git: libc - Remove optimization that breaks malloc_usable_size() use cases

[Matthew Dillon]

commit b4510a66558751a074cf6a0f30977b8639ce856f
Author: Matthew Dillon <dillon at apollo.backplane.com>
Date:   Mon Sep 7 14:02:42 2026 -0700

    libc - Remove optimization that breaks malloc_usable_size() use cases
    
    * The malloc implementation had an optimization meant to aid realloc()s
      whereby unused portions of large memory blocks could be munmap()d.
    
      However, lots of code uses the space returned by malloc_usable_size()
      without calling realloc() to notify libc that additional space is being
      used.  Leading to segmentation faults.
    
    * Original proposed solution to make malloc_usable_size() aware of a
      prior munmap optimization does not completely fix the problem as excess
      space may be unmapped after such calls as well as before.
    
    * Removing the optimization and letting the pager deal with any actually-dead
      excess space is the only option.  So that is what we do.
    
    Reported-by: Several people

Summary of changes:
 lib/libc/stdlib/nmalloc.c | 40 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 38 insertions(+), 2 deletions(-)

http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/b4510a66558751a074cf6a0f30977b8639ce856f


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