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aclements opened this issue Jul 31, 2017 · 2 comments
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runtime: cherry-pick CLs 51713 and 51714 #21234

aclements opened this issue Jul 31, 2017 · 2 comments
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@aclements aclements added this to the Go1.9 milestone Jul 31, 2017
@aclements aclements self-assigned this Jul 31, 2017
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Change https://golang.org/cl/52190 mentions this issue: [release-branch.go1.9] runtime: fall back to small mmaps if we fail to grow reservation

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Change https://golang.org/cl/52191 mentions this issue: [release-branch.go1.9] runtime: map bitmap and spans during heap initialization

gopherbot pushed a commit that referenced this issue Jul 31, 2017
@aclements
[release-branch.go1.9] runtime: fall back to small mmaps if we fail t…
1a6d87d 
…o grow reservation

Right now, if it's possible to grow the arena reservation but
mheap.sysAlloc fails to get 256MB more of memory, it simply fails.
However, on 32-bit we have a fallback path that uses much smaller
mmaps that could take in this situation, but fail to.

This commit fixes mheap.sysAlloc to use a common failure path in case
it can't grow the reservation. On 32-bit, this path includes the
fallback.

Ideally, mheap.sysAlloc would attempt smaller reservation growths
first, but taking the fallback path is a simple change for Go 1.9.

Updates #21044 (fixes one of two issues).

Cherry-pick of CL 51713. Updates #21234.

Change-Id: I1e0035ffba986c3551479d5742809e43da5e7c73
Reviewed-on: https://go-review.googlesource.com/52190
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
gopherbot pushed a commit that referenced this issue Jul 31, 2017
@aclements
[release-branch.go1.9] runtime: map bitmap and spans during heap init…
196492a 
…ialization

We lazily map the bitmap and spans areas as the heap grows. However,
right now we're very slightly too lazy. Specifically, the following
can happen on 32-bit:

1. mallocinit fails to allocate any heap arena, so
   arena_used == arena_alloc == arena_end == bitmap.

2. There's less than 256MB between the end of the bitmap mapping and
   the next mapping.

3. On the first allocation, mheap.sysAlloc sees that there's not
   enough room in [arena_alloc, arena_end) because there's no room at
   all. It gets a 256MB mapping from somewhere *lower* in the address
   space than arena_used and sets arena_alloc and arena_end to this
   hole.

4. Since the new arena_alloc is lower than arena_used, mheap.sysAlloc
   doesn't bother to call mheap.setArenaUsed, so we still don't have a
   bitmap mapping or a spans array mapping.

5. mheap.grow, which called mheap.sysAlloc, attempts to fill in the
   spans array and crashes.

Fix this by mapping the metadata regions for the initial arena_used
when the heap is initialized, rather than trying to wait for an
allocation. This maintains the intended invariant that the structures
are always mapped for [arena_start, arena_used).

Fixes #21044.

Cherry-pick of CL 51714. Fixes #21234.

Change-Id: I4422375a6e234b9f979d22135fc63ae3395946b0
Reviewed-on: https://go-review.googlesource.com/52191
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
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