/* * PPC Huge TLB Page Support for Kernel. * * Copyright (C) 2003 David Gibson, IBM Corporation. * Copyright (C) 2011 Becky Bruce, Freescale Semiconductor * * Based on the IA-32 version: * Copyright (C) 2002, Rohit Seth */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #ifdef CONFIG_HUGETLB_PAGE #define PAGE_SHIFT_64K 16 #define PAGE_SHIFT_512K 19 #define PAGE_SHIFT_8M 23 #define PAGE_SHIFT_16M 24 #define PAGE_SHIFT_16G 34 unsigned int HPAGE_SHIFT; EXPORT_SYMBOL(HPAGE_SHIFT); #define hugepd_none(hpd) (hpd_val(hpd) == 0) pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr, unsigned long sz) { /* * Only called for hugetlbfs pages, hence can ignore THP and the * irq disabled walk. */ return __find_linux_pte(mm->pgd, addr, NULL, NULL); } static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp, unsigned long address, unsigned pdshift, unsigned pshift) { struct kmem_cache *cachep; pte_t *new; int i; int num_hugepd; if (pshift >= pdshift) { cachep = hugepte_cache; num_hugepd = 1 << (pshift - pdshift); } else { cachep = PGT_CACHE(pdshift - pshift); num_hugepd = 1; } new = kmem_cache_zalloc(cachep, pgtable_gfp_flags(mm, GFP_KERNEL)); BUG_ON(pshift > HUGEPD_SHIFT_MASK); BUG_ON((unsigned long)new & HUGEPD_SHIFT_MASK); if (! new) return -ENOMEM; /* * Make sure other cpus find the hugepd set only after a * properly initialized page table is visible to them. * For more details look for comment in __pte_alloc(). */ smp_wmb(); spin_lock(&mm->page_table_lock); /* * We have multiple higher-level entries that point to the same * actual pte location. Fill in each as we go and backtrack on error. * We need all of these so the DTLB pgtable walk code can find the * right higher-level entry without knowing if it's a hugepage or not. */ for (i = 0; i < num_hugepd; i++, hpdp++) { if (unlikely(!hugepd_none(*hpdp))) break; else { #ifdef CONFIG_PPC_BOOK3S_64 *hpdp = __hugepd(__pa(new) | (shift_to_mmu_psize(pshift) << 2)); #elif defined(CONFIG_PPC_8xx) *hpdp = __hugepd(__pa(new) | _PMD_USER | (pshift == PAGE_SHIFT_8M ? _PMD_PAGE_8M : _PMD_PAGE_512K) | _PMD_PRESENT); #else /* We use the old format for PPC_FSL_BOOK3E */ *hpdp = __hugepd(((unsigned long)new & ~PD_HUGE) | pshift); #endif } } /* If we bailed from the for loop early, an error occurred, clean up */ if (i < num_hugepd) { for (i = i - 1 ; i >= 0; i--, hpdp--) *hpdp = __hugepd(0); kmem_cache_free(cachep, new); } spin_unlock(&mm->page_table_lock); return 0; } /* * These macros define how to determine which level of the page table holds * the hpdp. */ #if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_8xx) #define HUGEPD_PGD_SHIFT PGDIR_SHIFT #define HUGEPD_PUD_SHIFT PUD_SHIFT #else #define HUGEPD_PGD_SHIFT PUD_SHIFT #define HUGEPD_PUD_SHIFT PMD_SHIFT #endif /* * At this point we do the placement change only for BOOK3S 64. This would * possibly work on other subarchs. */ pte_t *huge_pte_alloc(struct mm_struct *mm, unsigned long addr, unsigned long sz) { pgd_t *pg; pud_t *pu; pmd_t *pm; hugepd_t *hpdp = NULL; unsigned pshift = __ffs(sz); unsigned pdshift = PGDIR_SHIFT; addr &= ~(sz-1); pg = pgd_offset(mm, addr); #ifdef CONFIG_PPC_BOOK3S_64 if (pshift == PGDIR_SHIFT) /* 16GB huge page */ return (pte_t *) pg; else if (pshift > PUD_SHIFT) /* * We need to use hugepd table */ hpdp = (hugepd_t *)pg; else { pdshift = PUD_SHIFT; pu = pud_alloc(mm, pg, addr); if (pshift == PUD_SHIFT) return (pte_t *)pu; else if (pshift > PMD_SHIFT) hpdp = (hugepd_t *)pu; else { pdshift = PMD_SHIFT; pm = pmd_alloc(mm, pu, addr); if (pshift == PMD_SHIFT) /* 16MB hugepage */ return (pte_t *)pm; else hpdp = (hugepd_t *)pm; } } #else if (pshift >= HUGEPD_PGD_SHIFT) { hpdp = (hugepd_t *)pg; } else { pdshift = PUD_SHIFT; pu = pud_alloc(mm, pg, addr); if (pshift >= HUGEPD_PUD_SHIFT) { hpdp = (hugepd_t *)pu; } else { pdshift = PMD_SHIFT; pm = pmd_alloc(mm, pu, addr); hpdp = (hugepd_t *)pm; } } #endif if (!hpdp) return NULL; BUG_ON(!hugepd_none(*hpdp) && !hugepd_ok(*hpdp)); if (hugepd_none(*hpdp) && __hugepte_alloc(mm, hpdp, addr, pdshift, pshift)) return NULL; return hugepte_offset(*hpdp, addr, pdshift); } #ifdef CONFIG_PPC_BOOK3S_64 /* * Tracks gpages after the device tree is scanned and before the * huge_boot_pages list is ready on pseries. */ #define MAX_NUMBER_GPAGES 1024 __initdata static u64 gpage_freearray[MAX_NUMBER_GPAGES]; __initdata static unsigned nr_gpages; /* * Build list of addresses of gigantic pages. This function is used in early * boot before the buddy allocator is setup. */ void __init pseries_add_gpage(u64 addr, u64 page_size, unsigned long number_of_pages) { if (!addr) return; while (number_of_pages > 0) { gpage_freearray[nr_gpages] = addr; nr_gpages++; number_of_pages--; addr += page_size; } } int __init pseries_alloc_bootmem_huge_page(struct hstate *hstate) { struct huge_bootmem_page *m; if (nr_gpages == 0) return 0; m = phys_to_virt(gpage_freearray[--nr_gpages]); gpage_freearray[nr_gpages] = 0; list_add(&m->list, &huge_boot_pages); m->hstate = hstate; return 1; } #endif int __init alloc_bootmem_huge_page(struct hstate *h) { #ifdef CONFIG_PPC_BOOK3S_64 if (firmware_has_feature(FW_FEATURE_LPAR) && !radix_enabled()) return pseries_alloc_bootmem_huge_page(h); #endif return __alloc_bootmem_huge_page(h); } #if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_8xx) #define HUGEPD_FREELIST_SIZE \ ((PAGE_SIZE - sizeof(struct hugepd_freelist)) / sizeof(pte_t)) struct hugepd_freelist { struct rcu_head rcu; unsigned int index; void *ptes[0]; }; static DEFINE_PER_CPU(struct hugepd_freelist *, hugepd_freelist_cur); static void hugepd_free_rcu_callback(struct rcu_head *head) { struct hugepd_freelist *batch = container_of(head, struct hugepd_freelist, rcu); unsigned int i; for (i = 0; i < batch->index; i++) kmem_cache_free(hugepte_cache, batch->ptes[i]); free_page((unsigned long)batch); } static void hugepd_free(struct mmu_gather *tlb, void *hugepte) { struct hugepd_freelist **batchp; batchp = &get_cpu_var(hugepd_freelist_cur); if (atomic_read(&tlb->mm->mm_users) < 2 || mm_is_thread_local(tlb->mm)) { kmem_cache_free(hugepte_cache, hugepte); put_cpu_var(hugepd_freelist_cur); return; } if (*batchp == NULL) { *batchp = (struct hugepd_freelist *)__get_free_page(GFP_ATOMIC); (*batchp)->index = 0; } (*batchp)->ptes[(*batchp)->index++] = hugepte; if ((*batchp)->index == HUGEPD_FREELIST_SIZE) { call_rcu_sched(&(*batchp)->rcu, hugepd_free_rcu_callback); *batchp = NULL; } put_cpu_var(hugepd_freelist_cur); } #else static inline void hugepd_free(struct mmu_gather *tlb, void *hugepte) {} #endif static void free_hugepd_range(struct mmu_gather *tlb, hugepd_t *hpdp, int pdshift, unsigned long start, unsigned long end, unsigned long floor, unsigned long ceiling) { pte_t *hugepte = hugepd_page(*hpdp); int i; unsigned long pdmask = ~((1UL << pdshift) - 1); unsigned int num_hugepd = 1; unsigned int shift = hugepd_shift(*hpdp); /* Note: On fsl the hpdp may be the first of several */ if (shift > pdshift) num_hugepd = 1 << (shift - pdshift); start &= pdmask; if (start < floor) return; if (ceiling) { ceiling &= pdmask; if (! ceiling) return; } if (end - 1 > ceiling - 1) return; for (i = 0; i < num_hugepd; i++, hpdp++) *hpdp = __hugepd(0); if (shift >= pdshift) hugepd_free(tlb, hugepte); else pgtable_free_tlb(tlb, hugepte, pdshift - shift); } static void hugetlb_free_pmd_range(struct mmu_gather *tlb, pud_t *pud, unsigned long addr, unsigned long end, unsigned long floor, unsigned long ceiling) { pmd_t *pmd; unsigned long next; unsigned long start; start = addr; do { unsigned long more; pmd = pmd_offset(pud, addr); next = pmd_addr_end(addr, end); if (!is_hugepd(__hugepd(pmd_val(*pmd)))) { /* * if it is not hugepd pointer, we should already find * it cleared. */ WARN_ON(!pmd_none_or_clear_bad(pmd)); continue; } /* * Increment next by the size of the huge mapping since * there may be more than one entry at this level for a * single hugepage, but all of them point to * the same kmem cache that holds the hugepte. */ more = addr + (1 << hugepd_shift(*(hugepd_t *)pmd)); if (more > next) next = more; free_hugepd_range(tlb, (hugepd_t *)pmd, PMD_SHIFT, addr, next, floor, ceiling); } while (addr = next, addr != end); start &= PUD_MASK; if (start < floor) return; if (ceiling) { ceiling &= PUD_MASK; if (!ceiling) return; } if (end - 1 > ceiling - 1) return; pmd = pmd_offset(pud, start); pud_clear(pud); pmd_free_tlb(tlb, pmd, start); mm_dec_nr_pmds(tlb->mm); } static void hugetlb_free_pud_range(struct mmu_gather *tlb, pgd_t *pgd, unsigned long addr, unsigned long end, unsigned long floor, unsigned long ceiling) { pud_t *pud; unsigned long next; unsigned long start; start = addr; do { pud = pud_offset(pgd, addr); next = pud_addr_end(addr, end); if (!is_hugepd(__hugepd(pud_val(*pud)))) { if (pud_none_or_clear_bad(pud)) continue; hugetlb_free_pmd_range(tlb, pud, addr, next, floor, ceiling); } else { unsigned long more; /* * Increment next by the size of the huge mapping since * there may be more than one entry at this level for a * single hugepage, but all of them point to * the same kmem cache that holds the hugepte. */ more = addr + (1 << hugepd_shift(*(hugepd_t *)pud)); if (more > next) next = more; free_hugepd_range(tlb, (hugepd_t *)pud, PUD_SHIFT, addr, next, floor, ceiling); } } while (addr = next, addr != end); start &= PGDIR_MASK; if (start < floor) return; if (ceiling) { ceiling &= PGDIR_MASK; if (!ceiling) return; } if (end - 1 > ceiling - 1) return; pud = pud_offset(pgd, start); pgd_clear(pgd); pud_free_tlb(tlb, pud, start); mm_dec_nr_puds(tlb->mm); } /* * This function frees user-level page tables of a process. */ void hugetlb_free_pgd_range(struct mmu_gather *tlb, unsigned long addr, unsigned long end, unsigned long floor, unsigned long ceiling) { pgd_t *pgd; unsigned long next; /* * Because there are a number of different possible pagetable * layouts for hugepage ranges, we limit knowledge of how * things should be laid out to the allocation path * (huge_pte_alloc(), above). Everything else works out the * structure as it goes from information in the hugepd * pointers. That means that we can't here use the * optimization used in the normal page