Re: [PATCH] NFSv4.2: improve page handling for GETXATTR

From: Frank van der Linden <fllinden@amazon.com>
To: Olga Kornievskaia <aglo@umich.edu>
Cc: Trond Myklebust <trondmy@hammerspace.com>,
	"linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
	"anna.schumaker@netapp.com" <anna.schumaker@netapp.com>,
	"chuck.lever@oracle.com" <chuck.lever@oracle.com>
Subject: Re: [PATCH] NFSv4.2: improve page handling for GETXATTR
Date: Wed, 2 Dec 2020 00:36:43 +0000	[thread overview]
Message-ID: <20201202003643.GB720@dev-dsk-fllinden-2c-c1893d73.us-west-2.amazon.com> (raw)
In-Reply-To: <CAN-5tyGxTi0uLMWmMwZdfFMvobBb_aw9Pa4J7sYJW__jaOvv_g@mail.gmail.com>

On Tue, Dec 01, 2020 at 06:03:31PM -0500, Olga Kornievskaia wrote:
> On Tue, Dec 1, 2020 at 5:15 PM Trond Myklebust <trondmy@hammerspace.com> wrote:
> >
> > On Tue, 2020-12-01 at 21:31 +0000, Frank van der Linden wrote:
> > > XDRBUF_SPARSE_PAGES can cause problems for the RDMA transport,
> > > and it's easy enough to allocate enough pages for the request
> > > up front, so do that.
> > >
> > > Also, since we've allocated the pages anyway, use the full
> > > page aligned length for the receive buffer. This will allow
> > > caching of valid replies that are too large for the caller,
> > > but that still fit in the allocated pages.
> > >
> > > Signed-off-by: Frank van der Linden <fllinden@amazon.com>
> > > ---
> > >  fs/nfs/nfs42proc.c | 39 ++++++++++++++++++++++++++++++---------
> > >  fs/nfs/nfs42xdr.c  | 22 +++++++++++++++++-----
> > >  2 files changed, 47 insertions(+), 14 deletions(-)
> > >
> > > diff --git a/fs/nfs/nfs42proc.c b/fs/nfs/nfs42proc.c
> > > index 2b2211d1234e..bfe15ac77bd9 100644
> > > --- a/fs/nfs/nfs42proc.c
> > > +++ b/fs/nfs/nfs42proc.c
> > > @@ -1176,11 +1176,9 @@ static ssize_t _nfs42_proc_getxattr(struct
> > > inode *inode, const char *name,
> > >                                 void *buf, size_t buflen)
> > >  {
> > >         struct nfs_server *server = NFS_SERVER(inode);
> > > -       struct page *pages[NFS4XATTR_MAXPAGES] = {};
> > > +       struct page **pages;
> > >         struct nfs42_getxattrargs arg = {
> > >                 .fh             = NFS_FH(inode),
> > > -               .xattr_pages    = pages,
> > > -               .xattr_len      = buflen,
> > >                 .xattr_name     = name,
> > >         };
> > >         struct nfs42_getxattrres res;
> > > @@ -1189,12 +1187,31 @@ static ssize_t _nfs42_proc_getxattr(struct
> >
> > Why can't we set up the page array in nfs42_proc_getxattr()? This means
> > that if we get a retryable error from the server, then we perform
> > multiple allocations of the same buffer.
> 
> I wonder if the same then is needed for the LISTXATTR as we allocated
> pages in _nfs42_proc_listxattr() and instead should do it in
> nfs42_proc_listxattr()....

There are a few more places of which this is true, yep. getactl is the
other one.

In any case, fixed for the getxattr case in v2.

- Frank