Repeated allocation of very large block

Alan_Cheney · February 14, 2020, 2:03am

Have other people seen this warning in the shell?

GC Warning: Repeated allocation of very large block (appr. size 737280):
May lead to memory leak and poor performance.

I see it suspiciously lurking around crashes and UI slowness, but have no idea what is causing it, or if there’s anything I can do about it. Any ideas?

tannaz · February 15, 2020, 1:19am

Hi Alan! Welcome to the forums

I did a search through our ticket history, and that message has come up only a small handful of times over the years, and always in relation to RV. (And surprisingly, Googling the warning message only brings up two results!)

You mention that it’s showing up in your shell, and mention that you are guessing there’s a connection to UI slowness, but which UI are you referring to? Is this a shell you’re launching RV from? Or some other Shotgun-related UI?

Alan_Cheney · February 15, 2020, 1:28am

Hi Tannaz -
Thanks for responding. Sorry, I wasn’t thinking about the forum being bigger than just RV so I didn’t specify well enough! Yes, the shell that we launch rv from is where I see that message, and the RV UI (or possibly our plugins inside RV) are what sometimes gets bogged down.

tannaz · February 15, 2020, 1:30am

No worries! These forums have some windy roads to navigate

I’ve moved this post to the RV category to ensure the right eyes see it.

desruie · February 18, 2020, 2:12pm

This warning comes from the Boehm Garbage Collector, an open source GC used by the Mu language.

github.com

ivmai/bdwgc/blob/d78fff159996fd790e02c42971bd06fe9dd34aaa/allchblk.c#L739


        /* We must now allocate thishbp, since it may     */
        /* be on the wrong free list.                     */
    }
  }
} else if (size_needed > (signed_word)BL_LIMIT
           && orig_avail - size_needed
              > (signed_word)BL_LIMIT) {
  /* Punt, since anything else risks unreasonable heap growth. */
  if (++GC_large_alloc_warn_suppressed
      >= GC_large_alloc_warn_interval) {
    WARN("Repeated allocation of very large block "
         "(appr. size %" WARN_PRIdPTR "):\n"
         "\tMay lead to memory leak and poor performance\n",
         size_needed);
    GC_large_alloc_warn_suppressed = 0;
  }
  size_avail = orig_avail;
} else if (size_avail == 0
           && size_needed == (signed_word)HBLKSIZE
           && IS_MAPPED(hhdr)) {
  if (!GC_find_leak) {

If you have custom Mu code in your workflow, you might want to look for large allocations. I am not 100% sure this warning means that there are leaks, by looking at the GC code, this seems to detect when there are multiple large memory allocations (>5 by default and we’re not changing it in RV).

I hope this helps.

Eric

Alan_Cheney · February 18, 2020, 4:51pm

Thanks for sending that, Eric. We don’t have much custom Mu code, and it’s mostly just for custom overlays and such, so there shouldn’t be any large allocations in it. Is it possible that native RV (Mu) code is hitting this warning, like in RV API code that our code calls, such as loading very large files?

Thanks,
Alan