On Mon, Jun 29, 2015 at 04:02:30PM -0400, Matthew Wilcox wrote: > From: Matthew Wilcox <willy@xxxxxxxxxxxxxxx> > > Without this patch, accesses to a file on a filesystem on a block device > could be done without the page cache, but accessing the block device > itself would always go through the page cache. > > Now reads and writes to a block device that is capable of DAX will always > bypass the page cache. Loads and stores to an mmapped block device will > bypass the page cache if the user specified O_DIRECT. This opt-in from > the user is necessary because DAX mappings are currently incompatible > with RDMA and O_DIRECT I/Os with non-DAX files. Using O_DIRECT for this seems like a pretty horrible hack, so I'd like to see a really good justification of using this over other interfaces. Also it needs a Cc to linux-api and an entry in the open man page, and and even better explanation of why we only support this interface on block devices but not file systems. Last but least I supect we'll need a runtime option for direct_access support in the brd devices, as we're now going to use the regular block device path less and less. -- 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
