On 09/02/2015 10:04 PM, Ross Zwisler wrote: > On Tue, Sep 01, 2015 at 03:18:41PM +0300, Boaz Harrosh wrote: <> >> 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 > What? no, close means ummap because you need a file* attached to your vma And you miss-understood me, the vm_opts->close is the *unmap* operation not the file::close() operation. I meant memory-cl_flush on unmap before the vma goes away. > This guy definitely needs an msync/fsync at the end to make sure that the > m-write becomes durable. > Exactly done at unmap time. > 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. > So above is not relevant, and we are doing that. taking care of cpu-cache flushing. This is not disk-flushing, on a long memcpy from usermode most of the data is already durable, is only the leftover margins. Like the dax_io in the kernel dax implies direct_io always, all we are trying is to have the least performance hit in memory-cache-flushing. IS nothing to do with the text above. >> The first 3 are supported with above, because what happens is that at [3] >> the fsync actually happens on unmap and fsync is redundant in that case. >> >> The only broken scenario is [3]. We do not have a list of "dax-dirty" inodes >> per sb to iterate on and call inode-sync on. This cause problems mostly in >> freeze because with actual [3] scenario the file will be eventually closed >> and persistent, but after the call to sync returns. >> >> Its on my TODO to fix [3] based on instructions from Dave. >> The mmap call will put the inode on the list and the dax_vm_close will >> remove it. One of the regular dirty list should be used as suggested by >> Dave. > > I believe in the above two paragraphs you meant [4], so the > > 4. open mmap m-write sync ... > > case needs to be fixed so that we can detect DAX-dirty inodes? > Yes I'll be working on sync (DAX-dirty-i_list) soon but it needs a working fsync to be in place (eg: dax_fsync(inode)) Thanks Boaz -- 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
