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. -- 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
