GNU malloc_info(): get really allocated memory?

Question

I'm trying to investigate memory use of a large multi-threaded server. According to mallinfo(), I get arena=350M and fordblks=290M, which suggests most of the space is actually wasted inside malloc(). The malloc_info() function gives a nice XML data structure that is supposed to be self-explanatory. Still, can someone explain to me

• Is heap 0 special? Is the that main arena in which all others reside?
• Are the <size from=.../> chunk allocated, free/available or both?
• What is the <system> element? Memory allocated using mmap()/sbrk()?
• What is the <aspace> element? Available memory?
• What about <aspace type="mprotect" .../>?

Just for a start, I'd like to be able to plot total memory allocated by the application, i.e., everything allocated and not yet freed, according to what malloc() thinks.

Answer 1

A large amount of virtual memory usage is not necessarily a problem. The default malloc implementation will allocate large amounts of storage per thread in order to avoid contention issues. This happens particularly on 64-bit implementations which are pretty common nowadays. You should not worry unless you experience problems with the size of resident memory or you get paging problems.

Kevin Grigorenko has written a number of blog posts which deal with memory usage in relation to WebSphere, but they are applicable to any large multi-threaded process.