-------------------------------------------------------------------------------- From: David S. Miller (davem@xxxxxxxxxxxxx) Sent: Fri, 30 Jun 2017 12:59:53 -0400 To: jim_baxter@xxxxxxxxxx Cc: linux-usb@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, oliver@xxxxxxxxxx, bjorn@xxxxxxx, David.Laight@xxxxxxxxxx Subject: Re: [PATCH V2 1/1] net: cdc_ncm: Reduce memory use when kernel memory low > From: Jim Baxter <jim_baxter@xxxxxxxxxx> > 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 <jim_baxter@xxxxxxxxxx> > > 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 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
