d0f7acf9eb
An x86-64 operating system built from xv6, now largely rewritten: SMP, a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF rasteriser, and a Linux-numbered syscall ABI. No history before this point -- the tree was never under version control. This commit exists so the rename that follows has something to undo to.
124 lines
2.6 KiB
C
124 lines
2.6 KiB
C
// Physical memory allocator, intended to allocate
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// memory for user processes, kernel stacks, page table pages,
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// and pipe buffers. Allocates 4096-byte pages.
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#include "types.h"
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#include "defs.h"
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#include "param.h"
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#include "memlayout.h"
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#include "mmu.h"
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#include "spinlock.h"
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void freerange(void *vstart, void *vend);
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extern char end[]; // first address after kernel loaded from ELF file
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struct run {
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struct run *next;
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};
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struct {
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struct spinlock lock;
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int use_lock;
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struct run *freelist;
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} kmem;
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// Catch kmem.freelist corruption at the point it's touched, rather than
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// letting a bad pointer be silently returned by kalloc() and crash whatever
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// code dereferences it minutes later on an unrelated call stack.
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static void
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check_run(struct run *r, char *where)
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{
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if(r == 0)
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return;
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if((addr_t)r % PGSIZE || (char*)r < end || V2P(r) >= PHYSTOP){
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cprintf("kalloc: corrupt freelist entry %p at %s\n", r, where);
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panic("kalloc: corrupt freelist");
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}
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}
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void
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kinit1(void *vstart, void *vend)
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{
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initlock(&kmem.lock, "kmem");
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kmem.use_lock = 0;
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kmem.freelist = 0; // empty
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freerange(vstart, vend);
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}
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void
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kinit2()
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{
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kmem.use_lock = 1;
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}
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void
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freerange(void *vstart, void *vend)
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{
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char *p;
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p = (char*)PGROUNDUP((addr_t)vstart);
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for(; p + PGSIZE <= (char*)vend; p += PGSIZE)
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kfree(p);
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}
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// Free the page of physical memory pointed at by v,
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// which normally should have been returned by a
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// call to kalloc(). (The exception is when
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// initializing the allocator; see kinit above.)
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void
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kfree(char *v)
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{
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struct run *r;
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if((addr_t)v % PGSIZE || v < end || V2P(v) >= PHYSTOP)
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panic("kfree");
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// Fill with junk to catch dangling refs.
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memset(v, 1, PGSIZE);
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if(kmem.use_lock)
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acquire(&kmem.lock);
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check_run(kmem.freelist, "kfree entry");
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r = (struct run*)v;
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r->next = kmem.freelist;
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kmem.freelist = r;
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if(kmem.use_lock)
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release(&kmem.lock);
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}
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// Allocate one 4096-byte page of physical memory.
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// Returns a pointer that the kernel can use.
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// Returns 0 if the memory cannot be allocated.
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char*
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kalloc(void)
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{
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struct run *r;
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if(kmem.use_lock)
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acquire(&kmem.lock);
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check_run(kmem.freelist, "kalloc entry");
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r = kmem.freelist;
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if(r)
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kmem.freelist = r->next;
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if(kmem.use_lock)
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release(&kmem.lock);
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return (char*)r;
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}
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// Total free physical memory, in bytes. Walks the free list; only /proc
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// readers call it, so the O(n) scan is not on any hot path.
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uint64
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kalloc_free_bytes(void)
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{
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struct run *r;
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uint64 n = 0;
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if(kmem.use_lock)
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acquire(&kmem.lock);
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for(r = kmem.freelist; r; r = r->next)
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n += PGSIZE;
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if(kmem.use_lock)
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release(&kmem.lock);
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return n;
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}
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