Как получить MemAvailable через язык Си

#include <stdio.h>
#include <errno.h>

#include <sys/types.h>
#include <sys/sysctl.h>
#include <sys/vmmeter.h>

int main(){
    int rc;
    u_int page_size;
    struct vmtotal vmt;
    size_t vmt_size, uint_size; 

    vmt_size = sizeof(vmt);
    uint_size = sizeof(page_size);

    rc = sysctlbyname("vm.vmtotal", &vmt, &vmt_size, NULL, 0);
    if (rc < 0){
       perror("sysctlbyname");
       return 1;
    }

    rc = sysctlbyname("vm.stats.vm.v_page_size", &page_size, &uint_size, NULL, 0);
    if (rc < 0){
       perror("sysctlbyname");
       return 1;
    }

    printf("Free memory       : %ld\n", vmt.t_free * (u_int64_t)page_size);
    printf("Available memory  : %ld\n", vmt.t_avm * (u_int64_t)page_size);

    return 0;
}

/**
 * do_sysinfo - fill in sysinfo struct
 * @info: pointer to buffer to fill
 */
static int do_sysinfo(struct sysinfo *info)
{
	unsigned long mem_total, sav_total;
	unsigned int mem_unit, bitcount;
	struct timespec64 tp;

	memset(info, 0, sizeof(struct sysinfo));

	ktime_get_boottime_ts64(&tp);
	timens_add_boottime(&tp);
	info->uptime = tp.tv_sec + (tp.tv_nsec ? 1 : 0);

	get_avenrun(info->loads, 0, SI_LOAD_SHIFT - FSHIFT);

	info->procs = nr_threads;

	si_meminfo(info);
	si_swapinfo(info);

	/*
	 * If the sum of all the available memory (i.e. ram + swap)
	 * is less than can be stored in a 32 bit unsigned long then
	 * we can be binary compatible with 2.2.x kernels.  If not,
	 * well, in that case 2.2.x was broken anyways...
	 *
	 *  -Erik Andersen <andersee@debian.org>
	 */

	mem_total = info->totalram + info->totalswap;
	if (mem_total < info->totalram || mem_total < info->totalswap)
		goto out;
	bitcount = 0;
	mem_unit = info->mem_unit;
	while (mem_unit > 1) {
		bitcount++;
		mem_unit >>= 1;
		sav_total = mem_total;
		mem_total <<= 1;
		if (mem_total < sav_total)
			goto out;
	}

	/*
	 * If mem_total did not overflow, multiply all memory values by
	 * info->mem_unit and set it to 1.  This leaves things compatible
	 * with 2.2.x, and also retains compatibility with earlier 2.4.x
	 * kernels...
	 */

	info->mem_unit = 1;
	info->totalram <<= bitcount;
	info->freeram <<= bitcount;
	info->sharedram <<= bitcount;
	info->bufferram <<= bitcount;
	info->totalswap <<= bitcount;
	info->freeswap <<= bitcount;
	info->totalhigh <<= bitcount;
	info->freehigh <<= bitcount;

out:
	return 0;
}

static void show_val_kb(struct seq_file *m, const char *s, unsigned long num)
{
	seq_put_decimal_ull_width(m, s, num << (PAGE_SHIFT - 10), 8);
	seq_write(m, " kB\n", 4);
}

static int meminfo_proc_show(struct seq_file *m, void *v)
{
	struct sysinfo i;
	unsigned long committed;
	long cached;
	long available;
	unsigned long pages[NR_LRU_LISTS];
	unsigned long sreclaimable, sunreclaim;
	int lru;

	si_meminfo(&i);
	si_swapinfo(&i);
	committed = vm_memory_committed();

	cached = global_node_page_state(NR_FILE_PAGES) -
			total_swapcache_pages() - i.bufferram;
	if (cached < 0)
		cached = 0;

