Performance optimization in av::fixup - use buffered IO, not mapped file

Daniel Colascione
Wed Dec 12 01:06:00 GMT 2012

On 12/10/2012 7:51 PM, Daniel Colascione wrote:
> The key to generating a binary that repros the problem is to unexec emacs, then
> try to repro with that generated binary, not a copy of it.

The real explanation is a lot simpler: the binary is sparse. When you create a
file mapping object for a sparse file, Windows discards all cached pages for
that file. It makes sense that compilers (and Emacs unexec) would create sparse
files as they seek around inside their outputs.

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