linux-kernel - Re: [RFC PATCH rdma-next 01/10] RDMA: mr: Introduce is

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Date:   Tue, 18 Jan 2022 08:55:20 +0000
From:   "lizhijian@...itsu.com" <lizhijian@...itsu.com>
To:     Dan Williams <dan.j.williams@...el.com>
CC:     Jason Gunthorpe <jgg@...pe.ca>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "zyjzyj2000@...il.com" <zyjzyj2000@...il.com>,
        "aharonl@...dia.com" <aharonl@...dia.com>,
        "leon@...nel.org" <leon@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mbloch@...dia.com" <mbloch@...dia.com>,
        "liangwenpeng@...wei.com" <liangwenpeng@...wei.com>,
        "yangx.jy@...itsu.com" <yangx.jy@...itsu.com>,
        "rpearsonhpe@...il.com" <rpearsonhpe@...il.com>,
        "y-goto@...itsu.com" <y-goto@...itsu.com>
Subject: Re: [RFC PATCH rdma-next 01/10] RDMA: mr: Introduce is_pmem



On 17/01/2022 02:11, Dan Williams wrote:
> On Wed, Jan 5, 2022 at 10:13 PM lizhijian@...itsu.com
> <lizhijian@...itsu.com> wrote:
>>
>> 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@...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.
> Apologies for the delay in responding.
>
> The Subject line of this patch is confusing, if you want to know if a
> pfn is in persistent memory the only mechanism for that is:
>
> region_intersects(addr, length, IORESOURCE_MEM, IORES_DESC_PERSISTENT_MEMORY)
>
> ...there is otherwise nothing pmem specific about the dev_pagemap
> infrastructure. Yes, pmem is the primary user, but it is also used for
> mapping "soft-reserved" memory (See: the EFI_MEMORY_SP) attribute, and
> other users.
>
> Can you clarify the intent? I am missing some context.

thanks for your help @Dan

I'm going to implement a new ibvers called RDMA FLUSH, it will support global visibility
and persistence placement type.

In my first design, only pmem can support persistence placement type, so i need to introduce
new attribute is_pmem to RDMA memory region where it associates to a user space address iova
so that i can reject a persistence placement type to DRAM(non-pmem).

Thanks
Zhijian