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![Joao Martins](/assets/img/avatar_default.png)
Today with `hugetlb_free_vmemmap=on` the struct page memory that is freed back to page allocator is as following: for a 2M hugetlb page it will reuse the first 4K vmemmap page to remap the remaining 7 vmemmap pages, and for a 1G hugetlb it will remap the remaining 4095 vmemmap pages. Essentially, that means that it breaks the first 4K of a potentially contiguous chunk of memory of 32K (for 2M hugetlb pages) or 16M (for 1G hugetlb pages). For this reason the memory that it's free back to page allocator cannot be used for hugetlb to allocate huge pages of the same size, but rather only of a smaller huge page size: Trying to assign a 64G node to hugetlb (on a 128G 2node guest, each node having 64G): * Before allocation: Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10 ... Node 0, zone Normal, type Movable 340 100 32 15 1 2 0 0 0 1 15558 $ echo 32768 > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages $ cat /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages 31987 * After: Node 0, zone Normal, type Movable 30893 32006 31515 7 0 0 0 0 0 0 0 Notice how the memory freed back are put back into 4K / 8K / 16K page pools. And it allocates a total of 31987 pages (63974M). To fix this behaviour rather than remapping second vmemmap page (thus breaking the contiguous block of memory backing the struct pages) repopulate the first vmemmap page with a new one. We allocate and copy from the currently mapped vmemmap page, and then remap it later on. The same algorithm works if there's a pre initialized walk::reuse_page and the head page doesn't need to be skipped and instead we remap it when the @addr being changed is the @reuse_addr. The new head page is allocated in vmemmap_remap_free() given that on restore there's no need for functional change. Note that, because right now one hugepage is remapped at a time, thus only one free 4K page at a time is needed to remap the head page. Should it fail to allocate said new page, it reuses the one that's already mapped just like before. As a result, for every 64G of contiguous hugepages it can give back 1G more of contiguous memory per 64G, while needing in total 128M new 4K pages (for 2M hugetlb) or 256k (for 1G hugetlb). After the changes, try to assign a 64G node to hugetlb (on a 128G 2node guest, each node with 64G): * Before allocation Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10 ... Node 0, zone Normal, type Movable 1 1 1 0 0 1 0 0 1 1 15564 $ echo 32768 > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages $ cat /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages 32394 * After: Node 0, zone Normal, type Movable 0 50 97 108 96 81 70 46 18 0 0 In the example above, 407 more hugeltb 2M pages are allocated i.e. 814M out of the 32394 (64788M) allocated. So the memory freed back is indeed being used back in hugetlb and there's no massive order-0..order-2 pages accumulated unused. [joao.m.martins@oracle.com: v3] Link: https://lkml.kernel.org/r/20221109200623.96867-1-joao.m.martins@oracle.com [joao.m.martins@oracle.com: add smp_wmb() to ensure page contents are visible prior to PTE write] Link: https://lkml.kernel.org/r/20221110121214.6297-1-joao.m.martins@oracle.com Link: https://lkml.kernel.org/r/20221107153922.77094-1-joao.m.martins@oracle.com Signed-off-by: Joao Martins <joao.m.martins@oracle.com> Reviewed-by: Muchun Song <songmuchun@bytedance.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
608 lines
17 KiB
C
608 lines
17 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* HugeTLB Vmemmap Optimization (HVO)
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*
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* Copyright (c) 2020, ByteDance. All rights reserved.
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*
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* Author: Muchun Song <songmuchun@bytedance.com>
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*
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* See Documentation/mm/vmemmap_dedup.rst
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*/
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#define pr_fmt(fmt) "HugeTLB: " fmt
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#include <linux/pgtable.h>
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#include <linux/moduleparam.h>
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#include <linux/bootmem_info.h>
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#include <asm/pgalloc.h>
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#include <asm/tlbflush.h>
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#include "hugetlb_vmemmap.h"
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/**
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* struct vmemmap_remap_walk - walk vmemmap page table
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*
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* @remap_pte: called for each lowest-level entry (PTE).
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* @nr_walked: the number of walked pte.
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* @reuse_page: the page which is reused for the tail vmemmap pages.
