On Wed 23-11-16 11:44:19, 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
>
> Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> Suggested-by: Dave Chinner <david@xxxxxxxxxxxxx>
Looks good. Just one minor comment:
> + TP_printk("%s mapping %s address %#lx vm_start %#lx vm_end %#lx "
> + "pgoff %#lx max_pgoff %#lx %s",
> + __entry->vm_flags & VM_SHARED ? "shared" : "private",
> + __entry->flags & FAULT_FLAG_WRITE ? "write" : "read",
> + __entry->address,
> + __entry->vm_start,
> + __entry->vm_end,
> + __entry->pgoff,
> + __entry->max_pgoff,
> + __print_flags(__entry->result, "|", VM_FAULT_RESULT_TRACE)
> + )
> +)
I think it may be useful to dump full 'flags', not just FAULT_FLAG_WRITE...
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
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