On 01/19, Jan Kara wrote: > On Wed 18-01-17 21:56:58, Verma, Vishal L wrote: > > On Wed, 2017-01-18 at 13:32 -0800, Dan Williams wrote: > > > On Wed, Jan 18, 2017 at 1:02 PM, Darrick J. Wong > > > <darrick.wong@xxxxxxxxxx> wrote: > > > > On Wed, Jan 18, 2017 at 03:39:17PM -0500, Jeff Moyer wrote: > > > > > Jan Kara <jack@xxxxxxx> writes: > > > > > > > > > > > On Tue 17-01-17 15:14:21, Vishal Verma wrote: > > > > > > > Your note on the online repair does raise another tangentially > > > > > > > related > > > > > > > topic. Currently, if there are badblocks, writes via the bio > > > > > > > submission > > > > > > > path will clear the error (if the hardware is able to remap > > > > > > > the bad > > > > > > > locations). However, if the filesystem is mounted eith DAX, > > > > > > > even > > > > > > > non-mmap operations - read() and write() will go through the > > > > > > > dax paths > > > > > > > (dax_do_io()). We haven't found a good/agreeable way to > > > > > > > perform > > > > > > > error-clearing in this case. So currently, if a dax mounted > > > > > > > filesystem > > > > > > > has badblocks, the only way to clear those badblocks is to > > > > > > > mount it > > > > > > > without DAX, and overwrite/zero the bad locations. This is a > > > > > > > pretty > > > > > > > terrible user experience, and I'm hoping this can be solved in > > > > > > > a better > > > > > > > way. > > > > > > > > > > > > Please remind me, what is the problem with DAX code doing > > > > > > necessary work to > > > > > > clear the error when it gets EIO from memcpy on write? > > > > > > > > > > You won't get an MCE for a store; only loads generate them. > > > > > > > > > > Won't fallocate FL_ZERO_RANGE clear bad blocks when mounted with > > > > > -o dax? > > > > > > > > Not necessarily; XFS usually implements this by punching out the > > > > range > > > > and then reallocating it as unwritten blocks. > > > > > > > > > > That does clear the error because the unwritten blocks are zeroed and > > > errors cleared when they become allocated again. > > > > Yes, the problem was that writes won't clear errors. zeroing through > > either hole-punch, truncate, unlinking the file should all work > > (assuming the hole-punch or truncate ranges wholly contain the > > 'badblock' sector). > > Let me repeat my question: You have mentioned that if we do IO through DAX, > writes won't clear errors and we should fall back to normal block path to > do write to clear the error. What does prevent us from directly clearing > the error from DAX path? > With DAX, all IO goes through DAX paths. There are two cases: 1. mmap and loads/stores: Obviously there is no kernel intervention here, and no badblocks handling is possible. 2. read() or write() IO: In the absence of dax, this would go through the bio submission path, through the pmem driver, and that would handle error clearing. With DAX, this goes through dax_iomap_actor, which also doesn't go through the pmem driver (it does a dax mapping, followed by essentially memcpy), and hence cannot handle badblocks. > Honza > -- > Jan Kara <jack@xxxxxxxx> > SUSE Labs, CR -- 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
