What Every Programmer Should Know About Memory (PDF)

I just came across this PDF on reddit.com titled "What every programmer should know about memory". Its written by Ulrich Drepper from RedHat, you should know who he is.

Link to PDF

It's going to take me awhile to get through this (its 114 pages long) - but so far its a decent read. I'm currently cheating and searching through it for things that interest me. I'm currently taking in section 7.3 'Measuring Memory Usage'. This section is particularly interesting to me because I've been toying with a project of mine lately that collects massive amounts of data. Searching and sorting that data efficiently has not been easy.

Ulrich states in the PDF that using libc's malloc to store a linked list you populate for later retrieval and use is probably a bad idea. This is true, because theres no guarantee malloc will return memory that is close or even near to the next member in the linked list. There are alternatives to using the traditional libc malloc library such as obstack and Google's TCMalloc. I have toyed with TCMalloc on several occasions. Despite all of my heap mappings being in sequential order it only seems to slow down my data hungry application.

Obstack on the other hand is generally fast because it starts out mapping a larger chunk of memory, within that chunk you allocate smaller chunks to hold your data (in my case my linked list structures) which end up being in sequential order. Which is of course a lot faster to access then a list that is fragmented up.

There's lots of other good stuff in his paper, take a look for yourself.