On Sat, 2015-08-15 at 08:44 -0700, Dan Williams wrote: > On Sat, Aug 15, 2015 at 2:19 AM, Christoph Hellwig <hch@xxxxxx> wrote: > > On Thu, Aug 13, 2015 at 10:51:11AM -0600, Ross Zwisler wrote: > >> Update the annotation for the kaddr pointer returned by direct_access() > >> so that it is a __pmem pointer. This is consistent with the PMEM driver > >> and with how this direct_access() pointer is used in the DAX code. > > > > IFF we stick to the __pmem annotations this looks good. > > > > That beeing said I start to really dislike them. We don't special > > accesors to read/write from pmem, we just need to explicitly commit > > it if we want to make it persistent. So I really don't see the need > > to treat it special and require all the force casts to and from the > > attribute. > > I'm not going to put up much of a fight if it's really getting in the way.... > > That said, while we don't need special accessors we do need guarantees > that anything that has written to a persistent memory address has done > so in a way that wmb_pmem() is able to flush it. It's more of a "I've > audited this code path for wmb_pmem() compatibility so use this api to > write to pmem." > > Perhaps a better way to statically check for missed flushes might be > to have acquire_pmem_for_write() + release() annotations and the final > release does a wmb_pmem(), but as far as I can tell the sparse > acquire/release annotations don't stack. FWIW I've been on the fence about the __pmem annotations, but my current thought is that we really do need a way of saying that stores to these pointers need special care for wmb_pmem() to do its thing and that __pmem does a reasonably good job of that. If we can figure out a cooler way, such as the write() + release() flow Dan is talking about, great. But I think we need something to keep us from making errors by storing to PMEM pointers and leaving data in the processor cache. -- 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
