On Mon, 2018-12-03 at 11:47 -0800, Dan Williams wrote: > On Mon, Dec 3, 2018 at 11:25 AM Alexander Duyck > <alexander.h.duyck@xxxxxxxxxxxxxxx> wrote: > > > > Add a means of exposing if a pagemap supports refcount pinning. I am doing > > this to expose if a given pagemap has backing struct pages that will allow > > for the reference count of the page to be incremented to lock the page > > into place. > > > > The KVM code already has several spots where it was trying to use a > > pfn_valid check combined with a PageReserved check to determien if it could > > take a reference on the page. I am adding this check so in the case of the > > page having the reserved flag checked we can check the pagemap for the page > > to determine if we might fall into the special DAX case. > > > > Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx> > > --- > > drivers/nvdimm/pfn_devs.c | 2 ++ > > include/linux/memremap.h | 5 ++++- > > include/linux/mm.h | 11 +++++++++++ > > 3 files changed, 17 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/nvdimm/pfn_devs.c b/drivers/nvdimm/pfn_devs.c > > index 6f22272e8d80..7a4a85bcf7f4 100644 > > --- a/drivers/nvdimm/pfn_devs.c > > +++ b/drivers/nvdimm/pfn_devs.c > > @@ -640,6 +640,8 @@ static int __nvdimm_setup_pfn(struct nd_pfn *nd_pfn, struct dev_pagemap *pgmap) > > } else > > return -ENXIO; > > > > + pgmap->support_refcount_pinning = true; > > + > > There should be no dev_pagemap instance instance where this isn't > true, so I'm missing why this is needed? I thought in the case of HMM there were instances where you couldn't pin the page, isn't there? Specifically I am thinking of the definition of MEMORY_DEVICE_PUBLIC: Device memory that is cache coherent from device and CPU point of view. This is use on platform that have an advance system bus (like CAPI or CCIX). A driver can hotplug the device memory using ZONE_DEVICE and with that memory type. Any page of a process can be migrated to such memory. However no one should be allow to pin such memory so that it can always be evicted. It sounds like MEMORY_DEVICE_PUBLIC and MMIO would want to fall into the same category here in order to allow a hot-plug event to remove the device and take the memory with it, or is my understanding on this not correct? Thanks. - Alex
