On Thu, Sep 24, 2015 at 8:15 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > On Wed, Sep 23, 2015 at 12:41:55AM -0400, Dan Williams wrote: >> Enable DAX to use a reference count for keeping the virtual address >> returned by ->direct_access() valid for the duration of its usage in >> fs/dax.c, or otherwise hold off blk_cleanup_queue() while >> pmem_make_request is active. The blk-mq code is already in a position >> to need low overhead referece counting for races against request_queue >> destruction (blk_cleanup_queue()). Given DAX-enabled block drivers do >> not enable blk-mq, share the storage in 'struct request_queue' between >> the two implementations. > > Can we just move the refcounting to common code with the same field > name, and even initialize it for non-mq, non-dax queues but just never > tage a reference there (for now)? That makes sense to me, especially because drivers/nvdimm/blk.c is broken in the same way as drivers/nvdimm/pmem.c and it would be awkward to have it use blk_dax_get() / blk_dax_put(). The percpu_refcount should be valid for all queues and it will only ever be > 1 in the blk_mq and libnvdimm cases (for now). Will fix. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>