Re: [gofrontend-dev] libgo patch committed: Fix madvise on systems with page size != 4096

[Michael Hudson-Doyle <michael dot hudson at linaro dot org>]

"'Ian Lance Taylor <iant@google.com>' via gofrontend-dev"
<gofrontend-dev@googlegroups.com> writes:

> This patch from Anton Blanchard fixes libgo to adjust to the system page
> size when calling madvise.  Bootstrapped and ran Go testsuite on
> x86_64-unknown-linux-gnu.  Committed to mainline and 4.9 branch.

Hi, I think this patch will make my Canonical colleagues very happy (and
me when I get around to building a 64k page arm64 kernel...).  It looks
to me like this is also a problem in the gc runtime library though --
should the patch be sent there too?  (Apologies if it already has and I
missed it, I did look though).

Cheers,
mwh

> Ian
>
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> diff -r 3a53301d24d7 libgo/runtime/mheap.c
> --- a/libgo/runtime/mheap.c	Tue Apr 22 16:43:35 2014 -0700
> +++ b/libgo/runtime/mheap.c	Thu Apr 24 21:18:35 2014 -0700
> @@ -387,7 +387,7 @@
>  static uintptr
>  scavengelist(MSpan *list, uint64 now, uint64 limit)
>  {
> -	uintptr released, sumreleased;
> +	uintptr released, sumreleased, start, end, pagesize;
>  	MSpan *s;
>  
>  	if(runtime_MSpanList_IsEmpty(list))
> @@ -400,7 +400,17 @@
>  			mstats.heap_released += released;
>  			sumreleased += released;
>  			s->npreleased = s->npages;
> -			runtime_SysUnused((void*)(s->start << PageShift), s->npages << PageShift);
> +
> +			start = s->start << PageShift;
> +			end = start + (s->npages << PageShift);
> +
> +			// Round start up and end down to ensure we
> +			// are acting on entire pages.
> +			pagesize = getpagesize();
> +			start = ROUND(start, pagesize);
> +			end &= ~(pagesize - 1);
> +			if(end > start)
> +				runtime_SysUnused((void*)start, end - start);
>  		}
>  	}
>  	return sumreleased;