Merge tag 'for-4.15-rc7-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave...

[mirror_ubuntu-bionic-kernel.git] / mm / bootmem.c

// SPDX-License-Identifier: GPL-2.0
/*
 *  bootmem - A boot-time physical memory allocator and configurator
 *
 *  Copyright (C) 1999 Ingo Molnar
 *                1999 Kanoj Sarcar, SGI
 *                2008 Johannes Weiner
 *
 * Access to this subsystem has to be serialized externally (which is true
 * for the boot process anyway).
 */
#include <linux/init.h>
#include <linux/pfn.h>
#include <linux/slab.h>
#include <linux/export.h>
#include <linux/kmemleak.h>
#include <linux/range.h>
#include <linux/bug.h>
#include <linux/io.h>
#include <linux/bootmem.h>

#include "internal.h"

#ifndef CONFIG_NEED_MULTIPLE_NODES
struct pglist_data __refdata contig_page_data = {
        .bdata = &bootmem_node_data[0]
};
EXPORT_SYMBOL(contig_page_data);
#endif

unsigned long max_low_pfn;
unsigned long min_low_pfn;
unsigned long max_pfn;
unsigned long long max_possible_pfn;

bootmem_data_t bootmem_node_data[MAX_NUMNODES] __initdata;

static struct list_head bdata_list __initdata = LIST_HEAD_INIT(bdata_list);

static int bootmem_debug;

static int __init bootmem_debug_setup(char *buf)
{
        bootmem_debug = 1;
        return 0;
}
early_param("bootmem_debug", bootmem_debug_setup);

#define bdebug(fmt, args...) ({                         \
        if (unlikely(bootmem_debug))                    \
                pr_info("bootmem::%s " fmt,             \
                        __func__, ## args);             \
})

static unsigned long __init bootmap_bytes(unsigned long pages)
{
        unsigned long bytes = DIV_ROUND_UP(pages, BITS_PER_BYTE);

        return ALIGN(bytes, sizeof(long));
}

/**
 * bootmem_bootmap_pages - calculate bitmap size in pages
 * @pages: number of pages the bitmap has to represent
 */
unsigned long __init bootmem_bootmap_pages(unsigned long pages)
{
        unsigned long bytes = bootmap_bytes(pages);

        return PAGE_ALIGN(bytes) >> PAGE_SHIFT;
}

/*
 * link bdata in order
 */
static void __init link_bootmem(bootmem_data_t *bdata)
{
        bootmem_data_t *ent;

        list_for_each_entry(ent, &bdata_list, list) {
                if (bdata->node_min_pfn < ent->node_min_pfn) {
                        list_add_tail(&bdata->list, &ent->list);
                        return;
                }
        }

        list_add_tail(&bdata->list, &bdata_list);
}

/*
 * Called once to set up the allocator itself.
 */
static unsigned long __init init_bootmem_core(bootmem_data_t *bdata,
        unsigned long mapstart, unsigned long start, unsigned long end)
{
        unsigned long mapsize;

        mminit_validate_memmodel_limits(&start, &end);
        bdata->node_bootmem_map = phys_to_virt(PFN_PHYS(mapstart));
        bdata->node_min_pfn = start;
        bdata->node_low_pfn = end;
        link_bootmem(bdata);

        /*
         * Initially all pages are reserved - setup_arch() has to
         * register free RAM areas explicitly.
         */
        mapsize = bootmap_bytes(end - start);
        memset(bdata->node_bootmem_map, 0xff, mapsize);

        bdebug("nid=%td start=%lx map=%lx end=%lx mapsize=%lx\n",
                bdata - bootmem_node_data, start, mapstart, end, mapsize);

        return mapsize;
}

/**
 * init_bootmem_node - register a node as boot memory
 * @pgdat: node to register
 * @freepfn: pfn where the bitmap for this node is to be placed
 * @startpfn: first pfn on the node
 * @endpfn: first pfn after the node
 *
 * Returns the number of bytes needed to hold the bitmap for this node.
 */
unsigned long __init init_bootmem_node(pg_data_t *pgdat, unsigned long freepfn,
                                unsigned long startpfn, unsigned long endpfn)
{
        return init_bootmem_core(pgdat->bdata, freepfn, startpfn, endpfn);
}