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* @reuse_addr: the virtual address of the @reuse_page page.
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* @vmemmap_pages: the list head of the vmemmap pages that can be freed
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* or is mapped from.
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*/
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struct vmemmap_remap_walk {
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void (*remap_pte)(pte_t *pte, unsigned long addr,
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struct vmemmap_remap_walk *walk);
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unsigned long nr_walked;
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struct page *reuse_page;
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unsigned long reuse_addr;
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struct list_head *vmemmap_pages;
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};
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static int __split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start)
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{
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pmd_t __pmd;
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int i;
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unsigned long addr = start;
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struct page *page = pmd_page(*pmd);
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pte_t *pgtable = pte_alloc_one_kernel(&init_mm);
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if (!pgtable)
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return -ENOMEM;
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pmd_populate_kernel(&init_mm, &__pmd, pgtable);
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for (i = 0; i < PTRS_PER_PTE; i++, addr += PAGE_SIZE) {
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pte_t entry, *pte;
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pgprot_t pgprot = PAGE_KERNEL;
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entry = mk_pte(page + i, pgprot);
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pte = pte_offset_kernel(&__pmd, addr);
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set_pte_at(&init_mm, addr, pte, entry);
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}
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spin_lock(&init_mm.page_table_lock);
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if (likely(pmd_leaf(*pmd))) {
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/*
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* Higher order allocations from buddy allocator must be able to
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* be treated as indepdenent small pages (as they can be freed
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* individually).
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*/
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if (!PageReserved(page))
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split_page(page, get_order(PMD_SIZE));
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/* Make pte visible before pmd. See comment in pmd_install(). */
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smp_wmb();
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pmd_populate_kernel(&init_mm, pmd, pgtable);
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flush_tlb_kernel_range(start, start + PMD_SIZE);
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} else {
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pte_free_kernel(&init_mm, pgtable);
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}
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spin_unlock(&init_mm.page_table_lock);
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return 0;
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}
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static int split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start)
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{
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int leaf;
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spin_lock(&init_mm.page_table_lock);
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leaf = pmd_leaf(*pmd);
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spin_unlock(&init_mm.page_table_lock);
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if (!leaf)
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return 0;
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return __split_vmemmap_huge_pmd(pmd, start);
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}
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static void vmemmap_pte_range(pmd_t *pmd, unsigned long addr,
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unsigned long end,
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struct vmemmap_remap_walk *walk)
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{
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pte_t *pte = pte_offset_kernel(pmd, addr);
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/*
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* The reuse_page is found 'first' in table walk before we start
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* remapping (which is calling @walk->remap_pte).
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*/
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if (!walk->reuse_page) {
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walk->reuse_page = pte_page(*pte);
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/*
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* Because the reuse address is part of the range that we are
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* walking, skip the reuse address range.
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*/
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addr += PAGE_SIZE;
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pte++;
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walk->nr_walked++;
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}
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for (; addr != end; addr += PAGE_SIZE, pte++) {
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walk->remap_pte(pte, addr, walk);
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walk->nr_walked++;
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}
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}
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static int vmemmap_pmd_range(pud_t *pud, unsigned long addr,
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unsigned long end,
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struct vmemmap_remap_walk *walk)
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{
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pmd_t *pmd;
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unsigned long next;
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pmd = pmd_offset(pud, addr);
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do {
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int ret;
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ret = split_vmemmap_huge_pmd(pmd, addr & PMD_MASK);
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if (ret)
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return ret;
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next = pmd_addr_end(addr, end);
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vmemmap_pte_range(pmd, addr, next, walk);
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} while (pmd++, addr = next, addr != end);
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return 0;
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}
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static int vmemmap_pud_range(p4d_t *p4d, unsigned long addr,
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unsigned long end,
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struct vmemmap_remap_walk *walk)
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{
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pud_t *pud;
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unsigned long next;
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pud = pud_offset(p4d, addr);
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do {
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int ret;
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next = pud_addr_end(addr, end);
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ret = vmemmap_pmd_range(pud, addr, next, walk);
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if (ret)
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return ret;
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} while (pud++, addr = next, addr != end);
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return 0;
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}
