Re: missing madvise functionality

[Anton Blanchard]

Hi,

> Oh.  I was assuming that we'd want to unmap these pages from pagetables and
> mark then super-easily-reclaimable.  So a later touch would incur a minor
> fault.
> 
> But you think that we should leave them mapped into pagetables so no such
> fault occurs.

That would be very nice. The issues are not limited to threaded apps,
we have seen performance problems with single threaded HPC applications
that do a lot of large malloc/frees. It turns out the continual set up
and tear down of pagetables when malloc uses mmap/free is a problem. At
the moment the workaround is:

export MALLOC_MMAP_MAX_=0 MALLOC_TRIM_THRESHOLD_=-1

which forces glibc malloc to use brk instead of mmap/free. Of course brk
is good for keeping pagetables around but bad for keeping memory usage
down.

Anton
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