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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Zhang Boyang <zhangboyang.id@gmail.com>
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Date: Sun, 29 Jan 2023 19:49:32 +0800
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Subject: [PATCH] mm: Preallocate some space when adding new regions
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When grub_memalign() encounters out-of-memory, it will try
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grub_mm_add_region_fn() to request more memory from system firmware.
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However, it doesn't preallocate memory space for future allocation
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requests. In extreme cases, it requires one call to
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grub_mm_add_region_fn() for each memory allocation request. This can
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be very slow.
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This patch introduces GRUB_MM_HEAP_GROW_EXTRA, the minimal heap growth
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granularity. The new region size is now set to the bigger one of its
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original value and GRUB_MM_HEAP_GROW_EXTRA. Thus, it will result in some
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memory space preallocated if current allocations request is small.
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The value of GRUB_MM_HEAP_GROW_EXTRA is set to 1MB. If this value is
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smaller, the cost of small memory allocations will be higher. If this
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value is larger, more memory will be wasted and it might cause
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out-of-memory on machines with small amount of RAM.
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Signed-off-by: Zhang Boyang <zhangboyang.id@gmail.com>
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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(cherry picked from commit 21869baec15239b6d99122b32b14a778af4c754f)
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---
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grub-core/kern/mm.c | 6 ++++++
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1 file changed, 6 insertions(+)
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diff --git a/grub-core/kern/mm.c b/grub-core/kern/mm.c
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index f29a3e5cbd..cc8a4703bc 100644
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--- a/grub-core/kern/mm.c
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+++ b/grub-core/kern/mm.c
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@@ -123,6 +123,9 @@
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/* The size passed to grub_mm_add_region_fn() is aligned up by this value. */
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#define GRUB_MM_HEAP_GROW_ALIGN 4096
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+/* Minimal heap growth granularity when existing heap space is exhausted. */
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+#define GRUB_MM_HEAP_GROW_EXTRA 0x100000
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+
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grub_mm_region_t grub_mm_base;
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grub_mm_add_region_func_t grub_mm_add_region_fn;
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@@ -471,6 +474,9 @@ grub_memalign (grub_size_t align, grub_size_t size)
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if (grub_add (size + align, GRUB_MM_MGMT_OVERHEAD, &grow))
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goto fail;
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+ /* Preallocate some extra space if heap growth is small. */
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+ grow = grub_max (grow, GRUB_MM_HEAP_GROW_EXTRA);
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+
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/* Align up heap growth to make it friendly to CPU/MMU. */
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if (grow > ~(grub_size_t) (GRUB_MM_HEAP_GROW_ALIGN - 1))
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goto fail;
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