709045 - memstats is reporting non-believable Overhead

Status: RESOLVED WONTFIX

(Tamarin Graveyard :: Garbage Collection (mmGC), defect)

Description

[Felix S. Klock II [:pnkfelix, :fklock]]

Attachment: derivative of benchmark claimed to show memory regression

For the attached benchmark I'm playing with, avmshell -memstats issues data like:

TR-serrano: Overhead 790928 bytes (772 kb)

TR-mozilla: Overhead 4294502424 bytes (4294966842 kb)

Comment 1

[Felix S. Klock II [:pnkfelix, :fklock]]

(The observation from comment 0 is true for both 32- and 64-bit release builds of avmshell on Mac OS X.)

Comment 2

[Felix S. Klock II [:pnkfelix, :fklock]]

Appeared to have been injected by the following changeset, attached to Bug 659281, comment 5

  changeset: 6342:d7646afb9d65
  user:      Lars T Hansen <[e-mail]>
  summary:   Fix 659281 - Do some accounting on demand, not for every alloc and free (r=treilly)
  
  http://hg.mozilla.org/tamarin-redux/rev/d7646afb9d65

Comment 3

[Felix S. Klock II [:pnkfelix, :fklock]]

(it looks like the problem is that code introduced confusion about the units of the quantities involved... at some points we need to scale by the m_itemSize for the GCAlloc, and at some points we need to scale by the m_itemsPerBlock for the GCAlloc, and I'm pretty sure that we're either missing or have an extra one of the m_itemsPerBlock mixed in, depending on whether the bug is with the calculation of maxAlloc or with the calculation of numAlloc.)

Comment 4

[Felix S. Klock II [:pnkfelix, :fklock]]

(this bug probably only matters for memstats; as far as I can tell so far, it is maxAlloc that is miscalculated, and maxAlloc is only used by the memstats dumping code.  In particular, the bug is not necessarily causing policy failures, unless there is correlated unit-confusion elsewhere.)

Comment 5

[Tamarin Bot]

changeset: 6778:ba9ef082e6a8
user:      Felix S Klock II <[e-mail]>
summary:   Bug 709045: fix with driveby sanity-assert (r=fklockii).

http://hg.mozilla.org/tamarin-redux/rev/ba9ef082e6a8

Comment 6

[Sylvestre Ledru [:Sylvestre]]

Tamarin isn't maintained anymore. WONTFIX remaining bugs.