On Sun, Oct 16, 2011 at 8:33 PM, Andi Kleen <a...@firstfloor.org> wrote: > On Sun, Oct 16, 2011 at 12:38:16PM +0200, Richard Guenther wrote: >> On Sun, Oct 16, 2011 at 7:30 AM, Andi Kleen <a...@firstfloor.org> wrote: >> > Andi Kleen <a...@firstfloor.org> writes: >> > >> >> From: Andi Kleen <a...@linux.intel.com> >> >> >> >> Use the Linux MADV_DONTNEED call to unmap free pages in the garbage >> >> collector.Then keep the unmapped pages in the free list. This avoid >> >> excessive memory fragmentation on large LTO bulds, which can lead >> >> to gcc bumping into the Linux vm_max_map limit per process. >> > >> > Could I have a decision on this patch please? The problem in PR50636 >> > is still there and this is the minimum fix to fix it on Linux >> > as far as I know. >> > >> > If this patch is not the right way to go I would >> > appreciate some guidance on an alternative (but low cost) >> > implementation. Note I don't have capacity for any overly >> > complicated solutions. >> >> The patch looks generally ok, but you are never giving back pages to the > > It gives back pages, just not virtual address space. But I guess that is > what you meant. > > On the other hand this patch can actually give you more virtual > address space when you need large regions (>2 pages or so). > The reason is that the old allocation pattern fragments the whole > address space badly and only leaves these small holes. With the madvise > patch that does not happen, ggc is all in a compacted chunk.
Sure, but we do compete with the glibc heap with virtual memory usage (I wonder if GGC should simply use malloc/free ...). So I am worried that we run out of address space earlier this way. But I guess we can revisit this when we run into actual problems ... >> system, and as we have other memory allocations that do not use the >> ggc pools you drain virtual memory on 32bit hosts. Is any other patch >> in this series compensating for it? If not I'd say we should munmap the >> pages when a full mapped range (2MB) is free. Can you rename > > I wrote such a patch initially, but ran into various problems, so > I dropped it from the series. I can revisit it. Yes, please revisit it. It should be as simple as scanning for a large chunk in free_pages I suppose. >> 'unmapped' to 'discarded' please? That would be less confusing. > > Ok I can do that. > > Was that an approval? Ok with the rename. Thanks, Richard. > -Andi >
