Return-Path: linux-nfs-owner@vger.kernel.org Received: from fieldses.org ([174.143.236.118]:33159 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751563AbaIVSzu (ORCPT ); Mon, 22 Sep 2014 14:55:50 -0400 Date: Mon, 22 Sep 2014 14:55:50 -0400 From: "J. Bruce Fields" To: Steve Wise Cc: linux-nfs@vger.kernel.org, linux-rdma@vger.kernel.org Subject: Re: [PATCH] svcrdma: Advertise the correct max payload Message-ID: <20140922185550.GC26763@fieldses.org> References: <20140922183653.19376.14276.stgit@build.ogc.int> <20140922183922.GB26763@fieldses.org> <54206D7F.6070603@opengridcomputing.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <54206D7F.6070603@opengridcomputing.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: 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.) --b.