Messages in this thread | | | Date | Mon, 22 Jun 2015 18:45:15 +0200 | From | Christoph Hellwig <> | Subject | Re: [PATCH 14/15] libnvdimm: support read-only btt backing devices |
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On Mon, Jun 22, 2015 at 09:36:50AM -0700, Dan Williams wrote: > In that case "don't stack" is too coarse of a hammer. I see this as a > request to hide the subordinate ULD which is a new capability that DM > and MD might benefit from as well. We already have the case in MD > where it internally holds a reference to bdev that has been hot > removed, it seems not much of a stretch to have stacking drivers be > able to hide device nodes for bdevs that they are holding.
I don't see why you're comparing with MD and DM here. MD and DM sit cleanly ontop of any block device. If btt was independent of libnvdimm and just used ->rw_bytes we could see it as this.
But it's all a giant entangled mess, where btt for example is probed by libnvdimm. At the same time pmem.c isn't really a true block driver, it's really just a trivial shim between the block API and pmem-style memcpy. Especially with the proper pmem API btt would become cleaner just calling that directly.
> Yes, if they want to use DAX they should do it consciously and audit > their application to be sure it is safe to abandon atomic sector > guarantees. With the current flexibility to do BTT on a partition > they can do this conversion piecemeal and, for example, keep metadata > on BTT and data on DAX.
By that logic you'd want to attach BTT by default and allow opt-out at some level. This could be a libnvmdimm-level partitioning scheme, which would also allow storing the bit if BTT is used or not persistently. Or it could be on fine grained boundaries which might be more useful. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/
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