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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 19:49:33 +0800
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Subject: [PATCH] mm: Avoid complex heap growth math in hot path
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We do a lot of math about heap growth in hot path of grub_memalign().
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However, the result is only used if out of memory is encountered, which
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is seldom.
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This patch moves these calculations away from hot path. These
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calculations are now only done if out of memory is encountered. This
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change can also help compiler to optimize integer overflow checks away.
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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 65bc45963014773e2062ccc63ff34a089d2e352e)
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---
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grub-core/kern/mm.c | 34 ++++++++++++++++++++--------------
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1 file changed, 20 insertions(+), 14 deletions(-)
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diff --git a/grub-core/kern/mm.c b/grub-core/kern/mm.c
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index cc8a4703bc..630d7be0e2 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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@@ -467,20 +467,7 @@ grub_memalign (grub_size_t align, grub_size_t size)
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if (size > ~(grub_size_t) align)
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goto fail;
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- /*
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- * Pre-calculate the necessary size of heap growth (if applicable),
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- * with region management overhead taken into account.
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- */
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- if (grub_add (size + align, GRUB_MM_MGMT_OVERHEAD, &grow))
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- goto fail;
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-
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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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- grow = ALIGN_UP (grow, GRUB_MM_HEAP_GROW_ALIGN);
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+ grow = size + align;
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/* We currently assume at least a 32-bit grub_size_t,
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so limiting allocations to <adress space size> - 1MiB
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@@ -510,6 +497,25 @@ grub_memalign (grub_size_t align, grub_size_t size)
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/* Request additional pages, contiguous */
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count++;
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+ /*
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+ * Calculate the necessary size of heap growth (if applicable),
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+ * with region management overhead taken into account.
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+ */
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+ if (grub_add (grow, GRUB_MM_MGMT_OVERHEAD, &grow))
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+ goto fail;
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+
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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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+ grow = ALIGN_UP (grow, GRUB_MM_HEAP_GROW_ALIGN);
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+
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+ /* Do the same sanity check again. */
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+ if (grow > ~(grub_size_t) 0x100000)
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+ goto fail;
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+
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if (grub_mm_add_region_fn != NULL &&
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grub_mm_add_region_fn (grow, GRUB_MM_ADD_REGION_CONSECUTIVE) == GRUB_ERR_NONE)
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goto again;
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