free_pgd_range(), of * checking whether we're actually covering a large enough * range to have to do anything at the top level of the walk * instead of at the bottom. * * To make sense of this, you should probably go read the big * block comment at the top of the normal free_pgd_range(), * too. */ do { next = pgd_addr_end(addr, end); pgd = pgd_offset(tlb->mm, addr); if (!is_hugepd(__hugepd(pgd_val(*pgd)))) { if (pgd_none_or_clear_bad(pgd)) continue; hugetlb_free_pud_range(tlb, pgd, addr, next, floor, ceiling); } else { unsigned long more; /* * Increment next by the size of the huge mapping since * there may be more than one entry at the pgd level * for a single hugepage, but all of them point to the * same kmem cache that holds the hugepte. */ more = addr + (1 << hugepd_shift(*(hugepd_t *)pgd)); if (more > next) next = more; free_hugepd_range(tlb, (hugepd_t *)pgd, PGDIR_SHIFT, addr, next, floor, ceiling); } } while (addr = next, addr != end); } struct page *follow_huge_pd(struct vm_area_struct *vma, unsigned long address, hugepd_t hpd, int flags, int pdshift) { pte_t *ptep; spinlock_t *ptl; struct page *page = NULL; unsigned long mask; int shift = hugepd_shift(hpd); struct mm_struct *mm = vma->vm_mm; retry: ptl = &mm->page_table_lock; spin_lock(ptl); ptep = hugepte_offset(hpd, address, pdshift); if (pte_present(*ptep)) { mask = (1UL << shift) - 1; page = pte_page(*ptep); page += ((address & mask) >> PAGE_SHIFT); if (flags & FOLL_GET) get_page(page); } else { if (is_hugetlb_entry_migration(*ptep)) { spin_unlock(ptl); __migration_entry_wait(mm, ptep, ptl); goto retry; } } spin_unlock(ptl); return page; } static unsigned long hugepte_addr_end(unsigned long addr, unsigned long end, unsigned long sz) { unsigned long __boundary = (addr + sz) & ~(sz-1); return (__boundary - 1 < end - 1) ? __boundary : end; } int gup_huge_pd(hugepd_t hugepd, unsigned long addr, unsigned pdshift, unsigned long end, int write, struct page **pages, int *nr) { pte_t *ptep; unsigned long sz = 1UL << hugepd_shift(hugepd); unsigned long next; ptep = hugepte_offset(hugepd, addr, pdshift); do { next = hugepte_addr_end(addr, end, sz); if (!gup_hugepte(ptep, sz, addr, end, write, pages, nr)) return 0; } while (ptep++, addr = next, addr != end); return 1; } #ifdef CONFIG_PPC_MM_SLICES unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr, unsigned long len, unsigned long pgoff, unsigned long flags) { struct hstate *hstate = hstate_file(file); int mmu_psize = shift_to_mmu_psize(huge_page_shift(hstate)); if (radix_enabled()) return radix__hugetlb_get_unmapped_area(file, addr, len, pgoff, flags); return slice_get_unmapped_area(addr, len, flags, mmu_psize, 1); } #endif unsigned long vma_mmu_pagesize(struct vm_area_struct *vma) { #ifdef CONFIG_PPC_MM_SLICES unsigned int psize = get_slice_psize(vma->vm_mm, vma->vm_start); /* With radix we don't use slice, so derive it from vma*/ if (!radix_enabled()) return 1UL << mmu_psize_to_shift(psize); #endif if (!is_vm_hugetlb_page(vma)) return PAGE_SIZE; return huge_page_size(hstate_vma(vma)); } static inline bool is_power_of_4(unsigned long x) { if (is_power_of_2(x)) return (__ilog2(x) % 2) ? false : true; return false; } static int __init add_huge_page_size(unsigned long long size) { int shift = __ffs(size); int mmu_psize; /* Check that it is a page size supported by the hardware and * that it fits within pagetable and