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Diffstat (limited to 'ChangeLog')
| -rw-r--r-- | ChangeLog | 50 |
1 files changed, 50 insertions, 0 deletions
@@ -1,3 +1,53 @@ +Tue Nov 5 03:31:23 2013 Koichi Sasada <ko1@atdot.net> + + * gc.c: add 3gen GC patch, but disabled as default. + + RGenGC is designed as 2 generational GC, young and old generation. + Young objects will be promoted to old objects after one GC. + Old objects are not collect until major (full) GC. + + The issue of this approach is some objects can promoted as old + objects accidentally and not freed until major GC. + Major GC is not frequently so short-lived but accidentally becoming + old objects are not freed. + + For example, the program "loop{Array.new(1_000_000)}" consumes huge + memories because short lived objects (an array which has 1M + elements) are promoted while GC and they are not freed before major + GC. + + To solve this problem, generational GC with more generations + technique is known. This patch implements three generations gen GC. + + At first, newly created objects are "Infant" objects. + After surviving one GC, "Infant" objects are promoted to "Young" + objects. + "Young" objects are promoted to "Old" objects after surviving + next GC. + "Infant" and "Young" objects are collected if it is not marked + while minor GC. So that this technique solves this problem. + + Representation of generations: + * Infant: !FL_PROMOTED and !oldgen_bitmap [00] + * Young : FL_PROMOTED and !oldgen_bitmap [10] + * Old : FL_PROMOTED and oldgen_bitmap [11] + + The macro "RGENGC_THREEGEN" enables/disables this feature, and + turned off as default because there are several problems. + (1) Failed sometimes (Heisenbugs). + (2) Performance down. + Especially on write barriers. We need to detect Young or Old + object by oldgen_bitmap. It is slower than checking flags. + + To evaluate this feature on more applications, I commit this patch. + Reports are very welcome. + + This patch includes some refactoring (renaming names, etc). + + * include/ruby/ruby.h: catch up 3gen GC. + + * .gdbinit: fix to show a prompt "[PROMOTED]" for promoted objects. + Tue Nov 5 00:05:51 2013 Koichi Sasada <ko1@atdot.net> * node.h: catch up comments for last commit. |