Updates:
Summary: A benchmark that only compiles code runs out of memory.
Status: WorkingAsIntended
Cc: -erik.corry
Labels: -HW-x64 HW-All
Comment #1 on issue 458 by [email protected]: A benchmark that only
compiles code runs out of memory.
http://code.google.com/p/v8/issues/detail?id=458
The compilation cache saves scripts, and links them to their compiled
versions, for
five generations, where each mark-sweep or mark-compact garbage collection
is a
generation. If all a program does is compile scripts, this can allocate
enough
memory, and keep it alive for five generations, so that the total memory
keeps on
growing, even though each compiled script is eventually discarded.
We investigated various ways to count how much memory is being kept alive
by the
compilation cache, and to put a limit on it, but they either gave useless
numbers, or
were too invasive. Even with a good number for this, it is not clear how
we would
want to limit it.
Reducing the number of generations in the compilation cache does mitigate
the
problem, but not much. Reducing from 5 to 4 has no real effect, due to a
strange
pattern in cache sizes. Reducing from 5 to 3 has a big effect - memory
keeps
growing, but much more slowly. But the number of generations was tuned by
measuring
histograms of user browser use, and the 4th and 5th generations hit about
5%-10% of
the time, making them worthwhile.
Unless we see any case where this arises in actual browser use, I think
this is a
problem with the benchmark, not with V8. We should keep this issue in mind
for
memory-constrained platforms, though, and consider one option - pre-aging
scripts
when they first enter the cache, placing them in generation 2, and only
bumping them
to generation 0 when they are hit.
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