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SubjectRe: [RFC PATCH rdma-next 01/10] RDMA: mr: Introduce is_pmem
Date

Add Dan to the party :)

May i know whether there is any existing APIs to check whether
a va/page backs to a nvdimm/pmem ?



On 06/01/2022 08:21, Jason Gunthorpe wrote:
> On Tue, Dec 28, 2021 at 04:07:08PM +0800, Li Zhijian wrote:
>> We can use it to indicate whether the registering mr is associated with
>> a pmem/nvdimm or not.
>>
>> Currently, we only assign it in rxe driver, for other device/drivers,
>> they should implement it if needed.
>>
>> RDMA FLUSH will support the persistence feature for a pmem/nvdimm.
>>
>> Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
>> drivers/infiniband/sw/rxe/rxe_mr.c | 47 ++++++++++++++++++++++++++++++
>> include/rdma/ib_verbs.h | 1 +
>> 2 files changed, 48 insertions(+)
>>
>> diff --git a/drivers/infiniband/sw/rxe/rxe_mr.c b/drivers/infiniband/sw/rxe/rxe_mr.c
>> index 7c4cd19a9db2..bcd5e7afa475 100644
>> +++ b/drivers/infiniband/sw/rxe/rxe_mr.c
>> @@ -162,6 +162,50 @@ void rxe_mr_init_dma(struct rxe_pd *pd, int access, struct rxe_mr *mr)
>> mr->type = IB_MR_TYPE_DMA;
>> }
>>
>> +// XXX: the logic is similar with mm/memory-failure.c
>> +static bool page_in_dev_pagemap(struct page *page)
>> +{
>> + unsigned long pfn;
>> + struct page *p;
>> + struct dev_pagemap *pgmap = NULL;
>> +
>> + pfn = page_to_pfn(page);
>> + if (!pfn) {
>> + pr_err("no such pfn for page %p\n", page);
>> + return false;
>> + }
>> +
>> + p = pfn_to_online_page(pfn);
>> + if (!p) {
>> + if (pfn_valid(pfn)) {
>> + pgmap = get_dev_pagemap(pfn, NULL);
>> + if (pgmap)
>> + put_dev_pagemap(pgmap);
>> + }
>> + }
>> +
>> + return !!pgmap;
> You need to get Dan to check this out, but I'm pretty sure this should
> be more like this:
>
> if (is_zone_device_page(page) && page->pgmap->type == MEMORY_DEVICE_FS_DAX)

Great, i have added him.



>
>
>> +static bool iova_in_pmem(struct rxe_mr *mr, u64 iova, int length)
>> +{
>> + struct page *page = NULL;
>> + char *vaddr = iova_to_vaddr(mr, iova, length);
>> +
>> + if (!vaddr) {
>> + pr_err("not a valid iova %llu\n", iova);
>> + return false;
>> + }
>> +
>> + page = virt_to_page(vaddr);
> And obviously this isn't uniform for the entire umem, so I don't even
> know what this is supposed to mean.

My intention is to check if a memory region belongs to a nvdimm/pmem.
The approach is like that:
iova(user space)-+ +-> page -> page_in_dev_pagemap()
| |
+-> va(kernel space) -+
Since current MR's va is associated with map_set where it record the relations
between iova and va and page. Do do you mean we should travel map_set to
get its page ? or by any other ways.







>> diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
>> index 6e9ad656ecb7..822ebb3425dc 100644
>> +++ b/include/rdma/ib_verbs.h
>> @@ -1807,6 +1807,7 @@ struct ib_mr {
>> unsigned int page_size;
>> enum ib_mr_type type;
>> bool need_inval;
>> + bool is_pmem;
> Or why it is being stored in the global struct?

Indeed, it's not strong necessary. but i think is_pmem should belongs to a ib_mr
so that it can be checked by other general code when they needed even though no
one does such checking so far.


Thanks
Zhijian



>
> Jason
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