On Thu 19-01-17 11:03:12, Dan Williams wrote: > On Thu, Jan 19, 2017 at 10:59 AM, Vishal Verma <vishal.l.verma@xxxxxxxxx> wrote: > > 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. > > Hmm, that may no longer be true after my changes to push dax flushing > to the driver. I.e. we could have a copy_from_iter() implementation > that attempts to clear errors... I'll get that series out and we can > discuss there. Yeah, that was precisely my point - doing copy_from_iter() that clears errors should be possible... Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
