X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Fthreads%2Fpalloc.c;h=f7d49b2ea47e003a54ab54ab6d766423f89daa9c;hb=8382bdd7884a6d38f7529e0517dd9a7083f4ce73;hp=a0196ace19665fe13c4c369283e6928c9801d26f;hpb=bf866bc97d077fa3757b4aceaa7a6b41e7298c73;p=pintos-anon

diff --git a/src/threads/palloc.c b/src/threads/palloc.c
index a0196ac..f7d49b2 100644
--- a/src/threads/palloc.c
+++ b/src/threads/palloc.c
@@ -1,73 +1,183 @@
-#include "palloc.h"
+#include "threads/palloc.h"
+#include <bitmap.h>
+#include <debug.h>
+#include <round.h>
 #include <stddef.h>
 #include <stdint.h>
-#include "debug.h"
-#include "init.h"
-#include "loader.h"
-#include "lib.h"
-#include "mmu.h"
-
-/* A free page owned by the page allocator. */
-struct page
+#include <stdio.h>
+#include <string.h>
+#include "threads/init.h"
+#include "threads/loader.h"
+#include "threads/mmu.h"
+#include "threads/synch.h"
+
+/* Page allocator.  Hands out memory in page-size (or
+   page-multiple) chunks.  See malloc.h for an allocator that
+   hands out smaller chunks.
+
+   System memory is divided into two "pools" called the kernel
+   and user pools.  The user pool is for user (virtual) memory
+   pages, the kernel pool for everything else.  The idea here is
+   that the kernel needs to have memory for its own operations
+   even if user processes are swapping like mad.
+
+   By default, half of system RAM is given to the kernel pool and
+   half to the user pool.  That should be huge overkill for the
+   kernel pool, but that's just fine for demonstration purposes. */
+
+/* A memory pool. */
+struct pool
   {
-    struct page *next;  /* Next free page, or null at end of chain. */
+    struct lock lock;                   /* Mutual exclusion. */
+    struct bitmap *used_map;            /* Bitmap of free pages. */
+    uint8_t *start, *end;               /* Start and end of pool. */
   };
 
-static struct page *free_pages;
-static uint8_t *uninit_start, *uninit_end;
+/* Two pools: one for kernel data, one for user pages. */
+struct pool kernel_pool, user_pool;
+
+static void init_pool (struct pool *, void *start, void *end,
+                       const char *name);
+static bool page_from_pool (const struct pool *, void *page);
 
+/* Initializes the page allocator. */
 void
 palloc_init (void) 
 {
-  /* Kernel static code and data, in 4 kB pages.
-     
-     We can figure this out because the linker records the start
-     and end of the kernel as _start and _end.  See
-     kernel.lds. */
-  extern char _start, _end;
-  size_t kernel_pages;  
-  kernel_pages = (&_end - &_start + 4095) / 4096;
-
-  /* Then we know how much is available to allocate. */
-  uninit_start = ptov (LOADER_KERN_BASE + kernel_pages * PGSIZE);
-  uninit_end = ptov (ram_pages * PGSIZE);
+  /* End of the kernel as recorded by the linker.
+     See kernel.lds.S. */
+  extern char _end;
+
+  /* Free memory. */
+  uint8_t *free_start = pg_round_up (&_end);
+  uint8_t *free_end = ptov (ram_pages * PGSIZE);
+  size_t free_pages = (free_end - free_start) / PGSIZE;
+  uint8_t *free_middle = free_start + free_pages / 2 * PGSIZE;
+
+  /* Give half of memory to kernel, half to user. */
+  init_pool (&kernel_pool, free_start, free_middle, "kernel pool");
+  init_pool (&user_pool, free_middle, free_end, "user pool");
 }
 
+/* Obtains and returns a group of PAGE_CNT contiguous free pages.
+   If PAL_USER is set, the pages are obtained from the user pool,
+   otherwise from the kernel pool.  If PAL_ZERO is set in FLAGS,
+   then the pages are filled with zeros.  If too few pages are
+   available, returns a null pointer, unless PAL_ASSERT is set in
+   FLAGS, in which case the kernel panics. */
 void *
-palloc_get (enum palloc_flags flags)
+palloc_get_multiple (enum palloc_flags flags, size_t page_cnt)
 {
-  struct page *page;
+  struct pool *pool = flags & PAL_USER ? &user_pool : &kernel_pool;
+  void *pages;
+  size_t page_idx;
 
