db9e5ec6f8
This sample demonstrates how demand paging can be leveraged to deal with firmware bigger than the available RAM if XIP is not possible. Select code can be tagged to be loaded into memory on demand, and also be automatically evicted for more code to be executed when memory is exhausted. Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
76 lines
2.1 KiB
C
76 lines
2.1 KiB
C
/*
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* Copyright (c) 2024 BayLibre SAS
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#include <zephyr/kernel.h>
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#include <zephyr/linker/sections.h>
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#include <mmu.h> /* for k_mem_num_pagefaults_get() */
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/*
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* We want to artificially create a huge body of code hence the volatile
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* to prevent the compiler from optimizing everything down.
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*/
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volatile long foo_val1;
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volatile long foo_val2;
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/*
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* This function is tagged with __ondemand_func to be placed in a special
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* "ondemand" segment by the linker. This means it is not loaded into memory
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* at boot time but rather page-by-page on demand when actually executed.
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* It is also subject to being evicted when memory reclamation occurs.
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*/
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static void __ondemand_func huge_evictable_function(void)
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{
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foo_val1 = 13131313;
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foo_val2 = 45454545;
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#define CODE \
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foo_val1 *= foo_val2; \
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foo_val2 += 1234567; \
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foo_val1 -= 9876543210; \
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__asm__ __volatile__ (".rep 1000; nop; .endr");
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#define REPEAT_10(x) x x x x x x x x x x
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#define REPEAT_1000(x) REPEAT_10(REPEAT_10(REPEAT_10(x)))
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REPEAT_1000(CODE)
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#undef REPEAT_1000
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#undef REPEAT_10
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#undef CODE
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}
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int main(void)
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{
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size_t free_pages_before, free_pages_after;
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unsigned long faults_before, faults_after;
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printk("Calling huge body of code that doesn't fit in memory\n");
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free_pages_before = k_mem_free_get() / CONFIG_MMU_PAGE_SIZE;
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faults_before = k_mem_num_pagefaults_get();
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huge_evictable_function();
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free_pages_after = k_mem_free_get() / CONFIG_MMU_PAGE_SIZE;
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faults_after = k_mem_num_pagefaults_get();
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printk("free memory pages: from %zd to %zd, %ld page faults\n",
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free_pages_before, free_pages_after, faults_after - faults_before);
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printk("Calling it a second time\n");
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free_pages_before = k_mem_free_get() / CONFIG_MMU_PAGE_SIZE;
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faults_before = k_mem_num_pagefaults_get();
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huge_evictable_function();
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free_pages_after = k_mem_free_get() / CONFIG_MMU_PAGE_SIZE;
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faults_after = k_mem_num_pagefaults_get();
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printk("free memory pages: from %zd to %zd, %ld page faults\n",
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free_pages_before, free_pages_after, faults_after - faults_before);
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printk("Done.\n");
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return 0;
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}
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