On 07/03/2015 10:07 PM, Theodore Ts'o wrote: > On Fri, Jul 03, 2015 at 02:48:24PM -0400, Matthew Wilcox wrote: >> >> At boot, I "modprobe pmem". > > Is there a reason why it's important to build and load pmem as a > module? If I use CONFIG_BLK_DEV_PMEM=y (which is more convenient > given how I launch my KVM test appliance), should I expect any > problems? > This (=y) should work fine. We use it a lot. (with KVM even boot an image with -dax, with a trick) Note that DAX need not be tested with pmem only, you can always use brd at any given point without any reboot. One more trick for xfstest I use: memmap=2G!4G,2G!6G And have two pmem0/1 and don't need to bother with any fdisk. Do need to mkfs every boot though. BTW: with kvm a reboot with above memmap will give you back the exact same memory. halt and "virsh start" is a different story. > I assume that this won't detect any bugs caused by missing CLFLUSH > instructions, but I assume that when using NVM as a block device, this > isn't much of an issue, as long as we don't care about torn writes? > (How using NVM with metdata checksums, or any checksums for that > matter, seems to be an interesting question --- how do we recover from > a checksum failure after a power failure?) > Currently pmem maps a very-(very) slow ioremap_nocache. So any Kernel memory access should be pmem persistent. For a real world faster ioremap, there are few major pieces still missing in the stack to make it persistent. Note the even today with ioremap_nocache, any application mmap (like git) is not persistent. > - Ted Cheers Boaz -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
