SICSA2011

Since 29.Aug till 1.Sep there was a small summer school at St.Andrews, Scotland: Advanced techniques in computer algebra systems development.

It was about CAS internals, memory management/garbage collection, parallelization, thread-safety etc.

In particular, here is my talk about the Singular memory management library: omalloc.

Singular memory

As you probably know: Singular uses omalloc by Olaf Bachmann. It allows fast allocation of memory blocks of the same size.

Just a while ago we released new Singular: 3-1-2. Among other stuff it has the following experimental (and undocumented) feature: one can print out omalloc status (every single memory-related number) AND will try to test omalloc consistency.

In order to call it - simply type:

system("omMemoryTest");

Here follows its output on my machine:

> system("omMemoryTest");

[om_Info]: 
 MaxBytesSystem         :     794624 
 CurrentBytesSystem     :     794624 
 MaxBytesSbrk           :     270336 
 CurrentBytesSbrk       :     270336 
 MaxBytesMmap           :     524288 
 CurrentBytesMmap       :     524288 
 UsedBytes              :     156976 
 AvailBytes             :     493880 
 UsedBytesMalloc        :     126568 
 AvailBytesMalloc       :          0 
 MaxBytesFromMalloc     :     126568 
 CurrentBytesFromMalloc :     126568 
 MaxBytesFromValloc     :     524288 
 CurrentBytesFromValloc :     524288 
 UsedBytesFromValloc    :      30408 
 AvailBytesFromValloc   :     493880 
 MaxPages               :         24 
 UsedPages              :         23 
 AvailPages             :        105 
 MaxRegionsAlloc        :          1 
 CurrentRegionsAlloc    :          1 

[om_Opts]: 
 MinTrack               :          0
 MinCheck               :          0
 MaxTrack               :          5
 MaxCheck               :         10
 Keep                   :        100
 HowToReportErrors      :          2
 MarkAsStatic           :          0
 PagesPerRegion         :        128
 OutOfMemoryFunc        :   0x54e510
 MemoryLowFunc          :      (nil)
 ErrorHook              :   0x877110


[om_ErrorStatus]        : 'no error' (omError_NoError)
[om_InternalErrorStatus]: 'no error' (omError_NoError)

The later two lines indicate that no error was found.

PURPOSE: calling this function after a suspicious kernel function might indicate a memory corruption in it.