On Wed, Nov 23, 2016 at 11:44:19AM -0700, Ross Zwisler 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 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-2057 [000] .... 136.396855: dax_pmd_fault: shared mapping write > address 0x10505000 vm_start 0x10200000 vm_end 0x10700000 pgoff 0x200 > max_pgoff 0x1400 > > big-2057 [000] .... 136.397943: dax_pmd_fault_done: shared mapping write > address 0x10505000 vm_start 0x10200000 vm_end 0x10700000 pgoff 0x200 > max_pgoff 0x1400 NOPAGE Can we make the output use the same format as most of the filesystem code? i.e. the output starts with backing device + inode number like so: xfs_ilock: dev 8:96 ino 0x493 flags ILOCK_EXCL.... This way we can filter the output easily across both dax and filesystem tracepoints with 'grep "ino 0x493"'... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
