/* * mm/rmap.c - physical to virtual reverse mappings * * Copyright 2001, Rik van Riel <riel@conectiva.com.br> * Released under the General Public License (GPL). * * Simple, low overhead reverse mapping scheme. * Please try to keep this thing as modular as possible. * * Provides methods for unmapping each kind of mapped page: * the anon methods track anonymous pages, and * the file methods track pages belonging to an inode. * * Original design by Rik van Riel <riel@conectiva.com.br> 2001 * File methods by Dave McCracken <dmccr@us.ibm.com> 2003, 2004 * Anonymous methods by Andrea Arcangeli <andrea@suse.de> 2004 * Contributions by Hugh Dickins 2003, 2004 */ /* * Lock ordering in mm: * * inode->i_mutex (while writing or truncating, not reading or faulting) * inode->i_alloc_sem (vmtruncate_range) * mm->mmap_sem * page->flags PG_locked (lock_page) * mapping->i_mmap_mutex * anon_vma->lock * mm->page_table_lock or pte_lock * zone->lru_lock (in mark_page_accessed, isolate_lru_page) * swap_lock (in swap_duplicate, swap_info_get) * mmlist_lock (in mmput, drain_mmlist and others) * mapping->private_lock (in __set_page_dirty_buffers) * inode->i_lock (in set_page_dirty's __mark_inode_dirty) * inode_wb_list_lock (in set_page_dirty's __mark_inode_dirty) * sb_lock (within inode_lock in fs/fs-writeback.c) * mapping->tree_lock (widely used, in set_page_dirty, * in arch-dependent flush_dcache_mmap_lock, * within inode_wb_list_lock in __sync_single_inode) * * (code doesn't rely on that order so it could be switched around) * ->tasklist_lock * anon_vma->lock (memory_failure, collect_procs_anon) * pte map lock */ #include <linux/mm.h> #include <linux/pagemap.h> #include <linux/swap.h> #include <linux/swapops.h> #include <linux/slab.h> #include <linux/init.h> #include <linux/ksm.h> #include <linux/rmap.h> #include <linux/rcupdate.h> #include <linux/module.h> #include <linux/memcontrol.h> #include <linux/mmu_notifier.h> #include <linux/migrate.h> #include <linux/hugetlb.h> #include <asm/tlbflush.h> #include "internal.h" static struct kmem_cache *anon_vma_cachep; static struct kmem_cache *anon_vma_chain_cachep; static inline struct anon_vma *anon_vma_alloc(void) { struct anon_vma *anon_vma; anon_vma = kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL); if (anon_vma) { atomic_set(&anon_vma->refcount, 1); /* * Initialise the anon_vma root to point to itself. If called * from fork, the root will be reset to the parents anon_vma. */ anon_vma->root = anon_vma; } return anon_vma; } static inline void anon_vma_free(struct anon_vma *anon_vma) { VM_BUG_ON(atomic_read(&anon_vma->refcount)); kmem_cache_free(anon_vma_cachep, anon_vma); } static inline struct anon_vma_chain *anon_vma_chain_alloc(void) { return kmem_cache_alloc(anon_vma_chain_cachep, GFP_KERNEL); } static void anon_vma_chain_free(struct anon_vma_chain *anon_vma_chain) { kmem_cache_free(anon_vma_chain_cachep, anon_vma_chain); } /** * anon_vma_prepare - attach an anon_vma to a memory region * @vma: the memory region in question * * This makes sure the memory mapping described by 'vma' has * an 'anon_vma' attached to it, so that we can associate the * anonymous pages mapped into it with that anon_vma. * * The common case will be that we already have one, but if * not we either need to find an adjacent mapping that we * can re-use the anon_vma from (very common when the only * reason for splitting a vma has been mprotect()), or we * allocate a new one. * * Anon-vma allocations are very subtle, because we may have * optimistically looked up an anon_vma in page_lock_anon_vma() * and that may actually touch the spinlock even in the newly * allocated vma (it depends on RCU to make sure that the * anon_vma isn't actually destroyed). * * As a result, we need to do proper anon_vma locking even * for the new allocation. At the same time, we do not want * to do any locking for the common case of already having * an anon_vma. * * This must be called with the mmap_sem held for reading. */ int anon_vma_prepare(struct vm_area_struct *vma) { struct anon_vma *anon_vma = vma->anon_vma; struct anon_vma_chain *avc; might_sleep(); if (unlikely(!anon_vma)) { struct mm_struct *mm = vma->vm_mm; struct anon_vma *allocated; avc = anon_vma_chain_alloc(); if (!avc) goto out_enomem; anon_vma = find_mergeable_anon_vma(vma); allocated = NULL; if (!anon_vma) { anon_vma = anon_vma_alloc(); if (unlikely(!anon_vma)) goto out_enomem_free_avc; allocated = anon_vma; } anon_vma_lock(anon_vma); /* page_table_lock to protect against threads */ spin_lock(&mm->page_table_lock); if (likely(!vma->anon_vma)) { vma->anon_vma = anon_vma; avc->anon_vma = anon_vma; avc->vma = vma; list_add(&avc->same_vma, &vma->anon_vma_chain); list_add_tail(&avc->same_anon_vma, &anon_vma->head); allocated = NULL; avc = NULL; } spin_unlock(&mm->page_table_lock); anon_vma_unlock(anon_vma); if (unlikely(allocated)) put_anon_vma(allocated); if (unlikely(avc)) anon_vma_chain_free(avc); } return 0; out_enomem_free_avc: anon_vma_chain_free(avc); out_enomem: return -ENOMEM; } static void anon_vma_chain_link(struct vm_area_struct *vma, struct anon_vma_chain *avc, struct anon_vma *anon_vma) { avc->vma = vma; avc->anon_vma = anon_vma; list_add(&avc->same_vma, &vma->anon_vma_chain); anon_vma_lock(anon_vma); /* * It's critical to add new vmas to the tail of the anon_vma, * see comment in huge_memory.c:__split_huge_page(). */ list_add_tail(&avc->same_anon_vma, &anon_vma->head); anon_vma_unlock(anon_vma); } /* * Attach the anon_vmas from src to dst. * Returns 0 on success, -ENOMEM on failure. */ int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src) { struct anon_vma_chain *avc, *pavc; list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) { avc = anon_vma_chain_alloc(); if (!avc) goto enomem_failure; anon_vma_chain_link(dst, avc, pavc->anon_vma); } return 0; enomem_failure: unlink_anon_vmas(dst); return -ENOMEM; } /* * Attach vma to its own anon_vma, as well as to the anon_vmas that * the corresponding VMA in the parent process is attached to. * Returns 0 on success, non-zero on failure. */ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma) { struct anon_vma_chain *avc; struct anon_vma *anon_vma; /* Don't bother if the parent process has no anon_vma here. */ if (!pvma->anon_vma) return 0; /* * First, attach the new VMA to the parent VMA's anon_vmas, * so rmap can find non-COWed pages in child processes. */ if (anon_vma_clone(vma, pvma)) return -ENOMEM; /* Then add our own anon_vma. */ anon_vma = anon_vma_alloc(); if (!anon_vma) goto out_error; avc = anon_vma_chain_alloc(); if (!avc) goto out_error_free_anon_vma; /* * The root anon_vma's spinlock is the lock actually used when we * lock any of the anon_vmas in this anon_vma tree. */ anon_vma->root = pvma->anon_vma->root; /* * With refcounts, an anon_vma can stay around longer than the * process it belongs to. The root anon_vma needs to be pinned until * this anon_vma is freed, because the lock lives in the root. */ get_anon_vma(anon_vma->root); /* Mark this anon_vma as the one where our new (COWed) pages go. */ vma->anon_vma = anon_vma; anon_vma_chain_link(vma, avc, anon_vma); return 0; out_error_free_anon_vma: put_anon_vma(anon_vma); out_error: unlink_anon_vmas(vma); return -ENOMEM; } static void anon_vma_unlink(struct anon_vma_chain *anon_vma_chain) { struct anon_vma *anon_vma = anon_vma_chain->anon_vma; int empty; /* If anon_vma_fork fails, we can get an empty anon_vma_chain. */ if (!anon_vma) return; anon_vma_lock(anon_vma); list_del(&anon_vma_chain->same_anon_vma); /* We must garbage collect the anon_vma if it's empty */ empty = list_empty(&anon_vma->head); anon_vma_unlock(anon_vma); if (empty) put_anon_vma(anon_vma); } void unlink_anon_vmas(struct vm_area_struct *vma) { struct anon_vma_chain *avc, *next; /* * Unlink each anon_vma chained to the VMA. This list is ordered * from newest to oldest, ensuring the root anon_vma gets freed last. */ list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) { anon_vma_unlink(avc); list_del(&avc->same_vma); anon_vma_chain_free(avc); } } static void anon_vma_ctor(void *data) { struct anon_vma *anon_vma = data; spin_lock_init(&anon_vma->lock); atomic_set(&anon_vma->refcount, 0); INIT_LIST_HEAD(&anon_vma->head); } void __init