ReadMemStats accounts for stacks slightly differently than the runtime
does internally. Internally, only stacks allocated by newosproc0 are
accounted in memstats.stacks_sys and other stacks are accounted in
heap_sys. readmemstats_m shuffles the statistics so all stacks are
accounted in StackSys rather than HeapSys.
However, currently, readmemstats_m assumes StackSys will be zero when
it does this shuffle. This was true until commit 6ad33be. If it isn't
(e.g., if something called newosproc0), StackSys+HeapSys will be
different before and after this shuffle, and the Sys sum that was
computed earlier will no longer agree with the sum of its components.
Fix this by making the shuffle in readmemstats_m not assume that
StackSys is zero.
Fixes#10585.
Change-Id: If13991c8de68bd7b85e1b613d3f12b4fd6fd5813
Reviewed-on: https://go-review.googlesource.com/9366
Reviewed-by: Russ Cox <rsc@golang.org>
The motivation is that sysAlloc/Free() currently aren't safe to be
called without a valid G, because arm's xadd64() uses locks that require
a valid G.
The solution here was proposed by Dmitry Vyukov: use xadduintptr()
instead of xadd64(), until arm can support xadd64 on all of its
architectures (not a trivial task for arm).
Change-Id: I250252079357ea2e4360e1235958b1c22051498f
Reviewed-on: https://go-review.googlesource.com/9002
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Currently, we set the heap goal for the next GC cycle using the size
of the marked heap at the end of the current cycle. This can lead to a
bad feedback loop if the mutator is rapidly allocating and releasing
pointers that can significantly bloat heap size.
If the GC were STW, the marked heap size would be exactly the
reachable heap size (call it stwLive). However, in concurrent GC,
marked=stwLive+floatLive, where floatLive is the amount of "floating
garbage": objects that were reachable at some point during the cycle
and were marked, but which are no longer reachable by the end of the
cycle. If the GC cycle is short, then the mutator doesn't have much
time to create floating garbage, so marked≈stwLive. However, if the GC
cycle is long and the mutator is allocating and creating floating
garbage very rapidly, then it's possible that marked≫stwLive. Since
the runtime currently sets the heap goal based on marked, this will
cause it to set a high heap goal. This means that 1) the next GC cycle
will take longer because of the larger heap and 2) the assist ratio
will be low because of the large distance between the trigger and the
goal. The combination of these lets the mutator produce even more
floating garbage in the next cycle, which further exacerbates the
problem.
For example, on the garbage benchmark with GOMAXPROCS=1, this causes
the heap to grow to ~500MB and the garbage collector to retain upwards
of ~300MB of heap, while the true reachable heap size is ~32MB. This,
in turn, causes the GC cycle to take upwards of ~3 seconds.
Fix this bad feedback loop by estimating the true reachable heap size
(stwLive) and using this rather than the marked heap size
(stwLive+floatLive) as the basis for the GC trigger and heap goal.
This breaks the bad feedback loop and causes the mutator to assist
more, which decreases the rate at which it can create floating
garbage. On the same garbage benchmark, this reduces the maximum heap
size to ~73MB, the retained heap to ~40MB, and the duration of the GC
cycle to ~200ms.
Change-Id: I7712244c94240743b266f9eb720c03802799cdd1
Reviewed-on: https://go-review.googlesource.com/9177
Reviewed-by: Rick Hudson <rlh@golang.org>
This implements tracking the scan work ratio of a GC cycle and using
this to estimate the scan work that will be required by the next GC
cycle. Currently this estimate is unused; it will be used to drive
mutator assists.
Change-Id: I8685b59d89cf1d83eddfc9b30d84da4e3a7f4b72
Reviewed-on: https://go-review.googlesource.com/8833
Reviewed-by: Rick Hudson <rlh@golang.org>
Currently there are two main consumers of memstats.heap_alloc:
updatememstats (aka ReadMemStats) and shouldtriggergc.
updatememstats recomputes heap_alloc from the ground up, so we don't
need to keep heap_alloc up to date for it. shouldtriggergc wants to
know how many bytes were marked by the previous GC plus how many bytes
have been allocated since then, but this *isn't* what heap_alloc
tracks. heap_alloc also includes objects that are not marked and
haven't yet been swept.
Introduce a new memstat called heap_live that actually tracks what
shouldtriggergc wants to know and stop keeping heap_alloc up to date.
Unlike heap_alloc, heap_live follows a simple sawtooth that drops
during each mark termination and increases monotonically between GCs.
heap_alloc, on the other hand, has much more complicated behavior: it
may drop during sweep termination, slowly decreases from background
sweeping between GCs, is roughly unaffected by allocation as long as
there are unswept spans (because we sweep and allocate at the same
rate), and may go up after background sweeping is done depending on
the GC trigger.
heap_live simplifies computing next_gc and using it to figure out when
to trigger garbage collection. Currently, we guess next_gc at the end
of a cycle and update it as we sweep and get a better idea of how much
heap was marked. Now, since we're directly tracking how much heap is
marked, we can directly compute next_gc.
This also corrects bugs that could cause us to trigger GC early.
Currently, in any case where sweep termination actually finds spans to
sweep, heap_alloc is an overestimation of live heap, so we'll trigger
GC too early. heap_live, on the other hand, is unaffected by sweeping.
Change-Id: I1f96807b6ed60d4156e8173a8e68745ffc742388
Reviewed-on: https://go-review.googlesource.com/8389
Reviewed-by: Russ Cox <rsc@golang.org>
This tries to clarify that Alloc and HeapAlloc are tied to how much
freeing has been done by the sweeper.
Change-Id: Id8320074bd75de791f39ec01bac99afe28052d02
Reviewed-on: https://go-review.googlesource.com/8354
Reviewed-by: Rick Hudson <rlh@golang.org>
Everything has moved to Go, but comments still refer to .c/.h files.
Fix all of those up, at least for these three directories.
Fixes#10138
Change-Id: Ie5efe89b247841e0b3f82aac5256b2c606ef67dc
Reviewed-on: https://go-review.googlesource.com/7431
Reviewed-by: Russ Cox <rsc@golang.org>
Move code from malloc1.go, malloc2.go, mem.go, mgc0.go into
appropriate locations.
Factor mgc.go into mgc.go, mgcmark.go, mgcsweep.go, mstats.go.
A lot of this code was in certain files because the right place was in
a C file but it was written in Go, or vice versa. This is one step toward
making things actually well-organized again.
Change-Id: I6741deb88a7cfb1c17ffe0bcca3989e10207968f
Reviewed-on: https://go-review.googlesource.com/5300
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Rick Hudson <rlh@golang.org>
