From 83d2db91f75460e1275d67847adec0fca5a9800b Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@nephron.lcs.mit.edu>
Date: Tue, 10 Aug 2010 17:08:41 -0400
Subject: allow sbrk(-x) to de-allocate user memory
---
vm.c | 26 +++++++++++++++++++++++++-
1 file changed, 25 insertions(+), 1 deletion(-)
(limited to 'vm.c')
diff --git a/vm.c b/vm.c
index 6914dd3..8755b82 100644
--- a/vm.c
+++ b/vm.c
@@ -198,7 +198,7 @@ uva2ka(pde_t *pgdir, char *uva)
int
allocuvm(pde_t *pgdir, char *addr, uint sz)
{
- if (addr + sz >= (char*)USERTOP)
+ if (addr + sz > (char*)USERTOP)
return 0;
char *first = PGROUNDDOWN(addr);
char *last = PGROUNDDOWN(addr + sz - 1);
@@ -218,6 +218,30 @@ allocuvm(pde_t *pgdir, char *addr, uint sz)
return 1;
}
+// deallocate some of the user pages, in response to sbrk()
+// with a negative argument. if addr is not page-aligned,
+// then only deallocates starting at the next page boundary.
+int
+deallocuvm(pde_t *pgdir, char *addr, uint sz)
+{
+ if (addr + sz > (char*)USERTOP)
+ return 0;
+ char *first = (char*) PGROUNDUP((uint)addr);
+ char *last = PGROUNDDOWN(addr + sz - 1);
+ char *a;
+ for(a = first; a <= last; a += PGSIZE){
+ pte_t *pte = walkpgdir(pgdir, a, 0);
+ if(pte && (*pte & PTE_P) != 0){
+ uint pa = PTE_ADDR(*pte);
+ if(pa == 0)
+ panic("deallocuvm");
+ kfree((void *) pa, PGSIZE);
+ *pte = 0;
+ }
+ }
+ return 1;
+}
+
// free a page table and all the physical memory pages
// in the user part.
void
--
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