	for (lru = LRU_BASE; lru < NR_LRU_LISTS; lru++)
		pages[lru] = global_node_page_state(NR_LRU_BASE + lru);

	available = si_mem_available();
	sreclaimable = global_node_page_state_pages(NR_SLAB_RECLAIMABLE_B);
	sunreclaim = global_node_page_state_pages(NR_SLAB_UNRECLAIMABLE_B);

	show_val_kb(m, "MemTotal:       ", i.totalram);
	show_val_kb(m, "MemFree:        ", i.freeram);
	show_val_kb(m, "MemAvailable:   ", available);
	show_val_kb(m, "Buffers:        ", i.bufferram);
	show_val_kb(m, "Cached:         ", cached);
	show_val_kb(m, "SwapCached:     ", total_swapcache_pages());
	show_val_kb(m, "Active:         ", pages[LRU_ACTIVE_ANON] +
					   pages[LRU_ACTIVE_FILE]);
	show_val_kb(m, "Inactive:       ", pages[LRU_INACTIVE_ANON] +
					   pages[LRU_INACTIVE_FILE]);
	show_val_kb(m, "Active(anon):   ", pages[LRU_ACTIVE_ANON]);
	show_val_kb(m, "Inactive(anon): ", pages[LRU_INACTIVE_ANON]);
	show_val_kb(m, "Active(file):   ", pages[LRU_ACTIVE_FILE]);
	show_val_kb(m, "Inactive(file): ", pages[LRU_INACTIVE_FILE]);
	show_val_kb(m, "Unevictable:    ", pages[LRU_UNEVICTABLE]);
	show_val_kb(m, "Mlocked:        ", global_zone_page_state(NR_MLOCK));

#ifdef CONFIG_HIGHMEM
	show_val_kb(m, "HighTotal:      ", i.totalhigh);
	show_val_kb(m, "HighFree:       ", i.freehigh);
	show_val_kb(m, "LowTotal:       ", i.totalram - i.totalhigh);
	show_val_kb(m, "LowFree:        ", i.freeram - i.freehigh);
#endif

#ifndef CONFIG_MMU
	show_val_kb(m, "MmapCopy:       ",
		    (unsigned long)atomic_long_read(&mmap_pages_allocated));
#endif

	show_val_kb(m, "SwapTotal:      ", i.totalswap);
	show_val_kb(m, "SwapFree:       ", i.freeswap);
	show_val_kb(m, "Dirty:          ",
		    global_node_page_state(NR_FILE_DIRTY));
	show_val_kb(m, "Writeback:      ",
		    global_node_page_state(NR_WRITEBACK));
	show_val_kb(m, "AnonPages:      ",
		    global_node_page_state(NR_ANON_MAPPED));
	show_val_kb(m, "Mapped:         ",
		    global_node_page_state(NR_FILE_MAPPED));
	show_val_kb(m, "Shmem:          ", i.sharedram);
	show_val_kb(m, "KReclaimable:   ", sreclaimable +
		    global_node_page_state(NR_KERNEL_MISC_RECLAIMABLE));
	show_val_kb(m, "Slab:           ", sreclaimable + sunreclaim);
	show_val_kb(m, "SReclaimable:   ", sreclaimable);
	show_val_kb(m, "SUnreclaim:     ", sunreclaim);
	seq_printf(m, "KernelStack:    %8lu kB\n",
		   global_node_page_state(NR_KERNEL_STACK_KB));
#ifdef CONFIG_SHADOW_CALL_STACK
	seq_printf(m, "ShadowCallStack:%8lu kB\n",
		   global_node_page_state(NR_KERNEL_SCS_KB));
#endif
	show_val_kb(m, "PageTables:     ",
		    global_node_page_state(NR_PAGETABLE));