anon_vma_init(void) { anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma), 0, SLAB_DESTROY_BY_RCU|SLAB_PANIC, anon_vma_ctor); anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain, SLAB_PANIC); } /* * Getting a lock on a stable anon_vma from a page off the LRU is * tricky: page_lock_anon_vma rely on RCU to guard against the races. */ struct anon_vma *__page_lock_anon_vma(struct page *page) { struct anon_vma *anon_vma, *root_anon_vma; unsigned long anon_mapping; rcu_read_lock(); anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping); if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON) goto out; if (!page_mapped(page)) goto out; anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON); root_anon_vma = ACCESS_ONCE(anon_vma->root); spin_lock(&root_anon_vma->lock); /* * If this page is still mapped, then its anon_vma cannot have been * freed. But if it has been unmapped, we have no security against * the anon_vma structure being freed and reused (for another anon_vma: * SLAB_DESTROY_BY_RCU guarantees that - so the spin_lock above cannot * corrupt): with anon_vma_prepare() or anon_vma_fork() redirecting * anon_vma->root before page_unlock_anon_vma() is called to unlock. */ if (page_mapped(page)) return anon_vma; spin_unlock(&root_anon_vma->lock); out: rcu_read_unlock(); return NULL; } void page_unlock_anon_vma(struct anon_vma *anon_vma) __releases(&anon_vma->root->lock) __releases(RCU) { anon_vma_unlock(anon_vma); rcu_read_unlock(); } /* * At what user virtual address is page expected in @vma? * Returns virtual address or -EFAULT if page's index/offset is not * within the range mapped the @vma. */ inline unsigned long vma_address(struct page *page, struct vm_area_struct *vma) { pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); unsigned long address; if (unlikely(is_vm_hugetlb_page(vma))) pgoff = page->index << huge_page_order(page_hstate(page)); address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT); if (unlikely(address < vma->vm_start || address >= vma->vm_end)) { /* page should be within @vma mapping range */ return -EFAULT; } return address; } /* * At what user virtual address is page expected in vma? * Caller should check the page is actually part of the vma. */ unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma) { if (PageAnon(page)) { struct anon_vma *page__anon_vma = page_anon_vma(page); /* * Note: swapoff's unuse_vma() is more efficient with this * check, and needs it to match anon_vma when KSM is active. */ if (!vma->anon_vma || !page__anon_vma || vma->anon_vma->root != page__anon_vma->root) return -EFAULT; } else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) { if (!vma->vm_file || vma->vm_file->f_mapping != page->mapping) return -EFAULT; } else return -EFAULT; return vma_address(page, vma); } /* * Check that @page is mapped at @address into @mm. * * If @sync is false, page_check_address may perform a racy check to avoid * the page table lock when the pte is not present (helpful when reclaiming * highly shared pages). * * On success returns with pte mapped and locked. */ pte_t *__page_check_address(struct page *page, struct mm_struct *mm, unsigned long address, spinlock_t **ptlp, int sync) { pgd_t *pgd; pud_t *pud; pmd_t *pmd; pte_t *pte; spinlock_t *ptl; if (unlikely(PageHuge(page))) { pte = huge_pte_offset(mm, address); ptl = &mm->page_table_lock; goto check; } pgd = pgd_offset(mm, address); if (!pgd_present(*pgd)) return NULL; pud = pud_offset(pgd, address); if (!pud_present(*pud)) return NULL; pmd = pmd_offset(pud, address); if (!pmd_present(*pmd)) return NULL; if (pmd_trans_huge(*pmd)) return NULL; pte = pte_offset_map(pmd, address); /* Make a quick check before getting the lock */ if (!sync && !pte_present(*pte)) { pte_unmap(pte); return NULL; } ptl = pte_lockptr(mm, pmd); check: spin_lock(ptl); if (pte_present(*pte) && page_to_pfn(page) == pte_pfn(*pte)) { *ptlp = ptl; return pte; } pte_unmap_unlock(pte, ptl); return NULL; } /** * page_mapped_in_vma - check whether a page is really mapped in a VMA * @page: the page to test * @vma: the VMA to test * * Returns 1 if the page is mapped into the page