My bad, I've calculated that the header was 8 bytes instead of 12, so I've supposed that the boolean was not stored in a byte.
For my culture, why the header is 12 bytes, the pointer to the vtable is on 64bits and can not be compressed like the other oops ? Rémi On November 7, 2017 5:42:33 PM GMT+01:00, Brent Christian <brent.christ...@oracle.com> wrote: >Hi, Remi > >Thanks for the idea. From my reading of the jol ouput: > >http://cr.openjdk.java.net/~bchristi/8185925/StackFrameInfo.jol.rmDeclClass.txt > > > >I believe retainClassRef is already being stored in a single byte (i.e. > >SIZE of 1): > > OFFSET SIZE TYPE DESCRIPTION >... > 10 1 boolean StackFrameInfo.retainClassRef > >Thanks, >-Brent > >On 11/6/17 11:45 PM, Remi Forax wrote: >> Hi Brent, >> if you declare retainClassRef as a byte, you can even compress the >data structure a little bit more, no ? >> a boolean (as a field) uses 4 bytes while a byte uses welll 1 byte. >> Given that bci is a short, the VM will put both bci and >retainClassRef on the same 32 bits slot. >> >> cheers, >> Rémi >> >> ----- Mail original ----- >>> De: "Brent Christian" <brent.christ...@oracle.com> >>> À: "core-libs-dev" <core-libs-dev@openjdk.java.net>, "hotspot-dev" ><hotspot-...@openjdk.java.net> >>> Envoyé: Mardi 7 Novembre 2017 01:23:16 >>> Objet: RFR: 8185925 & 8153682 (footprint reduction of >java.lang.StackFrameInfo) >> >>> Hi, >>> >>> There are a couple opportunities to reduce the memory footprint of >>> java.lang.StackFrameInfo (the internal implementation of >>> java.lang.StackWalker.StackFrame): >>> >>> 8153682[1] : StackFrameInfo.declaringClass could be removed >>> 8185925[2] : StackFrameInfo::walker field can be replaced with >bitmap to >>> save footprint >>> >>> I had a look using jol[3]. Removing only 'walker' helps only under >32- >>> and 64-bit, but not with compressed oops. Removing both 'walker' >and >>> 'declaringClass' brings a benefit to compressed oops as well (though >not >>> for 16-byte aligned). >>> >>> The size change, in bytes, for each execution mode is as follows: >>> >>> 32-bit: 32->24 >>> 64-bit: 56->40 >>> 64/compressed oops: 32->24 >>> 64/compressed oops, 16-byte aligned: 32->32 >>> >>> (For reference, the jol reports for the baseline and specimen are at >[4] >>> and [5], respectively.) >>> >>> Please review my code change for this. The webrev is here: >>> http://cr.openjdk.java.net/~bchristi/8185925/webrev.03/ >>> >>> An automated test run is in progress. >>> >>> Thanks! >>> -Brent >>> >>> -- >>> 1. https://bugs.openjdk.java.net/browse/JDK-8153682 >>> 2. https://bugs.openjdk.java.net/browse/JDK-8185925 >>> 3. http://openjdk.java.net/projects/code-tools/jol/ >>> 4. >>> >http://cr.openjdk.java.net/~bchristi/8185925/StackFrameInfo.jol.baseline.txt >>> 5. >>> >http://cr.openjdk.java.net/~bchristi/8185925/StackFrameInfo.jol.rmDeclClass.txt -- Sent from my Android device with K-9 Mail. Please excuse my brevity.
