On Mon, 2017-05-01 at 16:42 +0000, Verma, Vishal L wrote: > On Mon, 2017-05-01 at 09:38 -0700, Dan Williams wrote: > > On Mon, May 1, 2017 at 9:20 AM, Kani, Toshimitsu > > <toshi.k...@hpe.com> : > > > > > > > > Hi Dan, > > > > > > > > > > > > > > > > I was testing the change with CONFIG_DEBUG_ATOMIC_SLEEP > > > > > > > > set this time, and hit the following BUG with > > > > > > > > BTT. This is a separate issue (not introduced by this > > > > > > > > patch), but it shows that we have an issue with the DSM > > > > > > > > call path as well. > > > > > > > > > > > > > > Ah, great find, thanks! We don't see this in the unit > > > > > > > tests because the nfit_test infrastructure takes no > > > > > > > sleeping actions in its simulated DSM path. Outside of > > > > > > > converting btt to use sleeping locks I'm not sure I see a > > > > > > > path forward. I wonder how bad the performance impact of > > > > > > > that would be? Perhaps with opportunistic spinning it > > > > > > > won't be so bad, but I don't see another choice. > > > > > > > > > > > > It's worse than that. Part of the performance optimization > > > > > > of BTT I/O was to avoid locking altogether when we could > > > > > > rely on a BTT lane percpu, so that would also need to be > > > > > > removed. > > > > > > > > > > I do not have a good idea either, but I'd rather disable this > > > > > clearing in the regular BTT write path than adding sleeping > > > > > locks to BTT. Clearing a bad block in the BTT write path is > > > > > difficult/challenging since it allocates a new block. > > > > > > > > Actually, that may make things easier. Can we teach BTT to > > > > track error blocks and clear them before they are reassigned? > > > > > > I was thinking the same after sending it. I think we should be > > > able to do that. > > > > Ok, but we obviously can't develop something that detailed while > > the merge window is open, so I think that means we need to revert > > commit e88da7998d7d "Revert 'libnvdimm: band aid btt vs clear > > poison locking'" and leave BTT I/O-error-clearing disabled for this > > cycle and try again for 4.13. > > Agreed, I'll work on something to track badblocks and clear them > outside the IO path.
Great! Thanks Vishal! -Toshi
