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From:   Olga Kornievskaia <olga.kornievskaia@gmail.com>
Date:   Mon, 23 Nov 2020 12:59:43 -0500
Message-ID: <CAN-5tyEd8iDfEW0WsXyPsoM73tUSAXQgyhAfRbRbRZCem_cwPw@mail.gmail.com>
Subject: Re: [PATCH 1/1] NFSv4.2: fix LISTXATTR buffer receive size
To:     Chuck Lever <chuck.lever@oracle.com>
Cc:     Frank van der Linden <fllinden@amazon.com>,
        Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
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On Mon, Nov 23, 2020 at 12:37 PM Chuck Lever <chuck.lever@oracle.com> wrote:
>
>
>
> > On Nov 23, 2020, at 11:42 AM, Olga Kornievskaia <olga.kornievskaia@gmail.com> wrote:
> >
> > Hi Frank, Chuck,
> >
> > I would like your option on how LISTXATTR is supposed to work over
> > RDMA. Here's my current understanding of why the listxattr is not
> > working over the RDMA.
> >
> > This happens when the listxattr is called with a very small buffer
> > size which RDMA wants to send an inline request. I really dont
> > understand why, Chuck, you are not seeing any problems with hardware
> > as far as I can tell it would have the same problem because the inline
> > threshold size would still make this size inline.
> > rcprdma_inline_fixup() is trying to write to pages that don't exist.
> >
> > When LISTXATTR sets this flag XDRBUF_SPARSE_PAGES there is code that
> > will allocate pages in xs_alloc_sparse_pages() but this is ONLY for
> > TCP. RDMA doesn't have anything like that.
> >
> > Question: Should there be code added to RDMA that will do something
> > similar when it sees that flag set?
>
> Isn't the logic in rpcrdma_convert_iovs() allocating those pages?

No, rpcrdm_convert_iovs is only called for when you have reply chunks,
lists etc but not for the inline messages. What am I missing?


> > Or, should LISTXATTR be re-written
> > to be like READDIR which allocates pages before calling the code.
>
> AIUI READDIR reads into the directory inode's page cache. I recall
> that Frank couldn't do that for LISTXATTR because there's no
> similar page cache associated with the xattr listing.
>
> That said, I would prefer that the *XATTR procedures directly
> allocate pages instead of relying on SPARSE_PAGES, which is a hack
> IMO. I think it would have to use alloc_page() for that, and then
> ensure those pages are released when the call has completed.
>
> I'm not convinced this is the cause of the problem you're seeing,
> though.
>
> --
> Chuck Lever
>
>
>