mm: use linked-list-allocator as kmalloc

I'll implement my own allocator later. Currently using linked-list
allocator [1] to manage the kernel heap (as in kmalloc, not vmalloc). It
manages the ID-mapped region (from VA 0xffff_8000_0000_0000). This
allocator is initialized to use the _largest_ physical memory block. If
the kernel image (text and data) live in this zone then skip the
occupied part.

Key difference between kmalloc and vmalloc:
- kmalloc pretty much manages the physical memory: the allocated address
  are within the id-mapped region (see above) therefore the allocated
  memory must also be contigous in physical memory. Such memory MUST NOT
  page fault. This is prone to fragmentation, so do not use kmalloc to
  allocate big objects (e.g. bigger than one 4k page).
- vmalloc manages kernel heap memory and the mapping is managed by
  paging. Such memory could trigger pagefault in kernel mode.

Note that the kmalloc conflicts with the previous used stack based PMA
as they operates on the same VM zone.

References: [1] https://github.com/rust-osdev/linked-list-allocator
Signed-off-by: Tianhao Wang <shrik3@mailbox.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/boot/startup-x86_64.s b/boot/startup-x86_64.s
index 2883996..bbd7172 100644
--- a/boot/startup-x86_64.s
+++ b/boot/startup-x86_64.s
@@ -274,7 +274,7 @@ pdp1:
 pt_end:
 ; reserve 8MiB for frame alloc.
 ; (see linker file)
-[SECTION .global_free_page_stack]
-free_page_stack:
-	resb   8388608
-	alignb 4096
+;[SECTION .global_free_page_stack]
+;free_page_stack:
+;	resb   8388608
+;	alignb 4096