In stability-land we're starting to see some "interesting" problems
relating to virtual memory usage in Firefox on Windows.
See bug 875030 for information that led me along this path. In this
case, the user has plenty of memory (according to Windows) and is still
failing to allocate moderate-size graphics buffers (1-2MB). This has
very similar symptoms to a bunch of other crashes that we've been seeing
in low volume over the past few years. This has become more urgent
because low-memory crashes often fail to report good crash reports
(because taking a crash reporting minidump requires some allocation on
Windows).
Fortunately on Windows, the minidump contains complete information about
the access and commit state of every process page. I have created a
visualizer for this information here:
http://people.mozilla.com/~bsmedberg/graphical-minidump-memoryinfo/
In this case, the crash report shows "Available Virtual Memory" as
303558656, but in fact the largest contiguous block of available VM is 64k.
There are a couple problems here:
1) early in the memory info, there appears to be a common pattern of a
committed block and then 15 free blocks.
2) later on, there appear to be a large number of 8.7MB allocated blocks
which are mapped memory. The minidump does not appear tell me any more
about the mapping, whether it is a file mapping, or named or anonymous
shared memory.
3) The user (who can reproduce this reliably) reports that disabling the
nviia graphics card and switching to integrated graphics on their laptop
solves the issue.
I think we need to urgently solve the most common crash issue by making
more graphics allocations fallible (bug 829954), and I think Bas is
working on that. But that's only going to cause Firefox behave weirdly
instead of crashing.
Either our code or the ATI driver is leaking mapped memory references in
a way that chews up VM space without actually using memory. We need to
figure out why and fix our work around the problem. I'm hoping that one
of you on the "To" of this email may be able to help figure out a way to
either patch Firefox or run an external debugging tool which can help
record information about the stacks when these mappings are typically
created and destroyed, and help create a detailed understanding of the
problem so that we can either fix our code or hand the problem to the
nvidia developers with the most reproducible/detailed report possible.
--BDS
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