On Fri, Apr 17, 2015 at 12:06 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > On Fri, Apr 17, 2015 at 10:22:24AM +0800, xuw2015@xxxxxxxxx wrote: >> From: George Wang <xuw2015@xxxxxxxxx> >> >> Function percpu_counter_read just return the current counter, regardless of >> every cpu's count. This counter can be negative value, which will cause the >> checking of "allocated inode counts <= m_maxicount" false positive. > > Have you actually seen this, or is it just theoretical? I produced it by running unionmount-testsuites for overlay, based xfs as upper and lowerdir. I think I can extract the procedure to reproduce it. >> Commit 501ab3238753 "xfs: use generic percpu counters for inode counter <snip> > The correct fix is to use percpu_counter_read_positive(), because in > the majority of cases args.mp->m_maxicount is orders of magnitude > larger (20 million inodes per 100GB of fs space for small filesystems) > than the unaggregated per-cpu counts can cause the sum to go > negative. Hence if it is negative, it may as well be zero because it > makes no difference to the default threshold configurations. Thanks for the explanation, and I agree that totally. Besides, shall we use the exact count in xfs_fs_counts? Because it's a ioctl function, not so much sensitive performance. _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
