On Sun, Jul 17, 2011 at 04:38:24PM -0700, Linus Torvalds wrote: > On Sun, Jul 17, 2011 at 4:16 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > > > > OR > > > > ?- keep part of the patch from Hugh, treating negative in RCU mode as > > "need to unlazy". > > No, urgh, that's horrible. > > Not being able to do an RCU lookup of negative dentries would be > really sad. There are some loads where a negative dentry is the > *common* case. No. Check the patch, please - what it does is exactly "if RCU lookup in the middle of pathname gave us a negative dentry, check that it's really negative ASAP". Negative on the last component is not affected by that and there we *do* go unlazy immediately anyway. If dentry in the middle of pathname is really negative and not stale, we'll get unlazy_walk() check its ->d_seq and fall through the rest - all the way to failure exit in walk_component(). Yes, we'll bump and drop ->d_count. On that negative dentry in the middle. On the other hand, if that sucker is stale, unlazy_walk() will check ->d_seq and bugger off. And no matter what we do, that pathname resolution is going to have to be done in non-RCU mode at that point and earlier is better. Your variant could only lead to walking deeper into the tree before we discover a stale dentry. Because it *can't* have non-stale descendents anymore. Just more work for us... IOW, once we run into negative dentry in RCU mode in do_lookup(), we really need to drop out of RCU mode ASAP. Note that it's *NOT* about not finding negative dentries in RCU dcache lookups or any such silliness - that, of course, would be dumb. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