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static int vmemmap_p4d_range(pgd_t *pgd, unsigned long addr,
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unsigned long end,
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struct vmemmap_remap_walk *walk)
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{
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p4d_t *p4d;
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unsigned long next;
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p4d = p4d_offset(pgd, addr);
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do {
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int ret;
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next = p4d_addr_end(addr, end);
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ret = vmemmap_pud_range(p4d, addr, next, walk);
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if (ret)
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return ret;
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} while (p4d++, addr = next, addr != end);
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return 0;
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}
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static int vmemmap_remap_range(unsigned long start, unsigned long end,
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struct vmemmap_remap_walk *walk)
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{
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unsigned long addr = start;
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unsigned long next;
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pgd_t *pgd;
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VM_BUG_ON(!PAGE_ALIGNED(start));
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VM_BUG_ON(!PAGE_ALIGNED(end));
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pgd = pgd_offset_k(addr);
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do {
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int ret;
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next = pgd_addr_end(addr, end);
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ret = vmemmap_p4d_range(pgd, addr, next, walk);
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if (ret)
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return ret;
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} while (pgd++, addr = next, addr != end);
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flush_tlb_kernel_range(start, end);
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return 0;
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}
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/*
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* Free a vmemmap page. A vmemmap page can be allocated from the memblock
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* allocator or buddy allocator. If the PG_reserved flag is set, it means
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* that it allocated from the memblock allocator, just free it via the
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* free_bootmem_page(). Otherwise, use __free_page().
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*/
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static inline void free_vmemmap_page(struct page *page)
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{
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if (PageReserved(page))
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free_bootmem_page(page);
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else
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__free_page(page);
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}
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/* Free a list of the vmemmap pages */
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static void free_vmemmap_page_list(struct list_head *list)
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{
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struct page *page, *next;
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list_for_each_entry_safe(page, next, list, lru)
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free_vmemmap_page(page);
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}
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static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
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struct vmemmap_remap_walk *walk)
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{
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/*
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* Remap the tail pages as read-only to catch illegal write operation
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* to the tail pages.
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*/
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pgprot_t pgprot = PAGE_KERNEL_RO;
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struct page *page = pte_page(*pte);
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pte_t entry;
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/* Remapping the head page requires r/w */
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if (unlikely(addr == walk->reuse_addr)) {
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pgprot = PAGE_KERNEL;
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list_del(&walk->reuse_page->lru);
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/*
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* Makes sure that preceding stores to the page contents from
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* vmemmap_remap_free() become visible before the set_pte_at()
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* write.
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*/
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smp_wmb();
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}
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entry = mk_pte(walk->reuse_page, pgprot);
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list_add_tail(&page->lru, walk->vmemmap_pages);
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set_pte_at(&init_mm, addr, pte, entry);
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}
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/*
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* How many struct page structs need to be reset. When we reuse the head
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* struct page, the special metadata (e.g. page->flags or page->mapping)
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* cannot copy to the tail struct page structs. The invalid value will be
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* checked in the free_tail_pages_check(). In order to avoid the message
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* of "corrupted mapping in tail page". We need to reset at least 3 (one
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* head struct page struct and two tail struct page structs) struct page
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* structs.
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*/
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#define NR_RESET_STRUCT_PAGE 3
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static inline void reset_struct_pages(struct page *start)
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{
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struct page *from = start + NR_RESET_STRUCT_PAGE;
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BUILD_BUG_ON(NR_RESET_STRUCT_PAGE * 2 > PAGE_SIZE / sizeof(struct page));
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memcpy(start, from, sizeof(*from) * NR_RESET_STRUCT_PAGE);
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}
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static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
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struct vmemmap_remap_walk *walk)
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{
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pgprot_t pgprot = PAGE_KERNEL;
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struct page *page;
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void *to;
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BUG_ON(pte_page(*pte) != walk->reuse_page);
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page = list_first_entry(walk->vmemmap_pages, struct page, lru);
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list_del(&page->lru);
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to = page_to_virt(page);
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copy_page(to, (void *)walk->reuse_addr);
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reset_struct_pages(to);
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/*
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* Makes sure that preceding stores to the page contents become visible
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* before the set_pte_at() write.