tables of the VMA, 0 * if the page is not mapped into the page tables of this VMA. Only * valid for normal file or anonymous VMAs. */ int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma) { unsigned long address; pte_t *pte; spinlock_t *ptl; address = vma_address(page, vma); if (address == -EFAULT) /* out of vma range */ return 0; pte = page_check_address(page, vma->vm_mm, address, &ptl, 1); if (!pte) /* the page is not in this mm */ return 0; pte_unmap_unlock(pte, ptl); return 1; } /* * Subfunctions of page_referenced: page_referenced_one called * repeatedly from either page_referenced_anon or page_referenced_file. */ int page_referenced_one(struct page *page, struct vm_area_struct *vma, unsigned long address, unsigned int *mapcount, unsigned long *vm_flags) { struct mm_struct *mm = vma->vm_mm; int referenced = 0; if (unlikely(PageTransHuge(page))) { pmd_t *pmd; spin_lock(&mm->page_table_lock); /* * rmap might return false positives; we must filter * these out using page_check_address_pmd(). */ pmd = page_check_address_pmd(page, mm, address, PAGE_CHECK_ADDRESS_PMD_FLAG); if (!pmd) { spin_unlock(&mm->page_table_lock); goto out; } if (vma->vm_flags & VM_LOCKED) { spin_unlock(&mm->page_table_lock); *mapcount = 0; /* break early from loop */ *vm_flags |= VM_LOCKED; goto out; } /* go ahead even if the pmd is pmd_trans_splitting() */ if (pmdp_clear_flush_young_notify(vma, address, pmd)) referenced++; spin_unlock(&mm->page_table_lock); } else { pte_t *pte; spinlock_t *ptl; /* * rmap might return false positives; we must filter * these out using page_check_address(). */ pte = page_check_address(page, mm, address, &ptl, 0); if (!pte) goto out; if (vma->vm_flags & VM_LOCKED) { pte_unmap_unlock(pte, ptl); *mapcount = 0; /* break early from loop */ *vm_flags |= VM_LOCKED; goto out; } if (ptep_clear_flush_young_notify(vma, address, pte)) { /* * Don't treat a reference through a sequentially read * mapping as such. If the page has been used in * another mapping, we will catch it; if this other * mapping is already gone, the unmap path will have * set PG_referenced or activated the page. */ if (likely(!VM_SequentialReadHint(vma))) referenced++; } pte_unmap_unlock(pte, ptl); } /* Pretend the page is referenced if the task has the swap token and is in the middle of a page fault. */ if (mm != current->mm && has_swap_token(mm) && rwsem_is_locked(&mm->mmap_sem)) referenced++; (*mapcount)--; if (referenced) *vm_flags |= vma->vm_flags; out: return referenced; } static int page_referenced_anon(struct page *page, struct mem_cgroup *mem_cont, unsigned long *vm_flags) { unsigned int mapcount; struct anon_vma *anon_vma; struct anon_vma_chain *avc; int referenced = 0; anon_vma = page_lock_anon_vma(page); if (!anon_vma) return referenced; mapcount = page_mapcount(page); list_for_each_entry(avc, &anon_vma->head, same_anon_vma) { struct vm_area_struct *vma = avc->vma; unsigned long address = vma_address(page, vma); if (address == -EFAULT) continue; /* * If we are reclaiming on behalf of a cgroup, skip * counting on behalf of references from different * cgroups */ if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont)) continue; referenced += page_referenced_one(page, vma, address, &mapcount, vm_flags); if (!mapcount) break; } page_unlock_anon_vma(anon_vma); return referenced; } /** * page_referenced_file - referenced check for object-based rmap * @page: the page we're checking references on. * @mem_cont: target memory controller * @vm_flags: collect encountered vma->vm_flags who actually referenced the page * * For an object-based mapped page, find all the places it is mapped and * check/clear the referenced flag. This is done by following the page->mapping * pointer, then walking the chain of vmas it holds. It returns the number * of references it found. * * This function is only called from page_referenced for object-based pages. */ static int page_referenced_file(struct page *page, struct mem_cgroup *mem_cont, unsigned long *vm_flags) { unsigned int mapcount; struct address_space *mapping = page->mapping; pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); struct