On Fri 30-09-16 01:57:14, Christoph Hellwig wrote: > On Tue, Sep 27, 2016 at 06:43:34PM +0200, Jan Kara wrote: > > Currently invalidate_inode_pages2_range() and invalidate_mapping_pages() > > just delete all exceptional radix tree entries they find. For DAX this > > is not desirable as we track cache dirtiness in these entries and when > > they are evicted, we may not flush caches although it is necessary. This > > can for example manifest when we write to the same block both via mmap > > and via write(2) (to different offsets) and fsync(2) then does not > > properly flush CPU caches when modification via write(2) was the last > > one. > > Can you come up with an xfstests test case for these data loss cases? I'm not sure how to easily do this. For DAX to be enabled, we need memory-like storage so there's no easy way to intercept writes that may be only in CPU caches but not in the persistent memory. Eventually we may want to write a DAX flush testing driver - something like ramdisk but that would keep "cached" and "persistent" version of each page and on wb_cache_pmem() copy one version to the other. We'd also need to hook into copy_from_iter_nocache() and stuff to make cache-avoiding writes behave as expected but all in all it should be doable... 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
