8242480: Negative value may be returned by getFreeSwapSpaceSize() in the docker(Internet mail)

[David Holmes]

Hi Jie,

On 16/04/2020 11:23 pm, jiefu(傅杰) wrote:
> Hi Severin,
> 
> Thanks for your review and very nice suggestions.
> 
> Updated: http://cr.openjdk.java.net/~jiefu/8242480/webrev.01/
> 
> test/hotspot/jtreg/containers/docker/TestGetFreeSwapSpaceSize.java is added to reproduce the bug.


Can you please use the standard OpenJDK file header after your Tencent 
copyright line:

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.
  *
  * This code is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  * version 2 for more details (a copy is included in the LICENSE file that
  * accompanied this code).
  *
  * You should have received a copy of the GNU General Public License 
version
  * 2 along with this work; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  */

I don't think the "classpath exception" is relevant to tests - certainly 
other tests I checked do not have it.

Thanks,
David
-----

> Thanks a lot.
> Best regards,
> Jie
> 
> 
> On 2020/4/16, 4:40 PM, "Severin Gehwolf" <sgehwolf at redhat.com> wrote:
> 
>      Hi Jie,
>      
>      On Fri, 2020-04-10 at 01:49 +0000, jiefu(傅杰) wrote:
>      > Hi all,
>      >
>      > JBS:    https://bugs.openjdk.java.net/browse/JDK-8242480
>      > Webrev: http://cr.openjdk.java.net/~jiefu/8242480/webrev.00/
>      >
>      > Negative values were returned by getFreeSwapSpaceSize() in our docker testing.
>      > The reason is that current implementation doesn't consider the situation when memory.limit_in_bytes == memory.memsw.limit_in_bytes, which means do not use the swap space at all.
>      >
>      > In src/jdk.management/unix/classes/com/sun/management/internal/OperatingSystemImpl.java, let's see
>      > ------------------------------------------------
>      >  71     public long getFreeSwapSpaceSize() {
>      >  72         if (containerMetrics != null) {
>      >  73             long memSwapLimit = containerMetrics.getMemoryAndSwapLimit();
>      >  74             long memLimit = containerMetrics.getMemoryLimit();
>      >  75             if (memSwapLimit >= 0 && memLimit >= 0) {
>      >  76                 for (int attempt = 0; attempt < MAX_ATTEMPTS_NUMBER; attempt++) {
>      >  77                     long memSwapUsage = containerMetrics.getMemoryAndSwapUsage();
>      >  78                     long memUsage = containerMetrics.getMemoryUsage();
>      >  79                     if (memSwapUsage > 0 && memUsage > 0) {
>      >  80                         // We read "memory usage" and "memory and swap usage" not atomically,
>      >  81                         // and it's possible to get the negative value when subtracting these two.
>      >  82                         // If this happens just retry the loop for a few iterations.
>      >  83                         if ((memSwapUsage - memUsage) >= 0) {
>      >  84                             return memSwapLimit - memLimit - (memSwapUsage - memUsage);
>      >  85                         }
>      >  86                     }
>      >  87                 }
>      >  88             }
>      >  89         }
>      >  90         return getFreeSwapSpaceSize0();
>      >  91     }
>      > ------------------------------------------------
>      > If memSwapLimit (@line 73) equals memLimit (@line 74), then getFreeSwapSpaceSize() may return a negative value @line 84.
>      >
>      > It would be better to fix it.
>      > Could you please review it and give me some advice?
>      
>      Would this be reproducible via a test? There is
>      test/hotspot/jtreg/containers/docker/TestMemoryAwareness.java which
>      contains testOperatingSystemMXBeanAwareness() tests.
>      
>      It would be good to capture this in a test somehow.
>      
>      Thanks,
>      Severin
>      
>      
>      
>