On 12.11.2014 19:01, Iain Buclaw wrote:
On Tuesday, 11 November 2014 at 20:20:26 UTC, Rainer Schuetze wrote:
The GC allocates pools of memory in increasing size. It starts with 1
MB, then adds 3MB for every new pool. (Numbers might be slightly
different depending on the druntime version). These pools are then
used to service any allocation request.
gc_minimize can only return memory to the system if all the allocation
in a pool are collected, which is very unlikely.
I'm aware of roughly how the gc grows. But it seems an unlikely
scenario to have 200MB worth of 3MB pools with at least one object in each.
The pools have sizes 1, 4, 7, 10, 14, 17, 20, 23, 26, 29 and 33 MB, so
only 11 pools overall. It will depend on your allocation patterns if
they hold at least one object though.
And if it did get to that state, the next question would be, how? I
could say, I'd expect that if a large number of requests came in all at
once, but I would have been prompted by this in the network graphs.
The only reason I see would be fragmentation, but that should only
happen if you have bad allocation patterns for large (>2k) memory
blocks, e.g. a large growing array with allocation of smaller (but still
> 2k) size inbetween that are never collected.
When I noticed gc_stats with an informative *experimental* warning, I
thought "lets just run it anyway and see what happens"... SEGV.
Wonderful.
I suspect calling gc_stats from the debugger is "experimental" because
it returns a struct. With a bit of casting, you might by able to call
"_gc.getStats( *cast(GCStats*)some_mem_adr );" instead.
No, that is not the reason. More like the iterative scan may be
unsafe. I should have looked closer at the backtrace / memory location
that was violated (I was in a hurry to get the site back up), but a more
likely cause of the SEGV is that one of the pools in gcx.pooltable[n] or
pages in pool.pagetable[n] was pointing to a free'd, stomped, or null
location.
I have used it without problems in the past when working on the GC.
Maybe you have stopped the application during a collection?
