Hi Kent, On Sat, Mar 12, 2016 at 5:24 PM, Kent Overstreet <[email protected]> wrote: > On Sat, Mar 12, 2016 at 04:49:41PM +0800, Ming Lei wrote: >> On Sat, Mar 12, 2016 at 3:43 PM, Kent Overstreet >> <[email protected]> wrote: >> > I don't know exactly how it's broken, but with that patch segment counting >> > is >> > broken - I'm seeing blk_rq_map_sg() overrun the end of the sgtable. >> > >> > I suggest reverting it for 4.5... >> >> Kent, could you share your test case? I'd like to figure out the root cause. > > xfstest 036 on bcachefs.
Given bcachefs isn't merged, could you provide one way to reproduce it with clean upstream kernel? > >> BTW, I don't object to revert it given it is close to v4.5 release, but I am >> curious how it breaks segment couting. > > If you want to debug your version (personally I'd just revert to the simpler > one), I'd start by having your helper use both methods to calculate the last > biovec, and then assert that they're equal. > > Also make sure you're testing with a sub-page sized blocksize, if filesystem > blocksize == page size you're not going to be testing the interesting cases I just run xfstests 036 over bcache and md, with block size 1024/2048, with xfs/ext4/btrfs, looks the segment counting issue can't be reproduced. If the issue can only be reproduced with bcachefs, I suggest we don't revert it until the root cause is figured out. Thanks, Ming Lei
