On Tue, Nov 7, 2017 at 3:45 PM Remi Forax <fo...@univ-mlv.fr> wrote: > > > On November 7, 2017 8:48:43 PM GMT+01:00, Vitaly Davidovich < > vita...@gmail.com> wrote: > >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? > > My question is more given you have compressed oops (and compressed klass) > why the header is 12 bytes and not 8 bytes (a two words header). > > so why the mark word is 8 bytes and not 4 ? At worst it's a pointer and > again you can use the compressed oops trick ?
http://hg.openjdk.java.net/jdk9/hs/hotspot/file/c68024d52834/src/share/vm/oops/markOop.hpp has a description of the layout - it’s not a pointer per se (although some states do encode one) but a bunch of metadata. > > > > > >I think many folks would be upset if a boolean wasn’t stored as a byte > >:). > > yes, right. > > Remi > > > > >> > >> > >> 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 Android device with K-9 Mail. Please excuse my brevity. > -- Sent from my phone
