On Mon, Nov 28, 2016 at 03:46:51PM -0700, Ross Zwisler wrote: > On Fri, Nov 25, 2016 at 02:00:59PM +1100, Dave Chinner wrote: > > 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"'... > > I think I can include the inode number, which I have via mapping->host. Am I > correct in assuming "struct inode.i_ino" will always be the same as > "struct xfs_inode.i_ino"? Yes - just use inode.i_ino. > Unfortunately I don't have access to the major/minor (the dev_t) until I call > iomap_begin(). In general, filesystem tracing uses inode->sb->s_dev as the identifier. NFS, gfs2, XFS, ext4 and others all use this. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- 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>
