Hi Marko, On Sat, Sep 9, 2017 at 5:31 PM, Marko Rauhamaa <ma...@pacujo.net> wrote:
> Linas Vepstas <linasveps...@gmail.com>: > > So if you used GC_malloc_atomic() in your code, then gc will NOT scan > > that region for pointers. guile-2.2 does this correctly for strings (I > > checked) because strings will never contain pointers. I have not > > checked other uses. > > The question about mmap(2) is addressed more directly by the README > under <URL: https://github.com/ivmai/bdwgc>: > > Any objects not intended to be collected must be pointed to either > from other such accessible objects, or from the registers, stack, > data, or statically allocated bss segments. [...] > > WARNING: pointers inside memory allocated by the standard malloc are > not seen by the garbage collector. Thus objects pointed to only from > such a region may be prematurely deallocated. It is thus suggested > that the standard malloc be used only for memory regions, such as I/O > buffers, that are guaranteed not to contain pointers to garbage > collectible memory. > > [...] > > WARNING: the collector does not guarantee to scan thread-local > storage (e.g. of the kind accessed with pthread_getspecific). The > collector does scan thread stacks > > Now, the question is, can you make your multigigabyte allocation go into > these excluded memory segments? Are you still hit by the pathological GC > behavior you reported? > What, my app, specifically? Uh yeah. All of my c++ objects go through plain-old malloc and should be 100% invisible to guile and to bdwgc and that's perfect. I do have a layer where guile interacts with the C++ code, and all the various bits and pieces are correctly declared everywhere. That code is about 8-10 years old, its been maintained all that time, its been in use all that time, and works without issues. "works without issues" means this: A typical run for me uses some 50-100 threads, maybe 1/2 of these in guile. Due to lock contention, in practice only 3 to 10 of these threads ever get scheduled, and this is fine, and not unexpected. My algos are the opposite of "embrassingly parallel", so low parallelism is expected. Each processing run goes for a few days to weeks or over a month, uses 2 to 50GB RAM, does not leak memory, does not crash, its stable, predictable, does what its supposed to do, terminates cleanly. It does sometimes run much slower than expected (about 1/2x or 1/4x) and I don't know why. I don't usually monitor GC, but when I do, it seems that a lot of cpu time gets wasted there. Sometimes other people also notice this, bitch at me, and propose silly solutions. I've been ignoring that as lower-priority. Only now it's risen up and is biting hard, and I don't understand how or why gc gets triggered in guile. For my app, it seems that it is running far, far too often, and is severely slowing/preventing forward progress. --linas > > > Marko > -- *"The problem is not that artificial intelligence will get too smart and take over the world," computer scientist Pedro Domingos writes, "the problem is that it's too stupid and already has." *
