lkml.org 
[lkml]   [2017]   [Jun]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    SubjectRe: [PATCH V2 1/1] net: cdc_ncm: Reduce memory use when kernel memory low
    From
    From: Jim Baxter <jim_baxter@mentor.com>
    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@mentor.com>

    If someone could review this patch, I remember this issue being discussed
    a while ago, I would really appreciate it.

    \
     
     \ /
      Last update: 2017-06-30 23:15    [W:4.338 / U:0.120 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site