/**
 * init_bootmem - register boot memory
 * @start: pfn where the bitmap is to be placed
 * @pages: number of available physical pages
 *
 * Returns the number of bytes needed to hold the bitmap.
 */
unsigned long __init init_bootmem(unsigned long start, unsigned long pages)
{
        max_low_pfn = pages;
        min_low_pfn = start;
        return init_bootmem_core(NODE_DATA(0)->bdata, start, 0, pages);
}

/*
 * free_bootmem_late - free bootmem pages directly to page allocator
 * @addr: starting physical address of the range
 * @size: size of the range in bytes
 *
 * This is only useful when the bootmem allocator has already been torn
 * down, but we are still initializing the system.  Pages are given directly
 * to the page allocator, no bootmem metadata is updated because it is gone.
 */
void __init free_bootmem_late(unsigned long physaddr, unsigned long size)
{
        unsigned long cursor, end;

        kmemleak_free_part_phys(physaddr, size);

        cursor = PFN_UP(physaddr);
        end = PFN_DOWN(physaddr + size);

        for (; cursor < end; cursor++) {
                __free_pages_bootmem(pfn_to_page(cursor), cursor, 0);
                totalram_pages++;
        }
}

static unsigned long __init free_all_bootmem_core(bootmem_data_t *bdata)
{
        struct page *page;
        unsigned long *map, start, end, pages, cur, count = 0;

        if (!bdata->node_bootmem_map)
                return 0;

        map = bdata->node_bootmem_map;
        start = bdata->node_min_pfn;
        end = bdata->node_low_pfn;

        bdebug("nid=%td start=%lx end=%lx\n",
                bdata - bootmem_node_data, start, end);

        while (start < end) {
                unsigned long idx, vec;
                unsigned shift;

                idx = start - bdata->node_min_pfn;
                shift = idx & (BITS_PER_LONG - 1);
                /*
                 * vec holds at most BITS_PER_LONG map bits,
                 * bit 0 corresponds to start.
                 */
                vec = ~map[idx / BITS_PER_LONG];

                if (shift) {
                        vec >>= shift;
                        if (end - start >= BITS_PER_LONG)
                                vec |= ~map[idx / BITS_PER_LONG + 1] <<
                                        (BITS_PER_LONG - shift);
                }
                /*
                 * If we have a properly aligned and fully unreserved
                 * BITS_PER_LONG block of pages in front of us, free
                 * it in one go.
                 */
                if (IS_ALIGNED(start, BITS_PER_LONG) && vec == ~0UL) {
                        int order = ilog2(BITS_PER_LONG);

                        __free_pages_bootmem(pfn_to_page(start), start, order);
                        count += BITS_PER_LONG;
                        start += BITS_PER_LONG;
                } else {
                        cur = start;

                        start = ALIGN(start + 1, BITS_PER_LONG);
                        while (vec && cur != start) {
                                if (vec & 1) {
                                        page = pfn_to_page(cur);
                                        __free_pages_bootmem(page, cur, 0);
                                        count++;
                                }
                                vec >>= 1;
                                ++cur;
                        }
                }
        }

        cur = bdata->node_min_pfn;
        page = virt_to_page(bdata->node_bootmem_map);
        pages = bdata->node_low_pfn - bdata->node_min_pfn;
        pages = bootmem_bootmap_pages(pages);
        count += pages;
        while (pages--)
                __free_pages_bootmem(page++, cur++, 0);
        bdata->node_bootmem_map = NULL;

        bdebug("nid=%td released=%lx\n", bdata - bootmem_node_data, count);

        return count;
}

static int reset_managed_pages_done __initdata;

void reset_node_managed_pages(pg_data_t *pgdat)
{
        struct zone *z;

        for (z = pgdat->node_zones; z < pgdat->node_zones + MAX_NR_ZONES; z++)
                z->managed_pages = 0;
}

void __init reset_all_zones_managed_pages(void)
{
        struct pglist_data *pgdat;

        if (reset_managed_pages_done)
                return;

        for_each_online_pgdat(pgdat)
                reset_node_managed_pages(pgdat);

        reset_managed_pages_done = 1;
}

/**
 * free_all_bootmem - release free pages to the buddy allocator
 *
 * Returns the number of pages actually released.
 */
unsigned long __init free_all_bootmem(void)
{
        unsigned long total_pages = 0;
        bootmem_data_t *bdata;

        reset_all_zones_managed_pages();

        list_for_each_entry(bdata, &bdata_list, list)
                total_pages += free_all_bootmem_core(bdata);

