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\chapter{Bacula Memory Management}
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\index{Management!Bacula Memory}
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\index{Bacula Memory Management}
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\addcontentsline{toc}{section}{Bacula Memory Management}
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\addcontentsline{toc}{subsection}{General}
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This document describes the memory management routines that are used in Bacula
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and is meant to be a technical discussion for developers rather than part of
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Since Bacula may be called upon to handle filenames of varying and more or
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less arbitrary length, special attention needs to be used in the code to
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ensure that memory buffers are sufficiently large. There are four
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possibilities for memory usage within {\bf Bacula}. Each will be described in
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\item Statically allocated memory.
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\item Dynamically allocated memory using malloc() and free().
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\item Non-pooled memory.
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\subsection{Statically Allocated Memory}
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\index{Statically Allocated Memory}
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\index{Memory!Statically Allocated}
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\addcontentsline{toc}{subsubsection}{Statically Allocated Memory}
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Statically allocated memory is of the form:
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char buffer[MAXSTRING];
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The use of this kind of memory is discouraged except when you are 100\% sure
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that the strings to be used will be of a fixed length. One example of where
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this is appropriate is for {\bf Bacula} resource names, which are currently
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limited to 127 characters (MAX\_NAME\_LENGTH). Although this maximum size may
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change, particularly to accommodate Unicode, it will remain a relatively small
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\subsection{Dynamically Allocated Memory}
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\index{Dynamically Allocated Memory}
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\index{Memory!Dynamically Allocated}
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\addcontentsline{toc}{subsubsection}{Dynamically Allocated Memory}
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Dynamically allocated memory is obtained using the standard malloc() routines.
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This kind of memory can be released with:
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It is recommended to use this kind of memory only when you are sure that you
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know the memory size needed and the memory will be used for short periods of
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time -- that is it would not be appropriate to use statically allocated
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memory. An example might be to obtain a large memory buffer for reading and
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writing files. When {\bf SmartAlloc} is enabled, the memory obtained by
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malloc() will automatically be checked for buffer overwrite (overflow) during
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the free() call, and all malloc'ed memory that is not released prior to
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termination of the program will be reported as Orphaned memory.
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\subsection{Pooled and Non-pooled Memory}
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\index{Memory!Pooled and Non-pooled}
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\index{Pooled and Non-pooled Memory}
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\addcontentsline{toc}{subsubsection}{Pooled and Non-pooled Memory}
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In order to facility the handling of arbitrary length filenames and to
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efficiently handle a high volume of dynamic memory usage, we have implemented
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routines between the C code and the malloc routines. The first is called
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``Pooled'' memory, and is memory, which once allocated and then released, is
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not returned to the system memory pool, but rather retained in a Bacula memory
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pool. The next request to acquire pooled memory will return any free memory
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block. In addition, each memory block has its current size associated with the
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block allowing for easy checking if the buffer is of sufficient size. This
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kind of memory would normally be used in high volume situations (lots of
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malloc()s and free()s) where the buffer length may have to frequently change
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to adapt to varying filename lengths.
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The non-pooled memory is handled by routines similar to those used for pooled
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memory, allowing for easy size checking. However, non-pooled memory is
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returned to the system rather than being saved in the Bacula pool. This kind
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of memory would normally be used in low volume situations (few malloc()s and
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free()s), but where the size of the buffer might have to be adjusted
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\paragraph*{Types of Memory Pool:}
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Currently there are three memory pool types:
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\item PM\_NOPOOL -- non-pooled memory.
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\item PM\_FNAME -- a filename pool.
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\item PM\_MESSAGE -- a message buffer pool.
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\item PM\_EMSG -- error message buffer pool.
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\paragraph*{Getting Memory:}
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To get memory, one uses:
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void *get_pool_memory(pool);
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where {\bf pool} is one of the above mentioned pool names. The size of the
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memory returned will be determined by the system to be most appropriate for
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If you wish non-pooled memory, you may alternatively call:
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void *get_memory(size_t size);
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The buffer length will be set to the size specified, and it will be assigned
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to the PM\_NOPOOL pool (no pooling).
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\paragraph*{Releasing Memory:}
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To free memory acquired by either of the above two calls, use:
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void free_pool_memory(void *buffer);
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where buffer is the memory buffer returned when the memory was acquired. If
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the memory was originally allocated as type PM\_NOPOOL, it will be released to
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the system, otherwise, it will be placed on the appropriate Bacula memory pool
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free chain to be used in a subsequent call for memory from that pool.
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\paragraph*{Determining the Memory Size:}
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To determine the memory buffer size, use:
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size_t sizeof_pool_memory(void *buffer);
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\paragraph*{Resizing Pool Memory:}
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To resize pool memory, use:
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void *realloc_pool_memory(void *buffer);
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The buffer will be reallocated, and the contents of the original buffer will
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be preserved, but the address of the buffer may change.
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\paragraph*{Automatic Size Adjustment:}
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To have the system check and if necessary adjust the size of your pooled
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void *check_pool_memory_size(void *buffer, size_t new-size);
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where {\bf new-size} is the buffer length needed. Note, if the buffer is
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already equal to or larger than {\bf new-size} no buffer size change will
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occur. However, if a buffer size change is needed, the original contents of
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the buffer will be preserved, but the buffer address may change. Many of the
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low level Bacula subroutines expect to be passed a pool memory buffer and use
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this call to ensure the buffer they use is sufficiently large.
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\paragraph*{Releasing All Pooled Memory:}
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In order to avoid orphaned buffer error messages when terminating the program,
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void close_memory_pool();
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to free all unused memory retained in the Bacula memory pool. Note, any memory
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not returned to the pool via free\_pool\_memory() will not be released by this
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\paragraph*{Pooled Memory Statistics:}
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For debugging purposes and performance tuning, the following call will print
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the current memory pool statistics:
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void print_memory_pool_stats();
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an example output is:
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Pool Maxsize Maxused Inuse
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manuals/en/developers/mempool.tex
