[PATCH 05/19] mm: when adding a region, merge with region after as well as before

[Daniel Axtens]

On x86_64-efi (at least) regions seem to be added from top down. The mm
code will merge a new region with an existing region that comes
immediately before the new region. This allows larger allocations to be
satisfied that would otherwise be the case.

On powerpc-ieee1275, however, regions are added from bottom up. So if
we add 3x 32MB regions, we can still only satisfy a 32MB allocation,
rather than the 96MB allocation we might otherwise be able to satisfy.

 * Define 'post_size' as being bytes lost to the end of an allocation
   due to being given weird sizes from firmware that are not multiples
   of GRUB_MM_ALIGN.

 * Allow merging of regions immediately _after_ existing regions, not
   just before. As with the other approach, we create an allocated
   block to represent the new space and the pass it to grub_free() to
   get the metadata right.

Signed-off-by: Daniel Axtens <dja@axtens.net>
---
 grub-core/kern/mm.c       | 55 +++++++++++++++++++++++++--------------
 include/grub/mm_private.h | 15 +++++++++++
 2 files changed, 51 insertions(+), 19 deletions(-)

diff --git a/grub-core/kern/mm.c b/grub-core/kern/mm.c
index c070afc621f8..835ed8a8f6f9 100644
--- a/grub-core/kern/mm.c
+++ b/grub-core/kern/mm.c
@@ -129,25 +129,41 @@ grub_mm_init_region (void *addr, grub_size_t size)
     size = ((grub_addr_t) -0x1000) - (grub_addr_t) addr;
 
   for (p = &grub_mm_base, q = *p; q; p = &(q->next), q = *p)
-    if ((grub_uint8_t *) addr + size + q->pre_size == (grub_uint8_t *) q)
-      {
-       r = (grub_mm_region_t) ALIGN_UP ((grub_addr_t) addr, GRUB_MM_ALIGN);
-       *r = *q;
-       r->pre_size += size;
-       
-       if (r->pre_size >> GRUB_MM_ALIGN_LOG2)
-         {
-           h = (grub_mm_header_t) (r + 1);
-           h->size = (r->pre_size >> GRUB_MM_ALIGN_LOG2);
-           h->magic = GRUB_MM_ALLOC_MAGIC;
-           r->size += h->size << GRUB_MM_ALIGN_LOG2;
-           r->pre_size &= (GRUB_MM_ALIGN - 1);
-           *p = r;
-           grub_free (h + 1);
-         }
-       *p = r;
-       return;
-      }
+    {
+      /* Does this region come _before_ an existing region? */
+      if ((grub_uint8_t *) addr + size + q->pre_size == (grub_uint8_t *) q)
+       {
+         r = (grub_mm_region_t) ALIGN_UP ((grub_addr_t) addr, GRUB_MM_ALIGN);
+         *r = *q;
+         r->pre_size += size;
+
+         if (r->pre_size >> GRUB_MM_ALIGN_LOG2)
+           {
+             h = (grub_mm_header_t) (r + 1);
+             h->size = (r->pre_size >> GRUB_MM_ALIGN_LOG2);
+             h->magic = GRUB_MM_ALLOC_MAGIC;
+             r->size += h->size << GRUB_MM_ALIGN_LOG2;
+             r->pre_size &= (GRUB_MM_ALIGN - 1);
+             *p = r;
+             grub_free (h + 1);
+           }
+         *p = r;
+         return;
+       }
+
+      /* Does this region come _after_ an existing region? */
+      if ((grub_uint8_t *)q + sizeof(*q) + q->size + q->post_size ==
+         (grub_uint8_t *) addr)
+       {
+         h = (grub_mm_header_t) ((grub_uint8_t *)addr - q->post_size);
+         h->size = (size + q->post_size) >> GRUB_MM_ALIGN_LOG2;
+         h->magic = GRUB_MM_ALLOC_MAGIC;
+         q->size += h->size << GRUB_MM_ALIGN_LOG2;
+         q->post_size = (q->post_size + size) & (GRUB_MM_ALIGN - 1);
+         grub_free (h + 1);
+         return;
+       }
+    }
 
   /* Allocate a region from the head.  */
   r = (grub_mm_region_t) ALIGN_UP ((grub_addr_t) addr, GRUB_MM_ALIGN);
@@ -166,6 +182,7 @@ grub_mm_init_region (void *addr, grub_size_t size)
   r->first = h;
   r->pre_size = (grub_addr_t) r - (grub_addr_t) addr;
   r->size = (h->size << GRUB_MM_ALIGN_LOG2);
+  r->post_size = size - r->size;
 
   /* Find where to insert this region. Put a smaller one before bigger ones,
      to prevent fragmentation.  */
diff --git a/include/grub/mm_private.h b/include/grub/mm_private.h
index 533b47173e18..0effbc45a668 100644
--- a/include/grub/mm_private.h
+++ b/include/grub/mm_private.h
@@ -74,8 +74,23 @@ typedef struct grub_mm_region
    */
   grub_size_t pre_size;
 
+  /* Likewise, the post-size is the number of bytes we wasted at the end
+     of the allocation because it wasn't a multiple of GRUB_MM_ALIGN
+   */
+  grub_size_t post_size;
+
   /* How many bytes are in this region? (free and allocated) */
   grub_size_t size;
+
+  /* pad to a multiple of cell size */
+#if GRUB_CPU_SIZEOF_VOID_P == 4
+  char padding[4+4+4];
+#elif GRUB_CPU_SIZEOF_VOID_P == 8
+  char padding[8+8+8];
+#else
+# error "unknown word size"
+#endif
+
 }
 *grub_mm_region_t;
 
-- 
2.30.2