On Wed, Sep 02, 2015 at 01:04:01PM -0600, Ross Zwisler wrote: > On Tue, Sep 01, 2015 at 03:18:41PM +0300, Boaz Harrosh wrote: > > So the approach we took was a bit different to exactly solve these > > problem, and to also not over flush too much. here is what we did. > > > > * At vm_operations_struct we also override the .close vector (say call it dax_vm_close) > > > > * At dax_vm_close() on writable files call ->fsync(,vma->vm_start, vma->vm_end,) > > (We have an inode flag if the file was actually dirtied, but even if not, that will > > not be that bad, so a file was opened for write, mmapped, but actually never > > modified. Not a lot of these, and the do nothing cl_flushing is very fast) > > > > * At ->fsync() do the actual cl_flush for all cases but only iff > > if (mapping_mapped(inode->i_mapping) == 0) > > return 0; > > > > This is because data written not through mmap is already persistent and we > > do not need the cl_flushing > > > > Apps expect all these to work: > > 1. open mmap m-write msync ... close > > 2. open mmap m-write fsync ... close > > 3. open mmap m-write unmap ... fsync close > > > > 4. open mmap m-write sync ... > > So basically you made close have an implicit fsync? What about the flow that > looks like this: > > 5. open mmap close m-write > > This guy definitely needs an msync/fsync at the end to make sure that the > m-write becomes durable. We can sync on pte_dirty() during zap_page_range(): it's practically free, since we page walk anyway. With this approach it probably makes sense to come back to page walk on msync() side too to be consistent wrt pte_dirty() meaning. > Also, the CLOSE(2) man page specifically says that a flush does not occur at > close: > A successful close does not guarantee that the data has been > successfully saved to disk, as the kernel defers writes. It > is not common for a filesystem to flush the buffers when the stream is > closed. If you need to be sure that the data is physically stored, > use fsync(2). (It will depend on the disk hardware at this point.) > > I don't think that adding an implicit fsync to close is the right solution - > we just need to get msync and fsync correctly working. I doesn't mean we can't sync if we can do without noticible performance degradation. -- Kirill A. Shutemov -- 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
