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List:       openjdk-hotspot-runtime-dev
Subject:    Re: RFR: 8315923: pretouch_memory by atomic-add-0 fragments huge pages unexpectedly [v12]
From:       Thomas Stuefe <stuefe () openjdk ! org>
Date:       2023-10-30 6:49:36
Message-ID: DiMrnBC6wSPShR6V8p11k3DUEjkxHJL7sGeMibnftJw=.162d267c-5d6e-4e22-873f-d90d1567069e () github ! com
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On Mon, 30 Oct 2023 06:20:07 GMT, Liming Liu <duke@openjdk.org> wrote:

> > As described at [JDK-8315923](https://bugs.openjdk.org/browse/JDK-8315923), this \
> > patch uses madvise with MADV_POPULATE_WRITE to pretouch memory when supported \
> > (since kernel 5.14). 
> > Ran the newly added jtreg test on 64c Neoverse-N1 machines with kernel 4.18, 5.13 \
> > and 6.1, and observed that transparent huge pages formed right after pretouch on \
> > kernel 6.1. Recorded the time spent on the test in *seconds* with `VERBOSE=time` \
> > as the table below, and got that the patch takes improvements when the system \
> > call is supported, while does not hurt if not supported: 
> > <table>
> > <tr>
> > <th>Kernel</th>
> > <th colspan="2"><tt>-XX:-TransparentHugePages</tt></th>
> > <th colspan="2"><tt>-XX:+TransparentHugePages</tt></th>
> > </tr>
> > <tr><td></td><td>Unpatched</td><td>Patched</td><td>Unpatched</td><td>Patched</td></tr>
> >  <tr><td>4.18</td><td>11.30</td><td>11.30</td><td>0.25</td><td>0.25</td></tr>
> > <tr><td>5.13</td><td>0.22</td><td>0.22</td><td>3.42</td><td>3.42</td></tr>
> > <tr><td>6.1</td><td>0.27</td><td>0.33</td><td>3.54</td><td>0.33</td></tr>
> > </table>
> 
> Liming Liu has updated the pull request incrementally with one additional commit \
> since the last revision: 
> Update the name of the method

I don't have time to look at this for now and step back to wait for others. But I \
don't want to hold up this patch - if there are enough reviewers that ok it, please \
don't wait for me. 

As I wrote earlier, the patch itself is mechanically fine. The test has aspects I \
don't understand, and I am worried about concurrent usage of the \
about-to-be-pretouched area by other threads.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/15781#issuecomment-1784575980


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