Should free() return memory to the OS?

[twilit sparrow]

When implementing free() should I make it munmap() free bytes to the os? Should I munmap() when a whole page is free or just chunks of memory (which wouldn’t that break the program)? Or should I just allow the user to hoard massive amounts of memory not in use? Ty!!!

[stone sinew]

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[opaque lily]

yeah you can munmap when the region you allocated using mmap isn't in use anymore

[twilit sparrow]

If I munmap a chunk of size 32 (chunk is marked as free) and then I want to allocate more mem of size 32, how will that memory be usable if it’s munmapedz Wouldn’t it be an access violation or something?

[tranquil cosmos]

you can only mmap and munmap full pages

[twilit sparrow]

Ooh okay

[tranquil cosmos]

and munmap will unmap the entire region originally allocated by mmap

[tall sinew]

You should generally not munmap to the OS

If you have a normal allocation setup this will be either semi-expensive to compute or end up fragmenting your arenas

[twilit sparrow]

About the fragments, does free() bother coalescing freed chunks that are separated by unfreed chunks? Like <free(32), unfree(32), free(32), unfree(32)> -> <free(64), unfree(32), unfree(32)> ? It seems exhaustive unless it somehow doesn’t move the unfreed memory over

[heavy carbon]

You can't just move the chunks, all the pointers would get broken

I'm not sure what you're implying

[twilit sparrow]

Yea nvm then I figured. I would be like when you realloc and it memcpys it over

Ty

!solved