On 08/08/2017 06:44 PM, Gil Tene wrote:
> On Monday, August 7, 2017 at 11:50:27 AM UTC-7, Alen Vrečko wrote:
>     Saw this a while back.
> 
>     https://shipilev.net/jvm-anatomy-park/2-transparent-huge-pages/
>     <https://shipilev.net/jvm-anatomy-park/2-transparent-huge-pages/>
> 
>     Basically using THP/defrag with madvise and using
>     -XX:+UseTransparentHugePages -XX:+AlwaysPreTouch JVM opts.
> 
>     Looks like the defrag cost should be paid in full at startup due to
>     AlwaysPreTouch. Never got around to test this in production. Just have
>     THP disabled. Thoughts?
> 
> The above flags would only cover the Java heap. In a Java application. So 
> obviously THP for non-Java
> things doesn't get helped by that.

So, this is the reason why to use THP in "madvise" mode? Then JVM madvise-s 
Java heap to THP,
upfront defrags it with AlwaysPreTouch, but native allocations stay outside of 
THP path, and thus do
not incur defrag latencies. If there is a native structure that allocates with 
madvise hint and does
heavy churn causing defrag, I'd say it should have not madvise in the first 
place.

-Aleksey

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