[m-rev.] for review: Enable munmap support in Boehm GC by default.
jfischer at opturion.com
Wed Jul 22 21:54:49 AEST 2020
On Wed, 22 Jul 2020, Peter Wang wrote:
> Memory unmapping support is useful for long running programs to return
> unused memory pages back to the OS, e.g. a server process can reduce the
> amount of physical memory it occupies during idle periods.
> Previously the user building the Mercury system needed to enable munmap
> support at configure time. In 2008 I wrote:
> Allow the use of munmap() in Boehm GC, in order to return unused
> memory pages back to the OS. This has an adverse effect on run times
> so we want to be able to enable it on a per-application basis.
> Bdwgc upstream has more recently enabled munmap support by default on
> the master branch (albeit, not the v7.6.x branch we currently use).
> Some testing on my machine suggests that we can try enabling munmap
> support by default:
> - in asm_fast.gc grade, there was no discernable difference to the
> compiler's performance, with or without munmap support
> - in the hlc.gc grade, the compiler ran 1-2% faster
> WITH munmap support enabled
> Tested on Linux/x86-64, time to compile the 10 largest modules in the
> arena directory.
Have you tested this on platforms other than Linux/x86_64?
> Change default value of enable_gc_mmap and enable_gc_munmap to yes.
> Invert sense of --enable-gc-mmap and --enable-gc-munmap options in
> the help text.
> Announce change.
That's fine. (If further testing reveals that it's not working on some
of the other platforms then we can disable it on those by default.)
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