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*/
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smp_wmb();
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set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot));
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}
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/**
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* vmemmap_remap_free - remap the vmemmap virtual address range [@start, @end)
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* to the page which @reuse is mapped to, then free vmemmap
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* which the range are mapped to.
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* @start: start address of the vmemmap virtual address range that we want
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* to remap.
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* @end: end address of the vmemmap virtual address range that we want to
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* remap.
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* @reuse: reuse address.
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*
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* Return: %0 on success, negative error code otherwise.
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*/
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static int vmemmap_remap_free(unsigned long start, unsigned long end,
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unsigned long reuse)
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{
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int ret;
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LIST_HEAD(vmemmap_pages);
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struct vmemmap_remap_walk walk = {
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.remap_pte = vmemmap_remap_pte,
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.reuse_addr = reuse,
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.vmemmap_pages = &vmemmap_pages,
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};
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int nid = page_to_nid((struct page *)start);
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gfp_t gfp_mask = GFP_KERNEL | __GFP_THISNODE | __GFP_NORETRY |
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__GFP_NOWARN;
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/*
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* Allocate a new head vmemmap page to avoid breaking a contiguous
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* block of struct page memory when freeing it back to page allocator
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* in free_vmemmap_page_list(). This will allow the likely contiguous
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* struct page backing memory to be kept contiguous and allowing for
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* more allocations of hugepages. Fallback to the currently
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* mapped head page in case should it fail to allocate.
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*/
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walk.reuse_page = alloc_pages_node(nid, gfp_mask, 0);
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if (walk.reuse_page) {
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copy_page(page_to_virt(walk.reuse_page),
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(void *)walk.reuse_addr);
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list_add(&walk.reuse_page->lru, &vmemmap_pages);
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}
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/*
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* In order to make remapping routine most efficient for the huge pages,
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* the routine of vmemmap page table walking has the following rules
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* (see more details from the vmemmap_pte_range()):
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*
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* - The range [@start, @end) and the range [@reuse, @reuse + PAGE_SIZE)
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* should be continuous.
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* - The @reuse address is part of the range [@reuse, @end) that we are
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* walking which is passed to vmemmap_remap_range().
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* - The @reuse address is the first in the complete range.
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*
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* So we need to make sure that @start and @reuse meet the above rules.
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*/
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BUG_ON(start - reuse != PAGE_SIZE);
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mmap_read_lock(&init_mm);
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ret = vmemmap_remap_range(reuse, end, &walk);
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if (ret && walk.nr_walked) {
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end = reuse + walk.nr_walked * PAGE_SIZE;
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/*
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* vmemmap_pages contains pages from the previous
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* vmemmap_remap_range call which failed. These
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* are pages which were removed from the vmemmap.
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* They will be restored in the following call.
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*/
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walk = (struct vmemmap_remap_walk) {
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.remap_pte = vmemmap_restore_pte,
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.reuse_addr = reuse,
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.vmemmap_pages = &vmemmap_pages,
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};
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vmemmap_remap_range(reuse, end, &walk);
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}
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mmap_read_unlock(&init_mm);
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free_vmemmap_page_list(&vmemmap_pages);
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return ret;
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}
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static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
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gfp_t gfp_mask, struct list_head *list)
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{
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unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
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int nid = page_to_nid((struct page *)start);
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struct page *page, *next;
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while (nr_pages--) {
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page = alloc_pages_node(nid, gfp_mask, 0);
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if (!page)
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goto out;
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list_add_tail(&page->lru, list);
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}
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return 0;
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out:
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list_for_each_entry_safe(page, next, list, lru)
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__free_pages(page, 0);
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return -ENOMEM;
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}
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/**
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* vmemmap_remap_alloc - remap the vmemmap virtual address range [@start, end)
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* to the page which is from the @vmemmap_pages
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* respectively.
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* @start: start address of the vmemmap virtual address range that we want
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* to remap.
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* @end: end address of the vmemmap virtual address range that we want to
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* remap.
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* @reuse: reuse address.
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* @gfp_mask: GFP flag for allocating vmemmap pages.
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*
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* Return: %0 on success, negative error code otherwise.
