Request for review (S): 7103665 HeapWord*ParallelScavengeHeap::failed_mem_allocate(unsigned long, bool)+0x97

[Jon Masamitsu]

Bengt,

Is it correct that there is still the possibility that during the final
iteration of the loop to do the filling, that the space to be filled
can be too small to fit an object?  I note the assertion

>    98           assert(words_to_fill>= CollectedHeap::min_fill_size(),
>    99             err_msg("Remaining siz ("SIZE_FORMAT ") is too small to fill (based on " SIZE_FORMAT " and " SIZE_FORMAT ")",
>   100             words_to_fill, words_left_to_fill, CollectedHeap::filler_array_max_size()));

You could fix that by checking for the situation in the next to last
iteration and shortening the filler for the next to last iteration?

Also a question below.


On 3/23/2012 5:56 AM, Bengt Rutisson wrote:
>
> Hi all,
>
> Could I have a couple of reviews for this change? This is on the 
> critical-watch list for hs23, so it would be great if I could get some 
> reviews already today.
>
> http://cr.openjdk.java.net/~brutisso/7103665/webrev.00/
>
> Some background:
>
> There are two problems that this fix solves:
>
> (1) When we run with -XX:+UseNUMA we have to make the heap parsable 
> since we leave some holes in the heap. We do this by faking Integer 
> arrays in those places. However, on a large heap those holes can be 
> larger than what can be covered by a single Integer array. The fix is 
> to allocate several arrays in those cases.
>
> The easy fix would have been to call 
> CollectedHeap::fill_with_objects() instead of 
> CollectedHeap::fill_with_object(). Note the extra "s" in the method 
> name. But MutableNUMASpace::ensure_parsability(), where the change is 
> needed, need to know about all the objects that are allocated so I saw 
> no better solution than to implement my own loop. Any ideas on how I 
> could re-use fill_with_objects() instead are welcome.

Do you need to know all the objects that are allocated so that you can
do the invalid region detection?

  113             if (crossing_start != crossing_end) {
  114               // If object header crossed a small page boundary we 
mark the area
  115               // as invalid rounding it to a page_size().


Jon
>
> (2) CollectedHeap::_filler_array_max_size should be the maximum size 
> that can be covered by a fake Integer array. This value is in words, 
> but since the word size is different on different platforms but the 
> Integer size is always the same we need to convert between word and 
> sizeof(jint) at some point. Unfortunately we do the conversion in the 
> wrong direction, which means that on 64 bit platforms we end up with a 
> max size that is 4 times larger than intended. This in turn makes us 
> overflow an int when we convert from a word size to the length of the 
> array that we are setting up.
>
> Here is the code that overflows:
>
>  328 void
>  329 CollectedHeap::fill_with_array(HeapWord* start, size_t words, 
> bool zap)
>  330 {
>  331   assert(words >= filler_array_min_size(), "too small for an 
> array");
>  332   assert(words <= filler_array_max_size(), "too big for a single 
> object");
>  333
>  334   const size_t payload_size = words - filler_array_hdr_size();
>  335   const size_t len = payload_size * HeapWordSize / sizeof(jint);
>  336
>  337   // Set the length first for concurrent GC.
>  338   ((arrayOop)start)->set_length((int)len);
>  339   post_allocation_setup_common(Universe::intArrayKlassObj(), 
> start, words);
>  340   DEBUG_ONLY(zap_filler_array(start, words, zap);)
>  341 }
>
> If filler_array_max_size() on line 332, which returns 
> CollectedHeap::_filler_array_max_size, has a too large value we will 
> overflow the int conversation on line 338.
>
> Testing:
> This fix solves the issue that was found in the reproducer that I 
> could set up on a Linux x64 machine. I have asked the one who 
> initially reported the issue to run on their Solaris amd64 setup. I 
> will also try to set up a reproducer on a Solaris machine.
>
> I also ran the fix through JPRT. It did not fail, but there are no 
> NUMA tests in there as far as I know. But the change for issue (2) was 
> hopefully tested.
>
> Thanks,
> Bengt