	show_val_kb(m, "NFS_Unstable:   ", 0);
	show_val_kb(m, "Bounce:         ",
		    global_zone_page_state(NR_BOUNCE));
	show_val_kb(m, "WritebackTmp:   ",
		    global_node_page_state(NR_WRITEBACK_TEMP));
	show_val_kb(m, "CommitLimit:    ", vm_commit_limit());
	show_val_kb(m, "Committed_AS:   ", committed);
	seq_printf(m, "VmallocTotal:   %8lu kB\n",
		   (unsigned long)VMALLOC_TOTAL >> 10);
	show_val_kb(m, "VmallocUsed:    ", vmalloc_nr_pages());
	show_val_kb(m, "VmallocChunk:   ", 0ul);
	show_val_kb(m, "Percpu:         ", pcpu_nr_pages());

#ifdef CONFIG_MEMORY_FAILURE
	seq_printf(m, "HardwareCorrupted: %5lu kB\n",
		   atomic_long_read(&num_poisoned_pages) << (PAGE_SHIFT - 10));
#endif

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
	show_val_kb(m, "AnonHugePages:  ",
		    global_node_page_state(NR_ANON_THPS));
	show_val_kb(m, "ShmemHugePages: ",
		    global_node_page_state(NR_SHMEM_THPS));
	show_val_kb(m, "ShmemPmdMapped: ",
		    global_node_page_state(NR_SHMEM_PMDMAPPED));
	show_val_kb(m, "FileHugePages:  ",
		    global_node_page_state(NR_FILE_THPS));
	show_val_kb(m, "FilePmdMapped:  ",
		    global_node_page_state(NR_FILE_PMDMAPPED));
#endif

#ifdef CONFIG_CMA
	show_val_kb(m, "CmaTotal:       ", totalcma_pages);
	show_val_kb(m, "CmaFree:        ",
		    global_zone_page_state(NR_FREE_CMA_PAGES));
#endif

	hugetlb_report_meminfo(m);

	arch_report_meminfo(m);

	return 0;
}

long si_mem_available(void)
{
	long available;
	unsigned long pagecache;
	unsigned long wmark_low = 0;
	unsigned long pages[NR_LRU_LISTS];
	unsigned long reclaimable;
	struct zone *zone;
	int lru;

	for (lru = LRU_BASE; lru < NR_LRU_LISTS; lru++)
		pages[lru] = global_node_page_state(NR_LRU_BASE + lru);

	for_each_zone(zone)
		wmark_low += low_wmark_pages(zone);

	/*
	 * Estimate the amount of memory available for userspace allocations,
	 * without causing swapping.
	 */
	available = global_zone_page_state(NR_FREE_PAGES) - totalreserve_pages;

	/*
	 * Not all the page cache can be freed, otherwise the system will
	 * start swapping. Assume at least half of the page cache, or the
	 * low watermark worth of cache, needs to stay.
	 */
	pagecache = pages[LRU_ACTIVE_FILE] + pages[LRU_INACTIVE_FILE];
	pagecache -= min(pagecache / 2, wmark_low);
	available += pagecache;

	/*
	 * Part of the reclaimable slab and other kernel memory consists of
	 * items that are in use, and cannot be freed. Cap this estimate at the
	 * low watermark.
	 */
	reclaimable = global_node_page_state_pages(NR_SLAB_RECLAIMABLE_B) +
		global_node_page_state(NR_KERNEL_MISC_RECLAIMABLE);
	available += reclaimable - min(reclaimable / 2, wmark_low);

	if (available < 0)
		available = 0;
	return available;
}
EXPORT_SYMBOL_GPL(si_mem_available);

void si_meminfo(struct sysinfo *val)
{
	val->totalram = totalram_pages();
	val->sharedram = global_node_page_state(NR_SHMEM);
	val->freeram = global_zone_page_state(NR_FREE_PAGES);
	val->bufferram = nr_blockdev_pages();
	val->totalhigh = totalhigh_pages();
	val->freehigh = nr_free_highpages();
	val->mem_unit = PAGE_SIZE;
}