----- Original Message ----- > From: "Matthew Wilcox" <willy@xxxxxxxxxxxxxxx> > To: "Mathieu Desnoyers" <mathieu.desnoyers@xxxxxxxxxxxx> > Cc: "Matthew Wilcox" <willy@xxxxxxxxxxxxxxx>, "Ross Zwisler" <ross.zwisler@xxxxxxxxxxxxxxx>, "lttng-dev" > <lttng-dev@xxxxxxxxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx > Sent: Monday, October 27, 2014 2:48:09 PM > Subject: Re: Progress on system crash traces with LTTng using DAX and pmem > > 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. Hi Matthew, I've noticed that Andrew Morton picked up your DAX patchset, which is really good news! About the topic of DAX support on mtd-ram: I'm wonder if we would need the pmem patchset at all if mtd-ram gets DAX support ? How do the two approaches differ ? Has anyone tried out mtd-ram over DAX at this point ? Thanks for the great work! :) 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
