701210 - nsTArray::SizeOf() should use malloc_usable_size

Status: RESOLVED FIXED

(Core :: XPCOM, defect)

Description

[Justin Lebar (not reading bugmail)]

// @return The amount of memory taken used by this nsTArray, not including
  // sizeof(this)
  size_t SizeOf() const {
    return this->UsesAutoArrayBuffer() ?
      0 : this->Capacity() * sizeof(elem_type) + sizeof(*this->Hdr());
  }

This isn't as bad as it looks, because the capacity is chosen so that the capacity plus the header is a power of 2.  But there can be a few bytes of slop in there, and a call to Compact() will mess this calculation up.

Comment 1

[Justin Lebar (not reading bugmail)]

Attachment: Patch v1

Comment 2

[Justin Lebar (not reading bugmail)]

Thanks, roc.

https://hg.mozilla.org/integration/mozilla-inbound/rev/71ca2fa34ca9

Comment 3

[Marco Bonardo [:mak]]

https://hg.mozilla.org/mozilla-central/rev/71ca2fa34ca9

Comment 4

[Justin Lebar (not reading bugmail)]

OOC, does this show up as a +1/-1 in the weekly MemShrink report?

Comment 5

[Nicholas Nethercote [inactive]]

(In reply to Justin Lebar [:jlebar] from comment #4)
> OOC, does this show up as a +1/-1 in the weekly MemShrink report?

No.  I record the open P1/P2/P3/U bug numbers each week, and diff with the previous week.  A bug that's fixed in this timeframe won't be present in either snapshot, so it won't be counted.