win2k/cygwin cannot handle even moderately sized packs

For me, it fails even on 332Mb pack:

$ git reset --hard 61bb7fcb
fatal: packfile .git/objects/pack/pack-ad37...pack cannot be mapped.

Instrumenting the code reveals that it fails on 348876870 bytes.
Strangely enough, a cygwin program which just reads that pack
many times without freeing the mem goes up to 1395507480 (1330Mb).

If I replace the malloc (cygwin) with native VirtualAlloc(MEM_COMMIT)
it reports that "Not enough storage is available to process this command",
which is just ENOMEM, I think.

This is a 2Gb machine, with almost 1.3Gb free, so I'm a bit confused,
what could here go wrong (besides what already is wrong).