Hi Matthew, Hi Ross, A quick follow up on my progress on using DAX and pmem with LTTng. I've been able to successfully gather a user-space trace into buffers mmap'd into an ext4 filesystem within a pmem block device mounted with -o dax to bypass the page cache. After a soft reboot, I'm able to mount the partition again, and gather the very last data collected in the buffers by the applications. I created a "lttng-crash" program that extracts data from those buffers and converts the content into a readable Common Trace Format trace. So I guess you have a use-case for your patchsets on commodity hardware right there. :) I've been asked by my customers if DAX would work well with mtd-ram, which they are using. To you foresee any roadblock with this approach ? FYI, the main reason why my customer wants to go with a "trace into memory that survives soft reboot" approach rather than to use things like kexec/kdump is that they care about the amount of time it takes to reboot their machines. They want a solution where they can extract the detailed crash data after reboot, after the machine is back online, rather than requiring a few minutes of offline time to extract the crash details. So I guess next year I'll probably be looking into allocating the LTTng kernel tracer buffers into an mmap'd file within a ext2/4-DAX-over-pmem/mtd-ram filesystem. It's going to be exciting! :) Please keep me in CC on your next patch versions. I'm willing to spend some more time reviewing them if needed. By the way, do you guys have a target time-frame/kernel version you aim at for getting this work upstream ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
