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List:       openjdk-hotspot-runtime-dev
Subject:    UseLargePages and 1g page size?
From:       linuxhippy () gmail ! com (Clemens Eisserer)
Date:       2008-04-10 21:34:23
Message-ID: 194f62550804101434l40cbdd9bg5ad35d3ce0e08247 () mail ! gmail ! com
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Hi John,

Thanks a lot for the detailed explanation :)
Wow, I am every time again amazed about the cleverness of hotspot's
implementation - its really cool!

Thanks, lg Clemens

> HotSpot uses the mmap APIs to get large pages only for selected
>  regions--the java heap, code cache, card table, parallel old bit map
>  and parallel old region table.  Whether to use large pages is decided
>  independently for each region, depending on how big it is and what
>  page sizes are available.  So it doesn't waste large pages for small
>  regions.
>
>  However, if on solaris you used
>
>         ppgsz -o anon=1g java ...
>
>  to set the default page size for anonymous regions to 1G, then HotSpot
>  would waste 1G for the safepoint polling page.  But that would
>  probably be the least of your problems :-).
>
>
>  -John
>
>
>  > 2008/4/8, John Coomes <John.Coomes at sun.com>:
>  > > Jon Masamitsu (Jon.Masamitsu at Sun.COM) wrote:
>  > >  > Does UseLargePages currently work with 1g large
>  > >  > page size?
>  > >  >
>  > >  > -XX:LargePageSizeInBytes=1073741824
>  > >  >
>  > >  > This is on solaris amd64
>  > >
>  > >
>  > > It should work, but AFAIK has not been tested.
>  > >
>  > >  BTW, does solaris have support for 1G pages now?  I wasn't sure it was
>  > >  available.  If you have a box, pagesize -a will tell you.
>  > >
>  > >
>  > >  -John
>  > >
>  > >
>
>


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