On Sat, Oct 25, 2014 at 12:51:25PM +0000, Mathieu Desnoyers wrote: > 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. :) Sweet! > 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 ? Looks like we'd need to add support to mtd-blkdevs.c for DAX. I assume they're already using one of the block-based ways to expose MTD to filesystems, rather than jffs2/logfs/ubifs? I'm thinking we might want to add a flag somewhere in the block_dev / bdi that indicates whether DAX is supported. Currently we rely on whether ->direct_access is present in the block_device_operations to indicate that, so we'd have to have two block_dev_operations in mtd-blkdevs, depending on whether direct access is supported by the underlying MTD device. Not a show-stopper. > 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 ? We're trying to get it upstream ASAP. We've been working on it publically since December last year, and it's getting frustrating that it's not upstream already. I sent a v12 a few minutes before you sent this message ... I thought git would add you to the cc's since your Reviewed-by is on some of the patches. -- 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>