Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752361AbdF3RDg (ORCPT ); Fri, 30 Jun 2017 13:03:36 -0400 Received: from relay1.mentorg.com ([192.94.38.131]:32954 "EHLO relay1.mentorg.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751874AbdF3RDe (ORCPT ); Fri, 30 Jun 2017 13:03:34 -0400 Subject: Re: [PATCH V2 1/1] net: cdc_ncm: Reduce memory use when kernel memory low To: David Miller CC: , , , , , References: <1498682129-9129-1-git-send-email-jim_baxter@mentor.com> <1498682129-9129-2-git-send-email-jim_baxter@mentor.com> <20170630.125953.245673296877756318.davem@davemloft.net> From: "Baxter, Jim" Message-ID: <71a89e5d-e060-4735-32f7-d8bcc26aaeb2@mentor.com> Date: Fri, 30 Jun 2017 18:03:26 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1 MIME-Version: 1.0 In-Reply-To: <20170630.125953.245673296877756318.davem@davemloft.net> Content-Type: text/plain; charset="utf-8" Content-Language: en-GB Content-Transfer-Encoding: 7bit X-Originating-IP: [137.202.0.87] X-ClientProxiedBy: svr-ies-mbx-01.mgc.mentorg.com (139.181.222.1) To SVR-IES-MBX-04.mgc.mentorg.com (139.181.222.4) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2327 Lines: 57 -------------------------------------------------------------------------------- From: David S. Miller (davem@davemloft.net) Sent: Fri, 30 Jun 2017 12:59:53 -0400 To: jim_baxter@mentor.com Cc: linux-usb@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, oliver@neukum.org, bjorn@mork.no, David.Laight@ACULAB.COM Subject: Re: [PATCH V2 1/1] net: cdc_ncm: Reduce memory use when kernel memory low > From: Jim Baxter > Date: Wed, 28 Jun 2017 21:35:29 +0100 > >> The CDC-NCM driver can require large amounts of memory to create >> skb's and this can be a problem when the memory becomes fragmented. >> >> This especially affects embedded systems that have constrained >> resources but wish to maximise the throughput of CDC-NCM with 16KiB >> NTB's. >> >> The issue is after running for a while the kernel memory can become >> fragmented and it needs compacting. >> If the NTB allocation is needed before the memory has been compacted >> the atomic allocation can fail which can cause increased latency, >> large re-transmissions or disconnections depending upon the data >> being transmitted at the time. >> This situation occurs for less than a second until the kernel has >> compacted the memory but the failed devices can take a lot longer to >> recover from the failed TX packets. >> >> To ease this temporary situation I modified the CDC-NCM TX path to >> temporarily switch into a reduced memory mode which allocates an NTB >> that will fit into a USB_CDC_NCM_NTB_MIN_OUT_SIZE (default 2048 Bytes) >> sized memory block and only transmit NTB's with a single network frame >> until the memory situation is resolved. >> Each time this issue occurs we wait for an increasing number of >> reduced size allocations before requesting a full size one to not >> put additional pressure on a low memory system. >> >> Once the memory is compacted the CDC-NCM data can resume transmitting >> at the normal tx_max rate once again. >> >> Signed-off-by: Jim Baxter > > If someone could review this patch, I remember this issue being discussed > a while ago, I would really appreciate it. > Hello, For reference this replaces the original discussion in http://patchwork.ozlabs.org/patch/763100/ and http://patchwork.ozlabs.org/patch/766181/ Best regards, Jim