linux-kernel - Re: [RFC PATCH rdma-next 08/10] RDMA/rxe: Implement flush execution in responder side

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Date:   Wed, 12 Jan 2022 09:50:38 +0000
From:   "lizhijian@...itsu.com" <lizhijian@...itsu.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
CC:     "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 08/10] RDMA/rxe: Implement flush execution
 in responder side

On 12/01/2022 04:48, Jason Gunthorpe wrote:
> On Tue, Jan 11, 2022 at 05:34:36AM +0000, lizhijian@...itsu.com wrote:
>
>> Yes, that's true. that's because only pmem has ability to persist data.
>> So do you mean we don't need to prevent user to create/register a persistent
>> access flag to a non-pmem MR? it would be a bit confusing if so.
> Since these extensions seem to have a mode that is unrelated to
> persistent memory,
I can only agree with part of them, since the extensions also say that:

oA19-1: Responder shall successfully respond on FLUSH operation only
after providing the placement guarantees, as specified in the packet, of
preceding memory updates (for example: RDMA WRITE, Atomics and
ATOMIC WRITE) towards the memory region.

it mentions *shall successfully respond on FLUSH operation only
after providing the placement guarantees*. If users request a
persistent placement to a non-pmem MR without errors,  from view
of the users, they will think of their request had been *successfully responded*
that doesn't reflect the true(data was persisted).

So i think we should respond error to request side in such case.

Further more, If we have a checking during the new MR creating/registering,
user who registers this MR can know if the target MR supports persistent access flag.
Then they can tell this information to the request side so that request side can
request a valid placement type later. that is similar behavior with current librpma.

Thanks
Zhijian

>   I'm not sure it makes sense to link the two things.
>
> Jason