How does Linux allocate memory for its allocator?

[jrhetf4xb]

Hi,

I was recently delving into the details of Linux's memory management as I want to implement something similar, so I was hoping if someone who's familiar with the details could help me understand one thing. Apparently the physical memory manager is a buddy algorithm, which is further specialised to return blocks of pages of a particular order (0 to 9, with 0 being just a single page). For each order the blocks are stored as a linked list. Say if a block of order 5 is requested but is not found on the list of order 5 blocks, the algorithm searches for a block in order 6, splits it into two, gives the requested half and moves the other half an order lower (as it is half in size).
What I don't get is how the kernel stores these structures, or how it allocates space for them. Since for order 0 pages you would need 1M entries (each is a 4KiB page), does it mean that the kernel allocates 1MiB * sizeof(struct page)? What about the blocks of order 1 and above? Does the kernel reuse allocated blocks by marking them as a higher order, and when it needs to split it in two just return the block and get one that is unused?

[linguofreak]

Hi,

I was recently delving into the details of Linux's memory management as I want to implement something similar, so I was hoping if someone who's familiar with the details could help me understand one thing. Apparently the physical memory manager is a buddy algorithm, which is further specialised to return blocks of pages of a particular order (0 to 9, with 0 being just a single page). For each order the blocks are stored as a linked list. Say if a block of order 5 is requested but is not found on the list of order 5 blocks, the algorithm searches for a block in order 6, splits it into two, gives the requested half and moves the other half an order lower (as it is half in size).
What I don't get is how the kernel stores these structures, or how it allocates space for them. Since for order 0 pages you would need 1M entries (each is a 4KiB page), does it mean that the kernel allocates 1MiB * sizeof(struct page)? What about the blocks of order 1 and above? Does the kernel reuse allocated blocks by marking them as a higher order, and when it needs to split it in two just return the block and get one that is unused?

I'm not intimately familiar with how Linux does things, but the physical allocator only needs to store information on the blocks that are free. Since the blocks its dealing with aren't being used for anything else, it can store the information regarding each block within the block itself, so that is almost certainly what Linux does.