On Tue, Nov 7, 2017 at 1:25 PM Remi Forax <fo...@univ-mlv.fr> wrote: > 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 ?
It’s 12 bytes (on x64) with compressed klass ptr; 8 bytes for the mark word and a 4 byte compressed klass ptr. It’s 16 bytes without compressed klass ptr. Or are you asking something else Remi? I think many folks would be upset if a boolean wasn’t stored as a byte :). > > > 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. > -- Sent from my phone
