hi, Al Viro, On Fri, Dec 01, 2023 at 08:04:46PM +0000, Al Viro wrote: > On Fri, Dec 01, 2023 at 06:56:03AM +0000, Al Viro wrote: > > On Fri, Dec 01, 2023 at 04:09:51AM +0000, Al Viro wrote: > > > On Fri, Dec 01, 2023 at 10:13:09AM +0800, Oliver Sang wrote: > > > > > > > > Very interesting... Out of curiosity, what effect would the following > > > > > have on top of 1b738f196e? > > > > > > > > I applied the patch upon 1b738f196e (as below fec356fd0c), but seems less > > > > useful. > > > > > > I would be rather surprised if it fixed anything; it's just that 1b738f196e > > > changes two things - locking rules for __dentry_kill() and, in some cases, > > > the order of dentry eviction in shrink_dentry_list(). That delta on top of > > > it restores the original order in shrink_dentry_list(), leaving pretty much > > > the changes in lock_for_kill()/dput()/__dentry_kill(). > > > > > > Interesting... Looks like there are serious changes in context switch > > > frequencies, but I don't see where could that have come from... > > > > In principle it could be an effect of enforcing the ordering between __dentry_kill() > > of child and parent, but if that's what is going on... we would've seen > > more iterations of loop in shrink_dcache_parent() and/or d_walk() calls in > > it having more work to do. But... had that been what's going on, wouldn't we > > see some of those functions in the changed part of profile? > > > > I'll try to split that thing into a series of steps, so we could at least narrow > > the effect down, but that'll have to wait until tomorrow ;-/ > > OK, a carved-up series (on top of 1b738f196e^) is in #carved-up-__dentry_kill > That's 9 commits, leading to something close to 1b738f196e+patch you've tested > yesterday; could you profile them on your reproducers? That might give some > useful information about the nature of the regression... > we rerun the test and confirmed the regression still exists if comparing 20f7d1936e8a2 (viro-vfs/carved-up-__dentry_kill) step 9: fold decrment of parent's refcount into __dentry_kill() with b4cc0734d2574 d_prune_aliases(): use a shrink list the data is similar to our previous report. now we feed the results into our auto-bisect tool and hope to get results later but due to the limitation such like auto-bisect cannot capture multi commits if they all contribute to the regression, after we get the results from auto bisect, we will check if any further munual efforts needed. Thanks