        totalram_pages += total_pages;

        return total_pages;
}

static void __init __free(bootmem_data_t *bdata,
                        unsigned long sidx, unsigned long eidx)
{
        unsigned long idx;

        bdebug("nid=%td start=%lx end=%lx\n", bdata - bootmem_node_data,
                sidx + bdata->node_min_pfn,
                eidx + bdata->node_min_pfn);

        if (WARN_ON(bdata->node_bootmem_map == NULL))
                return;

        if (bdata->hint_idx > sidx)
                bdata->hint_idx = sidx;

        for (idx = sidx; idx < eidx; idx++)
                if (!test_and_clear_bit(idx, bdata->node_bootmem_map))
                        BUG();
}

static int __init __reserve(bootmem_data_t *bdata, unsigned long sidx,
                        unsigned long eidx, int flags)
{
        unsigned long idx;
        int exclusive = flags & BOOTMEM_EXCLUSIVE;

        bdebug("nid=%td start=%lx end=%lx flags=%x\n",
                bdata - bootmem_node_data,
                sidx + bdata->node_min_pfn,
                eidx + bdata->node_min_pfn,
                flags);

        if (WARN_ON(bdata->node_bootmem_map == NULL))
                return 0;

        for (idx = sidx; idx < eidx; idx++)
                if (test_and_set_bit(idx, bdata->node_bootmem_map)) {
                        if (exclusive) {
                                __free(bdata, sidx, idx);
                                return -EBUSY;
                        }
                        bdebug("silent double reserve of PFN %lx\n",
                                idx + bdata->node_min_pfn);
                }
        return 0;
}

static int __init mark_bootmem_node(bootmem_data_t *bdata,
                                unsigned long start, unsigned long end,
                                int reserve, int flags)
{
        unsigned long sidx, eidx;

        bdebug("nid=%td start=%lx end=%lx reserve=%d flags=%x\n",
                bdata - bootmem_node_data, start, end, reserve, flags);

        BUG_ON(start < bdata->node_min_pfn);
        BUG_ON(end > bdata->node_low_pfn);

        sidx = start - bdata->node_min_pfn;
        eidx = end - bdata->node_min_pfn;

        if (reserve)
                return __reserve(bdata, sidx, eidx, flags);
        else
                __free(bdata, sidx, eidx);
        return 0;
}

static int __init mark_bootmem(unsigned long start, unsigned long end,
                                int reserve, int flags)
{
        unsigned long pos;
        bootmem_data_t *bdata;

        pos = start;
        list_for_each_entry(bdata, &bdata_list, list) {
                int err;
                unsigned long max;

                if (pos < bdata->node_min_pfn ||
                    pos >= bdata->node_low_pfn) {
                        BUG_ON(pos != start);
                        continue;
                }

                max = min(bdata->node_low_pfn, end);

                err = mark_bootmem_node(bdata, pos, max, reserve, flags);
                if (reserve && err) {
                        mark_bootmem(start, pos, 0, 0);
                        return err;
                }

                if (max == end)
                        return 0;
                pos = bdata->node_low_pfn;
        }
        BUG();
}

/**
 * free_bootmem_node - mark a page range as usable
 * @pgdat: node the range resides on
 * @physaddr: starting address of the range
 * @size: size of the range in bytes
 *
 * Partial pages will be considered reserved and left as they are.
 *
 * The range must reside completely on the specified node.
 */
void __init free_bootmem_node(pg_data_t *pgdat, unsigned long physaddr,
                              unsigned long size)
{
        unsigned long start, end;

        kmemleak_free_part_phys(physaddr, size);

        start = PFN_UP(physaddr);
        end = PFN_DOWN(physaddr + size);

        mark_bootmem_node(pgdat->bdata, start, end, 0, 0);
}

/**
 * free_bootmem - mark a page range as usable
 * @addr: starting physical address of the range
 * @size: size of the range in bytes
 *
 * Partial pages will be considered reserved and left as they are.
 *
 * The range must be contiguous but may span node boundaries.
 */
void __init free_bootmem(unsigned long physaddr, unsigned long size)
{
        unsigned long start, end;

        kmemleak_free_part_phys(physaddr, size);

        start = PFN_UP(physaddr);
        end = PFN_DOWN(physaddr + size);

