On Tue, Mar 08, 2016 at 02:29:58PM -0800, Dan Williams wrote: > On Tue, Mar 8, 2016 at 2:21 PM, NeilBrown <[email protected]> wrote: > > > > When alloc_disk(0) or alloc_disk-node(0, XX) is used, the ->major > > number is completely ignored: all devices are allocated with a > > major of BLOCK_EXT_MAJOR. > > > > So there is no point allocating pmem_major. > > > > Signed-off-by: NeilBrown <[email protected]> > > --- > > drivers/nvdimm/pmem.c | 19 +------------------ > > 1 file changed, 1 insertion(+), 18 deletions(-) > > > > Hi Dan et al, > > I was recently educating myself about the behavior of alloc_disk(0). > > As I understand it, the ->major is ignored and all device numbers for all > > partitions (including '0') are allocated on demand with major number of > > BLOCK_EXT_MAJOR. > > > > So I was a little surprised to find that pmem.c allocated a major > > number which is never used - historical anomaly I suspect. > > I was a bit more surprised at the comment in: > > > > Commit: 9f53f9fa4ad1 ("libnvdimm, pmem: add libnvdimm support to the pmem > > driver") > > > > "The minor numbers are also more predictable by passing 0 to alloc_disk()." > > > > How can they possibly be more predictable given that they are allocated > > on-demand? Maybe discovery order is very predictable??? > > Ross, I remember you looked into this when Boaz pointed out something similar.
I think you're probably remembering a conversation we had about BRD. https://lkml.org/lkml/2014/8/6/568 I honestly don't remember the details well enough to comment - I'd have to dig into it again and test to have an informed opinion. But, of course, if we can get rid of some useless code, we should. :) > > In any case, I propose this patch but cannot test it (beyond compiling) > > as I don't have relevant hardware. And maybe some user-space code greps > > /proc/devices for "pmem" to determine if "pmem" is compiled in (though > > I sincerely hope not). > > So I cannot be certain that this patch won't break anything, but am > > hoping that if you like it you might test it. > > Will do. > > Thanks Neil!
