From: Jan Kara Subject: Re: [PATCH 3/6] dax: add tracepoint infrastructure, PMD tracing Date: Thu, 24 Nov 2016 10:16:26 +0100 Message-ID: <20161124091626.GC24138@quack2.suse.cz> References: <1479926662-21718-1-git-send-email-ross.zwisler@linux.intel.com> <1479926662-21718-4-git-send-email-ross.zwisler@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Jan Kara , Matthew Wilcox , linux-nvdimm-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org, Dave Chinner , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Steven Rostedt , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Ingo Molnar , Alexander Viro , linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Andrew Morton , linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Christoph Hellwig To: Ross Zwisler Return-path: Content-Disposition: inline In-Reply-To: <1479926662-21718-4-git-send-email-ross.zwisler-VuQAYsv1563Yd54FQh9/CA@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org Sender: "Linux-nvdimm" List-Id: linux-ext4.vger.kernel.org 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 > Suggested-by: Dave Chinner 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 SUSE Labs, CR