On Wed, Apr 03, 2019 at 06:48:55PM +0100, Al Viro wrote: > On Wed, Apr 03, 2019 at 06:19:21PM +0100, Al Viro wrote: > > On Wed, Apr 03, 2019 at 06:08:11PM +0100, Al Viro wrote: > > > > > Oh, *brilliant* > > > > > > Let's do d_invalidate() on random dentries and hope they go away. > > > With convoluted and brittle logics for deciding which ones to > > > spare, which is actually wrong. This will pick mountpoints > > > and tear them out, to start with. > > > > > > NAKed-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > > > > > > And this is a NAK for the entire approach; if it has a positive refcount, > > > LEAVE IT ALONE. Period. Don't play this kind of games, they are wrong. > > > d_invalidate() is not something that can be done to an arbitrary dentry. > > > > PS: "try to evict what can be evicted out of this set" can be done, but > > you want something like > > start with empty list > > go through your array of references > > grab dentry->d_lock > > if dentry->d_lockref.count is not zero > > unlock and continue > > if dentry->d_flags & DCACHE_SHRINK_LIST > > ditto, it's not for us to play with > > if (dentry->d_flags & DCACHE_LRU_LIST) > > d_lru_del(dentry); > > d_shrink_add(dentry, &list); > > unlock > > > > on the collection phase and > > if the list is not empty by the end of that loop > > shrink_dentry_list(&list); > > on the disposal. > > Note, BTW, that your constructor is wrong - all it really needs to do > is spin_lock_init() and setting ->d_lockref.count same as lockref_mark_dead() > does, to match the state of dentries being torn down. Thanks for looking at this Al. > __d_alloc() is not holding ->d_lock, since the object is not visible to > anybody else yet; with your changes it *is* visible. I don't quite understand this comment. How is the object visible? The constructor is only called when allocating a new page to the slab and this is done with interrupts disabled. > However, if the > assignment to ->d_lockref.count in __d_alloc() is guaranteed to be > non-zero to non-zero, the above should be safe. I've done as you suggest and set it to -128 Thanks for schooling me on the VFS stuff. Tobin
