To whom it may concern.

Commenting out line 25 of win32\VMem.h fixes the problem of wildly excessive page faults, that are causing a quadratic slowdown on memory allocations under some circumstances.

/* vmem.h
 *
 * (c) 1999 Microsoft Corporation. All rights reserved.
 * Portions (c) 1999 ActiveState Tool Corp, http://www.ActiveState.com
+/
 *
 *    You may distribute under the terms of either the GNU General Pub
+lic
 *    License or the Artistic License, as specified in the README file
+.
 *
 * Options:
 *
 * Defining _USE_MSVCRT_MEM_ALLOC will cause all memory allocations
 * to be forwarded to MSVCRT.DLL. Defining _USE_LINKED_LIST as well wi
+ll
 * track all allocations in a doubly linked list, so that the host can
 * free all memory allocated when it goes away.
 * If _USE_MSVCRT_MEM_ALLOC is not defined then Knuth's boundary tag a
+lgorithm
 * is used; defining _USE_BUDDY_BLOCKS will use Knuth's algorithm R
 * (Buddy system reservation)
 *
 */

#ifndef ___VMEM_H_INC___
#define ___VMEM_H_INC___

#ifndef UNDER_CE
//#define _USE_MSVCRT_MEM_ALLOC // <<<<<<<<<< HERE
#endif
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With this fix, the OP snippet that takes 32+ seconds to run, now takes just 0.4 seconds:

Update: Should'a mentioned 37,000 page faults instead of 5,7 million. Memory consumption the same in both cases.

.\perl -MTime::HiRes=time -wE"my $t=time; my @a=map $_,map $_,1..1e6;s
+ay time-$t;<>"
0.392155885696411
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I've tried to reason about the possible consequences of this change, but get lost in the layers upon layers of conditional redefinition, redirection and misdirection in the perl sources. It doesn't appear to cause any additional test suite failures, but then I seriously doubt if the appropriate circumstances are being tested anywhere.