slice limits. */ if (size <= PAGE_SIZE) return -EINVAL; #if defined(CONFIG_PPC_FSL_BOOK3E) if (!is_power_of_4(size)) return -EINVAL; #elif !defined(CONFIG_PPC_8xx) if (!is_power_of_2(size) || (shift > SLICE_HIGH_SHIFT)) return -EINVAL; #endif if ((mmu_psize = shift_to_mmu_psize(shift)) < 0) return -EINVAL; #ifdef CONFIG_PPC_BOOK3S_64 /* * We need to make sure that for different page sizes reported by * firmware we only add hugetlb support for page sizes that can be * supported by linux page table layout. * For now we have * Radix: 2M * Hash: 16M and 16G */ if (radix_enabled()) { if (mmu_psize != MMU_PAGE_2M) { if (cpu_has_feature(CPU_FTR_POWER9_DD1) || (mmu_psize != MMU_PAGE_1G)) return -EINVAL; } } else { if (mmu_psize != MMU_PAGE_16M && mmu_psize != MMU_PAGE_16G) return -EINVAL; } #endif BUG_ON(mmu_psize_defs[mmu_psize].shift != shift); /* Return if huge page size has already been setup */ if (size_to_hstate(size)) return 0; hugetlb_add_hstate(shift - PAGE_SHIFT); return 0; } static int __init hugepage_setup_sz(char *str) { unsigned long long size; size = memparse(str, &str); if (add_huge_page_size(size) != 0) { hugetlb_bad_size(); pr_err("Invalid huge page size specified(%llu)\n", size); } return 1; } __setup("hugepagesz=", hugepage_setup_sz); struct kmem_cache *hugepte_cache; static int __init hugetlbpage_init(void) { int psize; #if !defined(CONFIG_PPC_FSL_BOOK3E) && !defined(CONFIG_PPC_8xx) if (!radix_enabled() && !mmu_has_feature(MMU_FTR_16M_PAGE)) return -ENODEV; #endif for (psize = 0; psize < MMU_PAGE_COUNT; ++psize) { unsigned shift; unsigned pdshift; if (!mmu_psize_defs[psize].shift) continue; shift = mmu_psize_to_shift(psize); if (add_huge_page_size(1ULL << shift) < 0) continue; if (shift < HUGEPD_PUD_SHIFT) pdshift = PMD_SHIFT; else if (shift < HUGEPD_PGD_SHIFT) pdshift = PUD_SHIFT; else pdshift = PGDIR_SHIFT; /* * if we have pdshift and shift value same, we don't * use pgt cache for hugepd. */ if (pdshift > shift) pgtable_cache_add(pdshift - shift, NULL); #if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_8xx) else if (!hugepte_cache) { /* * Create a kmem cache for hugeptes. The bottom bits in * the pte have size information encoded in them, so * align them to allow this */ hugepte_cache = kmem_cache_create("hugepte-cache", sizeof(pte_t), HUGEPD_SHIFT_MASK + 1, 0, NULL); if (hugepte_cache == NULL) panic("%s: Unable to create kmem cache " "for hugeptes\n", __func__); } #endif } #if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_8xx) /* Default hpage size = 4M on FSL_BOOK3E and 512k on 8xx */ if (mmu_psize_defs[MMU_PAGE_4M].shift) HPAGE_SHIFT = mmu_psize_defs[MMU_PAGE_4M].shift; else if (mmu_psize_defs[MMU_PAGE_512K].shift) HPAGE_SHIFT = mmu_psize_defs[MMU_PAGE_512K].shift; #else /* Set default large page size. Currently, we pick 16M or 1M * depending on what is available */ if (mmu_psize_defs[MMU_PAGE_16M].shift) HPAGE_SHIFT = mmu_psize_defs[MMU_PAGE_16M].shift; else if (mmu_psize_defs[MMU_PAGE_1M].shift) HPAGE_SHIFT = mmu_psize_defs[MMU_PAGE_1M].shift; else if (mmu_psize_defs[MMU_PAGE_2M].shift) HPAGE_SHIFT = mmu_psize_defs[MMU_PAGE_2M].shift; #endif return 0; } arch_initcall(hugetlbpage_init); void flush_dcache_icache_hugepage(struct page *page) { int i; void *start; BUG_ON(!PageCompound(page)); for (i = 0; i < (1UL << compound_order(page)); i++) { if (!PageHighMem(page)) { __flush_dcache_icache(page_address(page+i)); } else { start = kmap_atomic(page+i); __flush_dcache_icache(start); kunmap_atomic(start); } } } #endif /* CONFIG_HUGETLB_PAGE */ /* * We have 4 cases for pgds and pmds: * (1) invalid (all zeroes) * (2) pointer to next table, as normal; bottom 6 bits == 0 * (3) leaf pte for huge page _PAGE_PTE set * (4) hugepd pointer, _PAGE_PTE = 0 and bits [2..6] indicate size of table * * So long as we atomically load page table pointers we are safe against teardown, * we can follow the address down to the the page and take a ref on it. * This function need to be called with interrupts disabled. We use this variant * when we have MSR[EE] = 0 but the paca->soft_enabled = IRQS_ENABLED */ pte_t *__find_linux_pte(pgd_t *pgdir, unsigned long ea, bool *is_thp, unsigned *hpage_shift) { pgd_t pgd, *pgdp; pud_t pud, *pudp; pmd_t pmd, *pmdp; pte_t *ret_pte; hugepd_t *hpdp = NULL; unsigned pdshift = PGDIR_SHIFT; if (hpage_shift) *hpage_shift = 0; if (is_thp) *is_thp = false; pgdp = pgdir + pgd_index(ea); pgd = READ_ONCE(*pgdp); /* * Always operate on the local stack value. This make sure the * value don't get updated by a parallel THP split/collapse, * page fault or a page unmap. The return pte_t * is still not * stable. So should be checked there for above conditions. */ if (pgd_none(pgd)) return NULL; else if (pgd_huge(pgd)) { ret_pte = (pte_t *) pgdp; goto out; } else if (is_hugepd(__hugepd(pgd_val(pgd)))) hpdp = (hugepd_t *)&pgd; else { /* * Even if we end up with an unmap, the pgtable will not * be freed, because we do an rcu free and here we are * irq disabled */ pdshift = PUD_SHIFT; pudp = pud_offset(&pgd, ea); pud = READ_ONCE(*pudp); if (pud_none(pud)) return NULL; else if (pud_huge(pud)) { ret_pte = (pte_t *) pudp; goto out; } else if (is_hugepd(__hugepd(pud_val(pud)))) hpdp = (hugepd_t *)&pud; else { pdshift = PMD_SHIFT; pmdp = pmd_offset(&pud, ea); pmd = READ_ONCE(*pmdp); /* * A hugepage collapse is captured by pmd_none, because * it mark the pmd none and do a hpte invalidate. */ if (pmd_none(pmd)) return NULL; if (pmd_trans_huge(pmd) || pmd_devmap(pmd)) { if (is_thp) *is_thp = true; ret_pte = (pte_t *) pmdp; goto out; } if (pmd_huge(pmd)) { ret_pte = (pte_t *) pmdp; goto out; } else if (is_hugepd(__hugepd(pmd_val(pmd)))) hpdp = (hugepd_t *)&pmd; else return pte_offset_kernel(&pmd, ea); } } if (!hpdp) return NULL; ret_pte = hugepte_offset(*hpdp, ea, pdshift); pdshift = hugepd_shift(*hpdp); out: if (hpage_shift) *hpage_shift = pdshift; return ret_pte; } EXPORT_SYMBOL_GPL(__find_linux_pte); int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr, unsigned long end, int write, struct page **pages, int *nr) { unsigned long pte_end; struct page *head, *page; pte_t pte; int refs; pte_end = (addr + sz) & ~(sz-1); if (pte_end < end) end = pte_end; pte = READ_ONCE(*ptep); if (!pte_access_permitted(pte, write)) return 0; /* hugepages are never "special" */ VM_BUG_ON(!pfn_valid(pte_pfn(pte))); refs = 0; head = pte_page(pte); page = head + ((addr & (sz-1)) >> PAGE_SHIFT); do { VM_BUG_ON(compound_head(page) != head); pages[*nr] = page; (*nr)++; page++; refs++; } while (addr += PAGE_SIZE, addr != end); if (!page_cache_add_speculative(head, refs)) { *nr -= refs; return 0; } if (unlikely(pte_val(pte) != pte_val(*ptep))) { /* Could be optimized better */ *nr -= refs; while (refs--) put_page(head); return 0; } return 1; }