Return-Path: linux-nfs-owner@vger.kernel.org Received: from mail-wg0-f44.google.com ([74.125.82.44]:59485 "EHLO mail-wg0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751688AbaIXL4D (ORCPT ); Wed, 24 Sep 2014 07:56:03 -0400 Received: by mail-wg0-f44.google.com with SMTP id z12so2229127wgg.15 for ; Wed, 24 Sep 2014 04:56:01 -0700 (PDT) Message-ID: <5422B14C.3040502@dev.mellanox.co.il> Date: Wed, 24 Sep 2014 14:55:56 +0300 From: Sagi Grimberg MIME-Version: 1.0 To: Steve Wise , fields@fieldses.org CC: linux-rdma@vger.kernel.org, linux-nfs@vger.kernel.org Subject: Re: [PATCH V3] svcrdma: advertise the correct max payload References: <20140923221122.24227.91718.stgit@build.ogc.int> In-Reply-To: <20140923221122.24227.91718.stgit@build.ogc.int> Content-Type: text/plain; charset=UTF-8; format=flowed Sender: linux-nfs-owner@vger.kernel.org List-ID: On 9/24/2014 1:11 AM, Steve Wise wrote: > Svcrdma currently advertises 1MB, which is too large. The correct value > is the minimum of RPCSVC_MAXPAYLOAD and 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. > Maybe I'm a bit late with this, but can you explain why SG table is limited to 64 (fastreg MR and page_list probably bound it). Where is it coming from? Naturally it needs to be bound by some figure, but why 64? Sorry if I'm nit-picking on this pretty straight-forward bug fix... Sagi.