for > this right now as that already serialises all unlinked list > traversals and modifications. > > Hence we can convert the in-memory unlinked list to a simple > list_head list in the perag. We can use list_empty() to detect an > empty unlinked list, likewise we can detect the end of the list when > the inode next pointer points back to the perag list_head. This > makes insert, remove and traversal. > > The only complication here is log recovery of old filesystems that > have multiple lists. These always remove from the head of the list, > so we can easily construct just enough of the unlinked list for > recovery from any list to work correctly. I'd much prefer not bloating the inode for the relative rate case of inode unlinked while still open. Can't we just allocate a temporary structure with the list_head and inode pointer instead?
