Here's an example where we allocate a large (4K) stack: >>> bt #0 allocateMightFail (cap=0x7f366808cfc0 <MainCapability>, n=4096) at rts/sm/Storage.c:876 #1 0x00007f3667e4a85d in allocate (cap=0x7f366808cfc0 <MainCapability>, n=4096) at rts/sm/Storage.c:849 #2 0x00007f3667e16f46 in threadStackOverflow (cap=0x7f366808cfc0 <MainCapability>, tso=0x4200152a68) at rts/Threads.c:600 #3 0x00007f3667e12a64 in schedule (initialCapability=0x7f366808cfc0 <MainCapability>, task=0x78c970) at rts/Schedule.c:520 #4 0x00007f3667e1215f in scheduleWaitThread (tso=0x4200105388, ret=0x0, pcap=0x7ffef40dce78) at rts/Schedule.c:2533 #5 0x00007f3667e25685 in rts_evalLazyIO (cap=0x7ffef40dce78, p=0x736ef8, ret=0x0) at rts/RtsAPI.c:530 #6 0x00007f3667e25f7a in hs_main (argc=16, argv=0x7ffef40dd0a8, main_closure=0x736ef8, rts_config=...) t rts/RtsMain.c:72 #7 0x00000000004f738f in main ()
This is based on an old tree so source locations may not be correct, it's this code in threadStackOverflow(): // Charge the current thread for allocating stack. Stack usage is // non-deterministic, because the chunk boundaries might vary from // run to run, but accounting for this is better than not // accounting for it, since a deep recursion will otherwise not be // subject to allocation limits. cap->r.rCurrentTSO = tso; new_stack = (StgStack*) allocate(cap, chunk_size); cap->r.rCurrentTSO = NULL; SET_HDR(new_stack, &stg_STACK_info, old_stack->header.prof.ccs); TICK_ALLOC_STACK(chunk_size); Ömer Ömer Sinan Ağacan <omeraga...@gmail.com>, 21 Haz 2018 Per, 13:42 tarihinde şunu yazdı: > > > Large objects can only be primitive objects, like MUT_ARR_PTRS, allocated by > > the RTS, and none of these have SRTs. > > Is is not possible to allocate a large STACK? I'm currently observing this in > gdb: > > >>> call *Bdescr(0x4200ec9000) > $2 = { > start = 0x4200ec9000, > free = 0x4200ed1000, > link = 0x4200100e80, > u = { > back = 0x4200103980, > bitmap = 0x4200103980, > scan = 0x4200103980 > }, > gen = 0x77b4b8, > gen_no = 1, > dest_no = 1, > node = 0, > flags = 1027, <-- BF_LARGE | BF_EVACUTED | ... > blocks = 8, > _padding = {[0] = 0, [1] = 0, [2] = 0} > } > > >>> call printClosure(0x4200ec9000) > 0x4200ec9000: STACK > > >>> call checkClosure(0x4200ec9000) > $3 = 4096 -- makes sense, larger than 3277 bytes > > So I have a large STACK object, and STACKs can refer to static objects. But > when we scavenge this object we don't scavenge its SRTs because we use > scavenge_one(). This seems wrong to me. > > Ömer > > Simon Marlow <marlo...@gmail.com>, 20 Haz 2018 Çar, 14:32 tarihinde şunu > yazdı: > > > > Interesting point. I don't think there are any large objects with SRTs, but > > we should document the invariant because we're relying on it. > > > > Large objects can only be primitive objects, like MUT_ARR_PTRS, allocated > > by the RTS, and none of these have SRTs. > > > > We did have plans to allocate memory for large dynamic objects using > > `allocate()` from compiled code, in which case we could have large objects > > that could be THUNK, FUN, etc. and could have an SRT, in which case we > > would need to revisit this. You might want to take a look at Note [big > > objects] in GCUtils.c, which is relevant here. > > > > Cheers > > Simon > > > > > > On 20 June 2018 at 09:20, Ömer Sinan Ağacan <omeraga...@gmail.com> wrote: > >> > >> Hi Simon, > >> > >> I'm confused about this code again. You said > >> > >> > scavenge_one() is only used for a non-major collection, where we aren't > >> > traversing SRTs. > >> > >> But I think this is not true; scavenge_one() is also used to scavenge large > >> objects (in scavenge_large()), which are scavenged even in major GCs. So it > >> seems like we never really scavenge SRTs of large objects. This doesn't > >> look > >> right to me. Am I missing anything? Can large objects not refer to static > >> objects? > >> > >> Thanks > >> > >> Ömer > >> > >> Ömer Sinan Ağacan <omeraga...