On Thu, 1 Dec 2016 09:37:48 -0700 Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> wrote: > Tracepoints are the standard way to capture debugging and tracing > information in many parts of the kernel, including the XFS and ext4 > filesystems. Create a tracepoint header for FS DAX and add the first DAX > tracepoints to the PMD fault handler. This allows the tracing for DAX to > be done in the same way as the filesystem tracing so that developers can > look at them together and get a coherent idea of what the system is doing. > > I added both an entry and exit tracepoint because future patches will add > tracepoints to child functions of dax_iomap_pmd_fault() like > dax_pmd_load_hole() and dax_pmd_insert_mapping(). We want those messages to > be wrapped by the parent function tracepoints so the code flow is more > easily understood. Having entry and exit tracepoints for faults also > allows us to easily see what filesystems functions were called during the > fault. These filesystem functions get executed via iomap_begin() and > iomap_end() calls, for example, and will have their own tracepoints. > > For PMD faults we primarily want to understand the type of mapping, the > fault flags, the faulting address and whether it fell back to 4k faults. > If it fell back to 4k faults the tracepoints should let us understand why. > > I named the new tracepoint header file "fs_dax.h" to allow for device DAX > to have its own separate tracing header in the same directory at some > point. > > Here is an example output for these events from a successful PMD fault: > > big-1441 [005] .... 32.582758: xfs_filemap_pmd_fault: dev 259:0 ino > 0x1003 > > big-1441 [005] .... 32.582776: dax_pmd_fault: dev 259:0 ino 0x1003 > shared WRITE|ALLOW_RETRY|KILLABLE|USER address 0x10505000 vm_start > 0x10200000 vm_end 0x10700000 pgoff 0x200 max_pgoff 0x1400 > > big-1441 [005] .... 32.583292: dax_pmd_fault_done: dev 259:0 ino 0x1003 > shared WRITE|ALLOW_RETRY|KILLABLE|USER address 0x10505000 vm_start > 0x10200000 vm_end 0x10700000 pgoff 0x200 max_pgoff 0x1400 NOPAGE > > Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> > Suggested-by: Dave Chinner <david@xxxxxxxxxxxxx> > Reviewed-by: Jan Kara <jack@xxxxxxx> Acked-by: Steven Rostedt <rostedt@xxxxxxxxxxx> -- Steve -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>