        mark_bootmem(start, end, 0, 0);
}

/**
 * reserve_bootmem_node - mark a page range as reserved
 * @pgdat: node the range resides on
 * @physaddr: starting address of the range
 * @size: size of the range in bytes
 * @flags: reservation flags (see linux/bootmem.h)
 *
 * Partial pages will be reserved.
 *
 * The range must reside completely on the specified node.
 */
int __init reserve_bootmem_node(pg_data_t *pgdat, unsigned long physaddr,
                                 unsigned long size, int flags)
{
        unsigned long start, end;

        start = PFN_DOWN(physaddr);
        end = PFN_UP(physaddr + size);

        return mark_bootmem_node(pgdat->bdata, start, end, 1, flags);
}

/**
 * reserve_bootmem - mark a page range as reserved
 * @addr: starting address of the range
 * @size: size of the range in bytes
 * @flags: reservation flags (see linux/bootmem.h)
 *
 * Partial pages will be reserved.
 *
 * The range must be contiguous but may span node boundaries.
 */
int __init reserve_bootmem(unsigned long addr, unsigned long size,
                            int flags)
{
        unsigned long start, end;

        start = PFN_DOWN(addr);
        end = PFN_UP(addr + size);

        return mark_bootmem(start, end, 1, flags);
}

static unsigned long __init align_idx(struct bootmem_data *bdata,
                                      unsigned long idx, unsigned long step)
{
        unsigned long base = bdata->node_min_pfn;

        /*
         * Align the index with respect to the node start so that the
         * combination of both satisfies the requested alignment.
         */

        return ALIGN(base + idx, step) - base;
}

static unsigned long __init align_off(struct bootmem_data *bdata,
                                      unsigned long off, unsigned long align)
{
        unsigned long base = PFN_PHYS(bdata->node_min_pfn);

        /* Same as align_idx for byte offsets */

        return ALIGN(base + off, align) - base;
}

static void * __init alloc_bootmem_bdata(struct bootmem_data *bdata,
                                        unsigned long size, unsigned long align,
                                        unsigned long goal, unsigned long limit)
{
        unsigned long fallback = 0;
        unsigned long min, max, start, sidx, midx, step;

        bdebug("nid=%td size=%lx [%lu pages] align=%lx goal=%lx limit=%lx\n",
                bdata - bootmem_node_data, size, PAGE_ALIGN(size) >> PAGE_SHIFT,
                align, goal, limit);

        BUG_ON(!size);
        BUG_ON(align & (align - 1));
        BUG_ON(limit && goal + size > limit);

        if (!bdata->node_bootmem_map)
                return NULL;

        min = bdata->node_min_pfn;
        max = bdata->node_low_pfn;

        goal >>= PAGE_SHIFT;
        limit >>= PAGE_SHIFT;

        if (limit && max > limit)
                max = limit;
        if (max <= min)
                return NULL;

        step = max(align >> PAGE_SHIFT, 1UL);

        if (goal && min < goal && goal < max)
                start = ALIGN(goal, step);
        else
                start = ALIGN(min, step);

        sidx = start - bdata->node_min_pfn;
        midx = max - bdata->node_min_pfn;

        if (bdata->hint_idx > sidx) {
                /*
                 * Handle the valid case of sidx being zero and still
                 * catch the fallback below.
                 */
                fallback = sidx + 1;
                sidx = align_idx(bdata, bdata->hint_idx, step);
        }

        while (1) {
                int merge;
                void *region;
                unsigned long eidx, i, start_off, end_off;
find_block:
                sidx = find_next_zero_bit(bdata->node_bootmem_map, midx, sidx);
                sidx = align_idx(bdata, sidx, step);
                eidx = sidx + PFN_UP(size);

                if (sidx >= midx || eidx > midx)
                        break;

                for (i = sidx; i < eidx; i++)
                        if (test_bit(i, bdata->node_bootmem_map)) {
                                sidx = align_idx(bdata, i, step);
                                if (sidx == i)
                                        sidx += step;
                                goto find_block;
                        }

                if (bdata->last_end_off & (PAGE_SIZE - 1) &&
                                PFN_DOWN(bdata->last_end_off) + 1 == sidx)
                        start_off = align_off(bdata, bdata->last_end_off, align);
                else
                        start_off = PFN_PHYS(sidx);

                merge = PFN_DOWN(start_off) < sidx;
                end_off = start_off + size;

                bdata->last_end_off = end_off;
                bdata->hint_idx = PFN_UP(end_off);

