Return-Path: linux-nfs-owner@vger.kernel.org Received: from userp1040.oracle.com ([156.151.31.81]:38658 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751730AbaIVTQY convert rfc822-to-8bit (ORCPT ); Mon, 22 Sep 2014 15:16:24 -0400 Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) Subject: Re: [PATCH] svcrdma: Advertise the correct max payload From: Chuck Lever In-Reply-To: <20140922185550.GC26763@fieldses.org> Date: Mon, 22 Sep 2014 12:16:12 -0700 Cc: Steve Wise , Linux NFS Mailing List , linux-rdma@vger.kernel.org Message-Id: <0E95FC1E-753A-484C-B961-329720A657D8@oracle.com> References: <20140922183653.19376.14276.stgit@build.ogc.int> <20140922183922.GB26763@fieldses.org> <54206D7F.6070603@opengridcomputing.com> <20140922185550.GC26763@fieldses.org> To: "J. Bruce Fields" Sender: linux-nfs-owner@vger.kernel.org List-ID: On Sep 22, 2014, at 11:55 AM, J. Bruce Fields wrote: > On Mon, Sep 22, 2014 at 01:42:07PM -0500, Steve Wise wrote: >> On 9/22/2014 1:39 PM, J. Bruce Fields wrote: >>> On Mon, Sep 22, 2014 at 01:36:53PM -0500, Steve Wise wrote: >>>> Svcrdma currently advertises 1MB, which is too large. The correct value >>>> is the max scatter-gather allowed in an NFSRDMA IO chunk * the host page >>>> size. This bug is usually benign because the Linux X64 NFSRDMA client >>>> correctly limits the payload size to the correct value (64*4096 = 256KB). >>>> But if the Linux client is PPC64 with a 64KB page size, then the client >>>> will indeed use a payload size that will overflow the server. >>>> >>>> Signed-off-by: Steve Wise >>>> --- >>>> >>>> net/sunrpc/xprtrdma/svc_rdma_transport.c | 2 +- >>>> net/sunrpc/xprtrdma/xprt_rdma.h | 2 ++ >>>> 2 files changed, 3 insertions(+), 1 deletions(-) >>>> >>>> diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c >>>> index 374feb4..4e61880 100644 >>>> --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c >>>> +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c >>>> @@ -91,7 +91,7 @@ struct svc_xprt_class svc_rdma_class = { >>>> .xcl_name = "rdma", >>>> .xcl_owner = THIS_MODULE, >>>> .xcl_ops = &svc_rdma_ops, >>>> - .xcl_max_payload = RPCSVC_MAXPAYLOAD_TCP, >>>> + .xcl_max_payload = RPCSVC_MAXPAYLOAD_RDMA, >>>> .xcl_ident = XPRT_TRANSPORT_RDMA, >>>> }; >>>> diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h >>>> index c419498..467a77c 100644 >>>> --- a/net/sunrpc/xprtrdma/xprt_rdma.h >>>> +++ b/net/sunrpc/xprtrdma/xprt_rdma.h >>>> @@ -392,4 +392,6 @@ extern struct kmem_cache *svc_rdma_ctxt_cachep; >>>> /* Workqueue created in svc_rdma.c */ >>>> extern struct workqueue_struct *svc_rdma_wq; >>>> +#define RPCSVC_MAXPAYLOAD_RDMA (RPCRDMA_MAX_DATA_SEGS << PAGE_SHIFT) >>> Do you want to define this as the minimum of this and >>> RPCSVC_MAXPAYLOAD_TCP, in case RPCRDMA_MAX_DATA_SEGS gets increased some >>> day? >> >> Why would it need to be limited by MAXPAYLOAD_TCP? > > Because you're also limited by the size of the rq_pages array, which is > determined by RPCSVC_MAXPAGES, calculated from RPCSVC_MAXPAYLOAD. > > (Actually you probably want RPCSVC_MAXPAYLOAD, not MAXPAYLOAD_TCP.) Agree with this last bit. -- Chuck Lever chuck[dot]lever[at]oracle[dot]com