[PATCH v2 1/1] mm: Better handling of adding new regions

[Zhang Boyang]

The code of dynamically adding new regions has two problems. First, it
always invalidate disk caches, which decreases performance severely.
Second, it request exactly "size" bytes for new region, ignoring region
management overheads.

This patch makes adding new regions more priority than disk cache
invalidating. This patch also use "size + align + GRUB_MM_HEAP_GROW" as
the size of new region. GRUB_MM_HEAP_GROW is set to 1MiB. This value can
address the region overheads, and it can also improve the performance of
small allocations when default heap is full.

Fixes: 887f98f0db43 (mm: Allow dynamically requesting additional memory regions)

Signed-off-by: Zhang Boyang <zhangboyang.id@gmail.com>
---
 grub-core/kern/mm.c | 27 +++++++++++++++------------
 include/grub/mm.h   |  2 ++
 2 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/grub-core/kern/mm.c b/grub-core/kern/mm.c
index 75f6eacbe..0836b9538 100644
--- a/grub-core/kern/mm.c
+++ b/grub-core/kern/mm.c
@@ -410,18 +410,21 @@ grub_memalign (grub_size_t align, grub_size_t size)
 {
   grub_mm_region_t r;
   grub_size_t n = ((size + GRUB_MM_ALIGN - 1) >> GRUB_MM_ALIGN_LOG2) + 1;
+  grub_size_t grow;
   int count = 0;
 
   if (!grub_mm_base)
     goto fail;
 
-  if (size > ~(grub_size_t) align)
+  if (size > ~(grub_size_t) align ||
+      (size + align) > ~(grub_size_t) GRUB_MM_HEAP_GROW)
     goto fail;
 
   /* We currently assume at least a 32-bit grub_size_t,
-     so limiting allocations to <adress space size> - 1MiB
+     so limiting heap growth to <adress space size> - 1MiB
      in name of sanity is beneficial. */
-  if ((size + align) > ~(grub_size_t) 0x100000)
+  grow = size + align + GRUB_MM_HEAP_GROW;
+  if (grow > ~(grub_size_t) 0x100000)
     goto fail;
 
   align = (align >> GRUB_MM_ALIGN_LOG2);
@@ -443,22 +446,16 @@ grub_memalign (grub_size_t align, grub_size_t size)
   switch (count)
     {
     case 0:
-      /* Invalidate disk caches.  */
-      grub_disk_cache_invalidate_all ();
-      count++;
-      goto again;
-
-    case 1:
       /* Request additional pages, contiguous */
       count++;
 
       if (grub_mm_add_region_fn != NULL &&
-          grub_mm_add_region_fn (size, GRUB_MM_ADD_REGION_CONSECUTIVE) == 
GRUB_ERR_NONE)
+          grub_mm_add_region_fn (grow, GRUB_MM_ADD_REGION_CONSECUTIVE) == 
GRUB_ERR_NONE)
        goto again;
 
       /* fallthrough  */
 
-    case 2:
+    case 1:
       /* Request additional pages, anything at all */
       count++;
 
@@ -468,12 +465,18 @@ grub_memalign (grub_size_t align, grub_size_t size)
            * Try again even if this fails, in case it was able to partially
            * satisfy the request
            */
-          grub_mm_add_region_fn (size, GRUB_MM_ADD_REGION_NONE);
+          grub_mm_add_region_fn (grow, GRUB_MM_ADD_REGION_NONE);
           goto again;
         }
 
       /* fallthrough */
 
+    case 2:
+      /* Invalidate disk caches.  */
+      grub_disk_cache_invalidate_all ();
+      count++;
+      goto again;
+
     default:
       break;
     }
diff --git a/include/grub/mm.h b/include/grub/mm.h
index f3bf87fa0..463096cd8 100644
--- a/include/grub/mm.h
+++ b/include/grub/mm.h
@@ -29,6 +29,8 @@
 # define NULL  ((void *) 0)
 #endif
 
+#define GRUB_MM_HEAP_GROW 0x100000
+
 #define GRUB_MM_ADD_REGION_NONE        0
 #define GRUB_MM_ADD_REGION_CONSECUTIVE (1 << 0)
 
-- 
2.30.2