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*/
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static int vmemmap_remap_alloc(unsigned long start, unsigned long end,
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unsigned long reuse, gfp_t gfp_mask)
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{
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LIST_HEAD(vmemmap_pages);
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struct vmemmap_remap_walk walk = {
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.remap_pte = vmemmap_restore_pte,
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.reuse_addr = reuse,
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.vmemmap_pages = &vmemmap_pages,
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};
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/* See the comment in the vmemmap_remap_free(). */
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BUG_ON(start - reuse != PAGE_SIZE);
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if (alloc_vmemmap_page_list(start, end, gfp_mask, &vmemmap_pages))
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return -ENOMEM;
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mmap_read_lock(&init_mm);
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vmemmap_remap_range(reuse, end, &walk);
|
|
mmap_read_unlock(&init_mm);
|
|
|
|
return 0;
|
|
}
|
|
|
|
DEFINE_STATIC_KEY_FALSE(hugetlb_optimize_vmemmap_key);
|
|
EXPORT_SYMBOL(hugetlb_optimize_vmemmap_key);
|
|
|
|
static bool vmemmap_optimize_enabled = IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON);
|
|
core_param(hugetlb_free_vmemmap, vmemmap_optimize_enabled, bool, 0);
|
|
|
|
/**
|
|
* hugetlb_vmemmap_restore - restore previously optimized (by
|
|
* hugetlb_vmemmap_optimize()) vmemmap pages which
|
|
* will be reallocated and remapped.
|
|
* @h: struct hstate.
|
|
* @head: the head page whose vmemmap pages will be restored.
|
|
*
|
|
* Return: %0 if @head's vmemmap pages have been reallocated and remapped,
|
|
* negative error code otherwise.
|
|
*/
|
|
int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head)
|
|
{
|
|
int ret;
|
|
unsigned long vmemmap_start = (unsigned long)head, vmemmap_end;
|
|
unsigned long vmemmap_reuse;
|
|
|
|
if (!HPageVmemmapOptimized(head))
|
|
return 0;
|
|
|
|
vmemmap_end = vmemmap_start + hugetlb_vmemmap_size(h);
|
|
vmemmap_reuse = vmemmap_start;
|
|
vmemmap_start += HUGETLB_VMEMMAP_RESERVE_SIZE;
|
|
|
|
/*
|
|
* The pages which the vmemmap virtual address range [@vmemmap_start,
|
|
* @vmemmap_end) are mapped to are freed to the buddy allocator, and
|
|
* the range is mapped to the page which @vmemmap_reuse is mapped to.
|
|
* When a HugeTLB page is freed to the buddy allocator, previously
|
|
* discarded vmemmap pages must be allocated and remapping.
|
|
*/
|
|
ret = vmemmap_remap_alloc(vmemmap_start, vmemmap_end, vmemmap_reuse,
|
|
GFP_KERNEL | __GFP_NORETRY | __GFP_THISNODE);
|
|
if (!ret) {
|
|
ClearHPageVmemmapOptimized(head);
|
|
static_branch_dec(&hugetlb_optimize_vmemmap_key);
|
|
}
|
|
|
|
return ret;
|
|
}
|
|
|
|
/* Return true iff a HugeTLB whose vmemmap should and can be optimized. */
|
|
static bool vmemmap_should_optimize(const struct hstate *h, const struct page *head)
|
|
{
|
|
if (!READ_ONCE(vmemmap_optimize_enabled))
|
|
return false;
|
|
|
|
if (!hugetlb_vmemmap_optimizable(h))
|
|
return false;
|
|
|
|
if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) {
|
|
pmd_t *pmdp, pmd;
|
|
struct page *vmemmap_page;
|
|
unsigned long vaddr = (unsigned long)head;
|
|
|
|
/*
|
|
* Only the vmemmap page's vmemmap page can be self-hosted.
|
|
* Walking the page tables to find the backing page of the
|
|
* vmemmap page.
|
|
*/
|
|
pmdp = pmd_off_k(vaddr);
|
|
/*
|
|
* The READ_ONCE() is used to stabilize *pmdp in a register or
|
|
* on the stack so that it will stop changing under the code.
