[Bug malloc/14827] New: free() doesn't honor M_TRIM_THRESHOLD

[Bug malloc/14827] New: free() doesn't honor M_TRIM_THRESHOLD

[glibc at iamsergio dot de]

http://sourceware.org/bugzilla/show_bug.cgi?id=14827

             Bug #: 14827
           Summary: free() doesn't honor M_TRIM_THRESHOLD
           Product: glibc
           Version: 2.16
            Status: NEW
          Severity: normal
          Priority: P2
         Component: malloc
        AssignedTo: unassigned@sourceware.org
        ReportedBy: glibc@iamsergio.de
    Classification: Unclassified


Created attachment 6725
  --> http://sourceware.org/bugzilla/attachment.cgi?id=6725
test-case

free() isn't calling brk() to give memory back to the kernel when
M_TRIM_THRESHOLD is passed.

Run the attached test-case.

What it does:
1. Calls malloc() 2800000 times
2. Calls free()   2800000 times
3. pauses, so you can inspect the heap size.

You'll see that the heap size is around 250 MB.

Manually calling malloc_trim(), through gdb, decreases the heap size to 4 K.
----------------------------------------------------

How I measured heap size:

  $ cat /proc/12345/maps | grep heap
    01bc6000-0f180000 rw-p 00000000 00:00 0    [heap]

  $ python
    > (0x0f180000-0x01bc6000) / (1024*1024)
    > 213
    213 Megabytes

  $ top -p12345 # tested with top too
    227m 214m for VIRT and RES respectively

  $ gdb -pid 12345            # Lets attach gdb and call malloc_trim()
    > call malloc_trim(0)

  $ top -p12345
    14492 1076 for VIRT and RES respectively

  $ cat /proc/12345/maps | grep heap
    01bc6000-01bc7000 rw-p 00000000 00:00 0 [heap]

  $ python
    > (0x01bc7000-0x01bc6000) / (1024*1024)
    > 0.00390625 // 4KB 
------------------------------------------------------------
I'm on Linux 3.6.5 with glibc-2.16

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[Bug malloc/14827] free() doesn't honor M_TRIM_THRESHOLD

[glibc at iamsergio dot de]

http://sourceware.org/bugzilla/show_bug.cgi?id=14827

--- Comment #1 from Sérgio Martins <glibc at iamsergio dot de> 2012-11-16 17:03:23 UTC ---
This seems to be caused due to the "fastbins" features.

free() doesn't trim fastbins because the malloc() was less than M_MXFAST.

But there really should be a limit to the number of fastbins that we keep
around.

In KDE we've seen 600MB of memory being freed after attaching gdb and calling
malloc_trim(0)

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[Bug malloc/14827] free() doesn't honor M_TRIM_THRESHOLD

[mail at milianw dot de]

http://sourceware.org/bugzilla/show_bug.cgi?id=14827

Milian Wolff <mail at milianw dot de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mail at milianw dot de

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[Bug malloc/14827] free() doesn't honor M_TRIM_THRESHOLD

[mail at milianw dot de]

http://sourceware.org/bugzilla/show_bug.cgi?id=14827

--- Comment #2 from Milian Wolff <mail at milianw dot de> 2012-11-19 17:04:08 UTC ---
I can reproduce this issue and think its also an issue for KDevelop and similar
apps. What else is needed to improve the situation here?

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[Bug malloc/14827] free() doesn't honor M_TRIM_THRESHOLD

[bharath.vegito at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=14827

Bharath H S <bharath.vegito at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bharath.vegito at gmail dot com

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[Bug malloc/14827] free() doesn't honor M_TRIM_THRESHOLD

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=14827

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |security-

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[Bug malloc/14827] free() doesn't honor M_TRIM_THRESHOLD

[carlos at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=14827

Carlos O'Donell <carlos at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://bugzilla.redhat.com
                   |                            |/show_bug.cgi?id=921676

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