-  if (free_pages == NULL && uninit_start < uninit_end) 
-    {
-      palloc_free (uninit_start);
-      uninit_start += PGSIZE;
-    }
+  if (page_cnt == 0)
+    return NULL;
 
-  page = free_pages;
-  if (page != NULL) 
+  lock_acquire (&pool->lock);
+
+  page_idx = bitmap_scan_and_flip (pool->used_map, 0, page_cnt, false);
+  if (page_idx != BITMAP_ERROR)
+    pages = pool->start + PGSIZE * page_idx;
+  else
+    pages = NULL;
+
+  if (pages != NULL) 
     {
-      free_pages = page->next;
       if (flags & PAL_ZERO)
-        memset (page, 0, PGSIZE);
+        memset (pages, 0, PGSIZE * page_cnt);
     }
   else 
     {
       if (flags & PAL_ASSERT)
-        panic ("palloc_get: out of pages");
+        PANIC ("palloc_get: out of pages");
     }
+
+  lock_release (&pool->lock);
   
-  return page;
+  return pages;
 }
 
+/* Obtains and returns a single free page.
+   If PAL_USER is set, the page is obtained from the user pool,
+   otherwise from the kernel pool.  If PAL_ZERO is set in FLAGS,
+   then the page is filled with zeros.  If no pages are
+   available, returns a null pointer, unless PAL_ASSERT is set in
+   FLAGS, in which case the kernel panics. */
+void *
+palloc_get_page (enum palloc_flags flags) 
+{
+  return palloc_get_multiple (flags, 1);
+}
+
+/* Frees the PAGE_CNT pages starting at PAGES. */
 void
-palloc_free (void *page_) 
+palloc_free_multiple (void *pages, size_t page_cnt) 
 {
-  struct page *page = page_;
-  ASSERT((uintptr_t) page % PGSIZE == 0);
+  struct pool *pool;
+  size_t page_idx;
+
+  ASSERT (pg_ofs (pages) == 0);
+  if (pages == NULL || page_cnt == 0)
+    return;
+
+  if (page_from_pool (&kernel_pool, pages))
+    pool = &kernel_pool;
+  else if (page_from_pool (&user_pool, pages))
+    pool = &user_pool;
+  else
+    NOT_REACHED ();
+
+  page_idx = pg_no (pages) - pg_no (pool->start);
+  ASSERT (pg_no (pages) + page_cnt <= pg_no (pool->end));
+
 #ifndef NDEBUG
-  memset (page, 0xcc, PGSIZE);
+  memset (pages, 0xcc, PGSIZE * page_cnt);
 #endif
-  page->next = free_pages;
-  free_pages = page;
+
+  lock_acquire (&pool->lock);
+  ASSERT (bitmap_all (pool->used_map, page_idx, page_idx + page_cnt));
+  bitmap_set_multiple (pool->used_map, page_idx, page_idx + page_cnt, false);
+  lock_release (&pool->lock);
+}
+
+/* Frees the page at PAGE. */
+void
+palloc_free_page (void *page) 
+{
+  palloc_free_multiple (page, 1);
+}
+
+/* Initializes pool P as starting at START and ending at END,
+   naming it NAME for debugging purposes. */
+static void
+init_pool (struct pool *p, void *start, void *end, const char *name) 
+{
+  size_t bitmap_size;
+  size_t page_cnt;
+
+  ASSERT (pg_ofs (start) == 0);
+  ASSERT (pg_ofs (end) == 0);
+  ASSERT (end > start);
+
+  page_cnt = pg_no (end) - pg_no (start);
+  printf ("%d kB allocated for %s.\n", (PGSIZE / 1024) * page_cnt, name);
+
+  lock_init (&p->lock, name);
+  bitmap_size = ROUND_UP (bitmap_needed_bytes (page_cnt), PGSIZE);
+  p->used_map = bitmap_create_preallocated (page_cnt, start, bitmap_size);
+  p->start = start + bitmap_size;
+  p->end = end;
+  ASSERT (p->end > p->start);
+}
+
+/* Returns true if PAGE was allocated from POOL,
+   false otherwise. */
+static bool
+page_from_pool (const struct pool *pool, void *page_) 
+{
+  uint8_t *page = page_;
+
+  return page >= pool->start && page < pool->end;
 }