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.christian@oracle.com> À: "core-libs-dev" <core-libs-dev@openjdk.java.net>, "hotspot-dev" <hotspot-dev@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....