On Mon, Dec 01, 2008 at 07:04:55PM +0100, Nick Piggin wrote: > On Mon, Dec 01, 2008 at 05:51:13PM +0000, John Levon wrote: > > On Mon, Dec 01, 2008 at 09:33:43AM +0100, Nick Piggin wrote: > > > > > I then got rid of the d_cookie pointer. This shrinks it to 192 bytes. Rant: > > > why was this ever a good idea? The cookie system should increase its hash > > > size or use a tree or something if lookups are a problem. > > > > Are you saying you've made this change without even testing its > > performance impact? > > For oprofile case (maybe if you are profiling hundreds of vmas and > overflow the 4096 byte hash table), no. That case is uncommon and > must be fixed in the dcookie code (as I said, trivial with changing > data structure). I don't want this pointer in struct dentry > regardless of a possible tiny benefit for oprofile. Don't you even have a differential profile showing the impact of removing d_cookie? This hash table lookup will now happen on *every* userspace sample that's processed. That's, uh, a lot. (By all means make your change, but I don't get how it's OK to regress other code, and provide no evidence at all as to its impact.) john -- 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
