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runtime: mheap.busyList use unproper len when return list from h.busy #18944

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zhaozhiqianghw opened this issue Feb 5, 2017 · 4 comments

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commented Feb 5, 2017

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

1.7.4

What operating system and processor architecture are you using (go env)?

linux amd64

The definition of mheap.busyList locate in mheap.go:943 as followed:

func (h *mheap) busyList(npages uintptr) *mSpanList {
if npages < uintptr(len(h.free)) {
return &h.busy[npages]
}
return &h.busylarge
}

When check if it can return the busy list using "len(free)", I think it's not proper.
Although the current version of Go set the same lenght of h.free and h.busy, it's different.

The same puzzle occurs at the definition of mheap.alloc_m @ mheap.go:592:
if large {
memstats.heap_objects++
atomic.Xadd64(&memstats.heap_live, int64(npage<<_PageShift))
// Swept spans are at the end of lists.
if s.npages < uintptr(len(h.free)) {
h.busy[s.npages].insertBack(s)
} else {
h.busylarge.insertBack(s)
}
}

So it's a mistake, or it's some design.

@ianlancetaylor ianlancetaylor added this to the Go1.9 milestone Feb 5, 2017

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commented Feb 5, 2017

@aclements

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commented Feb 5, 2017

This is a little obtuse, but I wouldn't call it a bug. The free and busy lists must have the same length since we move short spans back and forth between these two lists.

It would be perfectly reasonable to change both of these to len(h.busy).

@zhaozhiqianghw

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commented Feb 5, 2017

Yes, this is not a bug. It's better for reading.

@gopherbot

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commented Feb 6, 2017

CL https://golang.org/cl/36354 mentions this issue.

@gopherbot gopherbot closed this in 77f64c5 Mar 3, 2017

@golang golang locked and limited conversation to collaborators Mar 3, 2018

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