                /*
                 * Reserve the area now:
                 */
                if (__reserve(bdata, PFN_DOWN(start_off) + merge,
                                PFN_UP(end_off), BOOTMEM_EXCLUSIVE))
                        BUG();

                region = phys_to_virt(PFN_PHYS(bdata->node_min_pfn) +
                                start_off);
                memset(region, 0, size);
                /*
                 * The min_count is set to 0 so that bootmem allocated blocks
                 * are never reported as leaks.
                 */
                kmemleak_alloc(region, size, 0, 0);
                return region;
        }

        if (fallback) {
                sidx = align_idx(bdata, fallback - 1, step);
                fallback = 0;
                goto find_block;
        }

        return NULL;
}

static void * __init alloc_bootmem_core(unsigned long size,
                                        unsigned long align,
                                        unsigned long goal,
                                        unsigned long limit)
{
        bootmem_data_t *bdata;
        void *region;

        if (WARN_ON_ONCE(slab_is_available()))
                return kzalloc(size, GFP_NOWAIT);

        list_for_each_entry(bdata, &bdata_list, list) {
                if (goal && bdata->node_low_pfn <= PFN_DOWN(goal))
                        continue;
                if (limit && bdata->node_min_pfn >= PFN_DOWN(limit))
                        break;

                region = alloc_bootmem_bdata(bdata, size, align, goal, limit);
                if (region)
                        return region;
        }

        return NULL;
}

static void * __init ___alloc_bootmem_nopanic(unsigned long size,
                                              unsigned long align,
                                              unsigned long goal,
                                              unsigned long limit)
{
        void *ptr;

restart:
        ptr = alloc_bootmem_core(size, align, goal, limit);
        if (ptr)
                return ptr;
        if (goal) {
                goal = 0;
                goto restart;
        }

        return NULL;
}

/**
 * __alloc_bootmem_nopanic - allocate boot memory without panicking
 * @size: size of the request in bytes
 * @align: alignment of the region
 * @goal: preferred starting address of the region
 *
 * The goal is dropped if it can not be satisfied and the allocation will
 * fall back to memory below @goal.
 *
 * Allocation may happen on any node in the system.
 *
 * Returns NULL on failure.
 */
void * __init __alloc_bootmem_nopanic(unsigned long size, unsigned long align,
                                        unsigned long goal)
{
        unsigned long limit = 0;

        return ___alloc_bootmem_nopanic(size, align, goal, limit);
}

static void * __init ___alloc_bootmem(unsigned long size, unsigned long align,
                                        unsigned long goal, unsigned long limit)
{
        void *mem = ___alloc_bootmem_nopanic(size, align, goal, limit);

        if (mem)
                return mem;
        /*
         * Whoops, we cannot satisfy the allocation request.
         */
        pr_alert("bootmem alloc of %lu bytes failed!\n", size);
        panic("Out of memory");
        return NULL;
}

/**
 * __alloc_bootmem - allocate boot memory
 * @size: size of the request in bytes
 * @align: alignment of the region
 * @goal: preferred starting address of the region
 *
 * The goal is dropped if it can not be satisfied and the allocation will
 * fall back to memory below @goal.
 *
 * Allocation may happen on any node in the system.
 *
 * The function panics if the request can not be satisfied.
 */
void * __init __alloc_bootmem(unsigned long size, unsigned long align,
                              unsigned long goal)
{
        unsigned long limit = 0;

        return ___alloc_bootmem(size, align, goal, limit);
}

void * __init ___alloc_bootmem_node_nopanic(pg_data_t *pgdat,
                                unsigned long size, unsigned long align,
                                unsigned long goal, unsigned long limit)
{
        void *ptr;

        if (WARN_ON_ONCE(slab_is_available()))
                return kzalloc_node(size, GFP_NOWAIT, pgdat->node_id);
again:

        /* do not panic in alloc_bootmem_bdata() */
        if (limit && goal + size > limit)
                limit = 0;

        ptr = alloc_bootmem_bdata(pgdat->bdata, size, align, goal, limit);
        if (ptr)
                return ptr;

        ptr = alloc_bootmem_core(size, align, goal, limit);
        if (ptr)
                return ptr;

        if (goal) {
                goal = 0;
                goto again;
        }

        return NULL;
}

void * __init __alloc_bootmem_node_nopanic(pg_data_t *pgdat, unsigned long size,
                                   unsigned long align, unsigned long goal)
{
        return ___alloc_bootmem_node_nopanic(pgdat, size, align, goal, 0);
}

void * __init ___alloc_bootmem_node(pg_data_t *pgdat, unsigned long size,
                                    unsigned long align, unsigned long goal,
                                    unsigned long limit)
{
        void *ptr;

        ptr = ___alloc_bootmem_node_nopanic(pgdat, size, align, goal, 0);
        if (ptr)
                return ptr;

        pr_alert("bootmem alloc of %lu bytes failed!\n", size);
        panic("Out of memory");
        return NULL;
}

/**
 * __alloc_bootmem_node - allocate boot memory from a specific node
 * @pgdat: node to allocate from
 * @size: size of the request in bytes
 * @align: alignment of the region
 * @goal: preferred starting address of the region
 *
 * The goal is dropped if it can not be satisfied and the allocation will
 * fall back to memory below @goal.
 *
 * Allocation may fall back to any node in the system if the specified node
 * can not hold the requested memory.
 *
 * The function panics if the request can not be satisfied.
 */
void * __init __alloc_bootmem_node(pg_data_t *pgdat, unsigned long size,
                                   unsigned long align, unsigned long goal)
{
        if (WARN_ON_ONCE(slab_is_available()))
                return kzalloc_node(size, GFP_NOWAIT, pgdat->node_id);

        return  ___alloc_bootmem_node(pgdat, size, align, goal, 0);
}

void * __init __alloc_bootmem_node_high(pg_data_t *pgdat, unsigned long size,
                                   unsigned long align, unsigned long goal)
{
#ifdef MAX_DMA32_PFN
        unsigned long end_pfn;

        if (WARN_ON_ONCE(slab_is_available()))
                return kzalloc_node(size, GFP_NOWAIT, pgdat->node_id);

        /* update goal according ...MAX_DMA32_PFN */
        end_pfn = pgdat_end_pfn(pgdat);

        if (end_pfn > MAX_DMA32_PFN + (128 >> (20 - PAGE_SHIFT)) &&
            (goal >> PAGE_SHIFT) < MAX_DMA32_PFN) {
                void *ptr;
                unsigned long new_goal;

                new_goal = MAX_DMA32_PFN << PAGE_SHIFT;
                ptr = alloc_bootmem_bdata(pgdat->bdata, size, align,
                                                 new_goal, 0);
                if (ptr)
                        return ptr;
        }
#endif

        return __alloc_bootmem_node(pgdat, size, align, goal);

}

/**
 * __alloc_bootmem_low - allocate low boot memory
 * @size: size of the request in bytes
 * @align: alignment of the region
 * @goal: preferred starting address of the region
 *
 * The goal is dropped if it can not be satisfied and the allocation will
 * fall back to memory below @goal.
 *
 * Allocation may happen on any node in the system.
 *
 * The function panics if the request can not be satisfied.
 */
void * __init __alloc_bootmem_low(unsigned long size, unsigned long align,
                                  unsigned long goal)
{
        return ___alloc_bootmem(size, align, goal, ARCH_LOW_ADDRESS_LIMIT);
}

void * __init __alloc_bootmem_low_nopanic(unsigned long size,
                                          unsigned long align,
                                          unsigned long goal)
{
        return ___alloc_bootmem_nopanic(size, align, goal,
                                        ARCH_LOW_ADDRESS_LIMIT);
}

/**
 * __alloc_bootmem_low_node - allocate low boot memory from a specific node
 * @pgdat: node to allocate from
 * @size: size of the request in bytes
 * @align: alignment of the region
 * @goal: preferred starting address of the region
 *
 * The goal is dropped if it can not be satisfied and the allocation will
 * fall back to memory below @goal.
 *
 * Allocation may fall back to any node in the system if the specified node
 * can not hold the requested memory.
 *
 * The function panics if the request can not be satisfied.
 */
void * __init __alloc_bootmem_low_node(pg_data_t *pgdat, unsigned long size,
                                       unsigned long align, unsigned long goal)
{
        if (WARN_ON_ONCE(slab_is_available()))
                return kzalloc_node(size, GFP_NOWAIT, pgdat->node_id);

        return ___alloc_bootmem_node(pgdat, size, align,
                                     goal, ARCH_LOW_ADDRESS_LIMIT);
}