|
|
* The only concurrent operation where it can be changed is
|
|
* split_vmemmap_huge_pmd() (*pmdp will be stable after this
|
|
* operation).
|
|
*/
|
|
pmd = READ_ONCE(*pmdp);
|
|
if (pmd_leaf(pmd))
|
|
vmemmap_page = pmd_page(pmd) + pte_index(vaddr);
|
|
else
|
|
vmemmap_page = pte_page(*pte_offset_kernel(pmdp, vaddr));
|
|
/*
|
|
* Due to HugeTLB alignment requirements and the vmemmap pages
|
|
* being at the start of the hotplugged memory region in
|
|
* memory_hotplug.memmap_on_memory case. Checking any vmemmap
|
|
* page's vmemmap page if it is marked as VmemmapSelfHosted is
|
|
* sufficient.
|
|
*
|
|
* [ hotplugged memory ]
|
|
* [ section ][...][ section ]
|
|
* [ vmemmap ][ usable memory ]
|
|
* ^ | | |
|
|
* +---+ | |
|
|
* ^ | |
|
|
* +-------+ |
|
|
* ^ |
|
|
* +-------------------------------------------+
|
|
*/
|
|
if (PageVmemmapSelfHosted(vmemmap_page))
|
|
return false;
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
/**
|
|
* hugetlb_vmemmap_optimize - optimize @head page's vmemmap pages.
|
|
* @h: struct hstate.
|
|
* @head: the head page whose vmemmap pages will be optimized.
|
|
*
|
|
* This function only tries to optimize @head's vmemmap pages and does not
|
|
* guarantee that the optimization will succeed after it returns. The caller
|
|
* can use HPageVmemmapOptimized(@head) to detect if @head's vmemmap pages
|
|
* have been optimized.
|
|
*/
|
|
void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
|
|
{
|
|
unsigned long vmemmap_start = (unsigned long)head, vmemmap_end;
|
|
unsigned long vmemmap_reuse;
|
|
|
|
if (!vmemmap_should_optimize(h, head))
|
|
return;
|
|
|
|
static_branch_inc(&hugetlb_optimize_vmemmap_key);
|
|
|
|
vmemmap_end = vmemmap_start + hugetlb_vmemmap_size(h);
|
|
vmemmap_reuse = vmemmap_start;
|
|
vmemmap_start += HUGETLB_VMEMMAP_RESERVE_SIZE;
|
|
|
|
/*
|
|
* Remap the vmemmap virtual address range [@vmemmap_start, @vmemmap_end)
|
|
* to the page which @vmemmap_reuse is mapped to, then free the pages
|
|
* which the range [@vmemmap_start, @vmemmap_end] is mapped to.
|
|
*/
|
|
if (vmemmap_remap_free(vmemmap_start, vmemmap_end, vmemmap_reuse))
|
|
static_branch_dec(&hugetlb_optimize_vmemmap_key);
|
|
else
|
|
SetHPageVmemmapOptimized(head);
|
|
}
|
|
|
|
static struct ctl_table hugetlb_vmemmap_sysctls[] = {
|
|
{
|
|
.procname = "hugetlb_optimize_vmemmap",
|
|
.data = &vmemmap_optimize_enabled,
|
|
.maxlen = sizeof(int),
|
|
.mode = 0644,
|
|
.proc_handler = proc_dobool,
|
|
},
|
|
{ }
|
|
};
|
|
|
|
static int __init hugetlb_vmemmap_init(void)
|
|
{
|
|
/* HUGETLB_VMEMMAP_RESERVE_SIZE should cover all used struct pages */
|
|
BUILD_BUG_ON(__NR_USED_SUBPAGE * sizeof(struct page) > HUGETLB_VMEMMAP_RESERVE_SIZE);
|
|
|
|
if (IS_ENABLED(CONFIG_PROC_SYSCTL)) {
|
|
const struct hstate *h;
|
|
|
|
for_each_hstate(h) {
|
|
if (hugetlb_vmemmap_optimizable(h)) {
|
|
register_sysctl_init("vm", hugetlb_vmemmap_sysctls);
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
return 0;
|
|
}
|
|
late_initcall(hugetlb_vmemmap_init);
|