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
