From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001

From: Zhang Boyang <zhangboyang.id@gmail.com>

Date: Sun, 29 Jan 2023 19:49:32 +0800

Subject: [PATCH] mm: Preallocate some space when adding new regions

When grub_memalign() encounters out-of-memory, it will try

grub_mm_add_region_fn() to request more memory from system firmware.

However, it doesn't preallocate memory space for future allocation

requests. In extreme cases, it requires one call to

grub_mm_add_region_fn() for each memory allocation request. This can

be very slow.

This patch introduces GRUB_MM_HEAP_GROW_EXTRA, the minimal heap growth

granularity. The new region size is now set to the bigger one of its

original value and GRUB_MM_HEAP_GROW_EXTRA. Thus, it will result in some

memory space preallocated if current allocations request is small.

The value of GRUB_MM_HEAP_GROW_EXTRA is set to 1MB. If this value is

smaller, the cost of small memory allocations will be higher. If this

value is larger, more memory will be wasted and it might cause

out-of-memory on machines with small amount of RAM.

Signed-off-by: Zhang Boyang <zhangboyang.id@gmail.com>

Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

(cherry picked from commit 21869baec15239b6d99122b32b14a778af4c754f)

---

 grub-core/kern/mm.c | 6 ++++++

 1 file changed, 6 insertions(+)

diff --git a/grub-core/kern/mm.c b/grub-core/kern/mm.c

index f29a3e5cbd..cc8a4703bc 100644

--- a/grub-core/kern/mm.c

+++ b/grub-core/kern/mm.c

@@ -123,6 +123,9 @@

 /* The size passed to grub_mm_add_region_fn() is aligned up by this value. */

 #define GRUB_MM_HEAP_GROW_ALIGN	4096

+/* Minimal heap growth granularity when existing heap space is exhausted. */

+#define GRUB_MM_HEAP_GROW_EXTRA	0x100000

+

 grub_mm_region_t grub_mm_base;

 grub_mm_add_region_func_t grub_mm_add_region_fn;

@@ -471,6 +474,9 @@ grub_memalign (grub_size_t align, grub_size_t size)

   if (grub_add (size + align, GRUB_MM_MGMT_OVERHEAD, &grow))

     goto fail;

+  /* Preallocate some extra space if heap growth is small. */

+  grow = grub_max (grow, GRUB_MM_HEAP_GROW_EXTRA);

+

   /* Align up heap growth to make it friendly to CPU/MMU. */

   if (grow > ~(grub_size_t) (GRUB_MM_HEAP_GROW_ALIGN - 1))

     goto fail;