@gmail.com>, 2 May 2018 Çar, 09:03 > >> tarihinde şunu yazdı: > >> > > >> > Thanks Simon, this is really helpful. > >> > > >> > > If you look at scavenge_fun_srt() and co, you'll see that they return > >> > > immediately if !major_gc. > >> > > >> > Thanks for pointing this out -- I didn't realize it's returning early > >> > when > >> > !major_gc and this caused a lot of confusion. Now everything makes sense. > >> > > >> > I'll add a note for scavenging SRTs and refer to it in relevant code and > >> > submit > >> > a diff. > >> > > >> > Ömer > >> > > >> > 2018-05-01 22:10 GMT+03:00 Simon Marlow <marlo...@gmail.com>: > >> > > Your explanation is basically right. scavenge_one() is only used for a > >> > > non-major collection, where we aren't traversing SRTs. Admittedly this > >> > > is a > >> > > subtle point that could almost certainly be documented better, I > >> > > probably > >> > > just overlooked it. > >> > > > >> > > More inline: > >> > > > >> > > On 1 May 2018 at 10:26, Ömer Sinan Ağacan <omeraga...@gmail.com> wrote: > >> > >> > >> > >> I have an idea but it doesn't explain everything; > >> > >> > >> > >> SRTs are used to collect CAFs, and CAFs are always added to the oldest > >> > >> generation's mut_list when allocated [1]. > >> > >> > >> > >> When we're scavenging a mut_list we know we're not doing a major GC, > >> > >> and > >> > >> because mut_list of oldest generation has all the newly allocated > >> > >> CAFs, > >> > >> which > >> > >> will be scavenged anyway, no need to scavenge SRTs for those. > >> > >> > >> > >> Also, static objects are always evacuated to the oldest gen [2], so > >> > >> any > >> > >> CAFs > >> > >> that are alive but not in the mut_list of the oldest gen will stay > >> > >> alive > >> > >> after > >> > >> a non-major GC, again no need to scavenge SRTs to keep these alive. > >> > >> > >> > >> This also explains why it's OK to not collect static objects (and not > >> > >> treat > >> > >> them as roots) in non-major GCs. > >> > >> > >> > >> However this doesn't explain > >> > >> > >> > >> - Why it's OK to scavenge large objects with scavenge_one(). > >> > > > >> > > > >> > > I don't understand - perhaps you could elaborate on why you think it > >> > > might > >> > > not be OK? Large objects are treated exactly the same as small objects > >> > > with > >> > > respect to their lifetimes. > >> > > > >> > >> > >> > >> - Why we scavenge SRTs in non-major collections in other places (e.g. > >> > >> scavenge_block()). > >> > > > >> > > > >> > > If you look at scavenge_fun_srt() and co, you'll see that they return > >> > > immediately if !major_gc. > >> > > > >> > >> > >> > >> Simon, could you say a few words about this? > >> > > > >> > > > >> > > Was that enough words? I have more if necessary :) > >> > > > >> > > Cheers > >> > > Simon > >> > > > >> > > > >> > >> > >> > >> > >> > >> [1]: https://github.com/ghc/ghc/blob/master/rts/sm/Storage.c#L445-L449 > >> > >> [2]: https://github.com/ghc/ghc/blob/master/rts/sm/Scav.c#L1761-L1763 > >> > >> > >> > >> Ömer > >> > >> > >> > >> 2018-03-28 17:49 GMT+03:00 Ben Gamari <b...@well-typed.com>: > >> > >> > Hi Simon, > >> > >> > > >> > >> > I'm a bit confused by scavenge_one; namely it doesn't scavenge > >> > >> > SRTs. It > >> > >> > appears that it is primarily used for remembered set entries but > >> > >> > it's > >> > >> > not at all clear why this means that we can safely ignore SRTs > >> > >> > (e.g. in > >> > >> > the FUN and THUNK cases). > >> > >> > > >> > >> > Can you shed some light on this? > >> > >> > > >> > >> > Cheers, > >> > >> > > >> > >> > - Ben > >> > >> > > >> > >> > _______________________________________________ > >> > >> > ghc-devs mailing list > >> > >> > ghc-devs@haskell.org > >> > >> > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs > >> > >> > > >> > >> _______________________________________________ > >> > >> ghc-devs mailing list > >> > >> ghc-devs@haskell.org > >> > >> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs > >> > > > >> > > > > > > _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs