Making a simple Dynamic Memory Allocator (malloc)

In this video I discuss how to make a simple dynamic Memory Allocator.

CODECRAFTERS x DWB:

[braulio]

Creo que no he encontrado a nadie que lo explique mejor . Gracias!!!

[ENDESGA]

I love your content so much. Cannot wait to watch this

[nicholas_obert]

3:30 the real problem with defragmentation is that you cannot move heap data around, as you would invalidate any pointer that was acquired before the defragmentation. As far as I know, generic heap defragmentation is impossible in low level languages, except maybe for a very restricted set of programs.
I can only think of heap defragmentation being possible in high-level languages where the programmer cannot ever directly access pointers and heap data is always kept behind two levels of indirection (an object on the heap is owned by a reference counting smart pointer and the programmer is given a reference to the smart pointer), allowing for the mutation of the pointer to the actual heap data (for defrag) without invalidating any reference the programmer may have lying around.

[groxxxx]

0:31 only few know what the number 0x7c00 really means

[isidroarias]

free() needs to know the size passed to malloc(). It can not turn off all the contiguous '1's because it could deallocate another blocks

[iagojacob]

I loved your videos! where can I learn more about making an OS?

[Skybrg]

Is a bitmap commonly used? I thought the most common is a freelist since that makes scanning easy and is an implicit data structure (so it works well with things like sbrk).

[panjak]

Ummmm.... But when you defrag the blocks, how do you notify the consument its pointer to the data has changed ?
What I mean by that:

int *data = malloc(N); // data now points to 0x123
// allocate bunch of data and free everything except data*, so that memory is fragmented
// at some point defrag in malloc runs once you allocated something
// data* still points to 0x123, however by defragging everything has moved to lets say beginning, so the actual data is stored at 0x0
data[0] = 5; // CG, you've just pagefaulted.

[Bard_Gaming]

Can you maybe show how one would implement a dynamic memory allocator that also keeps track of the amount of memory allocated, such that calling free() doesn't require the additional size parameter?

[yarrakobama]

void* my_alloc(size_t bytes) { return malloc(bytes); } // ez

[FamilyAcc-yquj]

We need your help for making an amd64 OS because I understand the best from you.

[Pranavbg_]

When will we start making the GUI of this OS 😢

[josetheyose]

Could you help me with the os tutorial? I created an array inside the c file, and when I try to access the array, all the values are null or 0. Could you show me how to fix this?

[darknais]

It's not true you can move memory in linear way with memove moving a pointer elsewhere

[pixfri]

To access heap memory in C++ you don’t use malloc/free nor new and delete, they are considered a bad practice since C++11 since you need to manually manage objects lifetimes and when they are deleted, instead you need to use smart pointers

Edit: I know this video talks about a lower level approach, I was just speaking about a more general use case.

[ゾカリクゾ]

ill try out the free project for september in codecrafters, if it's cool enough