git rev-list | git cherry-pick --stdin is leaky

Hi,

I'm running git rev-list | git cherry-pick --stdin on a range of about
300 commits. Eventually the chery-pick dies with:

    error: cannot fork() for commit: Cannot allocate memory

Running valgrind shows me that the tree traversal code is leaking
gigabytes of memory (particularly unpack_callback). Since cherry-pick is
a very long running process all these allocations are never freed and
eventually I run out of memory. Attached is the valgrind output. The
worst offender and summary is:

==7986== 938,956,692 (929,961,582 direct, 8,995,110 indirect) bytes in 7,765,439 blocks are definitely lost in loss record 257 of 257
==7986==    at 0x4C267CC: calloc (vg_replace_malloc.c:467)
==7986==    by 0x4FAF57: xcalloc (wrapper.c:119)
==7986==    by 0x4F5281: unpack_callback (unpack-trees.c:539)
==7986==    by 0x4F40E5: traverse_trees (tree-walk.c:407)
==7986==    by 0x4F586C: unpack_callback (unpack-trees.c:467)
==7986==    by 0x4F40E5: traverse_trees (tree-walk.c:407)
==7986==    by 0x4F586C: unpack_callback (unpack-trees.c:467)
==7986==    by 0x4F40E5: traverse_trees (tree-walk.c:407)
==7986==    by 0x4F586C: unpack_callback (unpack-trees.c:467)
==7986==    by 0x4F40E5: traverse_trees (tree-walk.c:407)
==7986==    by 0x4F586C: unpack_callback (unpack-trees.c:467)
==7986==    by 0x4F40E5: traverse_trees (tree-walk.c:407)
==7986==
==7986== LEAK SUMMARY:
==7986==    definitely lost: 2,514,117,692 bytes in 21,210,861 blocks
==7986==    indirectly lost: 885,481,947 bytes in 10,165,801 blocks
==7986==      possibly lost: 650,712,395 bytes in 6,014,309 blocks
==7986==    still reachable: 7,734,870 bytes in 47,794 blocks
==7986==         suppressed: 0 bytes in 0 blocks

This is against recent git.git
(89740333e8d398f1da701e9023675321bbb9a85b). A workaround is to limit the
amount of commits per cherry-pick invocation, but can we somehow fix the
leaks?

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