vm_area_struct *vma; struct prio_tree_iter iter; int referenced = 0; /* * The caller's checks on page->mapping and !PageAnon have made * sure that this is a file page: the check for page->mapping * excludes the case just before it gets set on an anon page. */ BUG_ON(PageAnon(page)); /* * The page lock not only makes sure that page->mapping cannot * suddenly be NULLified by truncation, it makes sure that the * structure at mapping cannot be freed and reused yet, * so we can safely take mapping->i_mmap_mutex. */ BUG_ON(!PageLocked(page)); mutex_lock(&mapping->i_mmap_mutex); /* * i_mmap_mutex does not stabilize mapcount at all, but mapcount * is more likely to be accurate if we note it after spinning. */ mapcount = page_mapcount(page); vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) { unsigned long address = vma_address(page, vma); if (address == -EFAULT) continue; /* * If we are reclaiming on behalf of a cgroup, skip * counting on behalf of references from different * cgroups */ if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont)) continue; referenced += page_referenced_one(page, vma, address, &mapcount, vm_flags); if (!mapcount) break; } mutex_unlock(&mapping->i_mmap_mutex); return referenced; } /** * page_referenced - test if the page was referenced * @page: the page to test * @is_locked: caller holds lock on the page * @mem_cont: target memory controller * @vm_flags: collect encountered vma->vm_flags who actually referenced the page * * Quick test_and_clear_referenced for all mappings to a page, * returns the number of ptes which referenced the page. */ int page_referenced(struct page *page, int is_locked, struct mem_cgroup *mem_cont, unsigned long *vm_flags) { int referenced = 0; int we_locked = 0; *vm_flags = 0; if (page_mapped(page) && page_rmapping(page)) { if (!is_locked && (!PageAnon(page) || PageKsm(page))) { we_locked = trylock_page(page); if (!we_locked) { referenced++; goto out; } } if (unlikely(PageKsm(page))) referenced += page_referenced_ksm(page, mem_cont, vm_flags); else if (PageAnon(page)) referenced += page_referenced_anon(page, mem_cont, vm_flags); else if (page->mapping) referenced += page_referenced_file(page, mem_cont, vm_flags); if (we_locked) unlock_page(page); } out: if (page_test_and_clear_young(page_to_pfn(page))) referenced++; return referenced; } static int page_mkclean_one(struct page *page, struct vm_area_struct *vma, unsigned long address) { struct mm_struct *mm = vma->vm_mm; pte_t *pte; spinlock_t *ptl; int ret = 0; pte = page_check_address(page, mm, address, &ptl, 1); if (!pte) goto out; if (pte_dirty(*pte) || pte_write(*pte)) { pte_t entry; flush_cache_page(vma, address, pte_pfn(*pte)); entry = ptep_clear_flush_notify(vma, address, pte); entry = pte_wrprotect(entry); entry = pte_mkclean(entry); set_pte_at(mm, address, pte, entry); ret = 1; } pte_unmap_unlock(pte, ptl); out: return ret; } static int page_mkclean_file(struct address_space *mapping, struct page *page) { pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); struct vm_area_struct *vma; struct prio_tree_iter iter; int ret = 0; BUG_ON(PageAnon(page)); mutex_lock(&mapping->i_mmap_mutex); vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) { if (vma->vm_flags & VM_SHARED) { unsigned long address = vma_address(page, vma); if (address == -EFAULT) continue; ret += page_mkclean_one(page, vma, address); } } mutex_unlock(&mapping->i_mmap_mutex); return ret; } int page_mkclean(struct page *page) { int ret = 0; BUG_ON(!PageLocked(page)); if (page_mapped(page)) { struct address_space *mapping = page_mapping(page); if (mapping) { ret = page_mkclean_file(mapping, page); if (page_test_and_clear_dirty(page_to_pfn(page), 1)) ret = 1; } } return ret; } EXPORT_SYMBOL_GPL(page_mkclean); /** * page_move_anon_rmap - move a page to our anon_vma * @page: the page to move to our anon_vma * @vma: the vma the page belongs to * @address: the user virtual address mapped * * When a page belongs exclusively to one process after a COW event, * that page can be moved into the anon_vma that belongs to just that * process, so the rmap code will not search the parent or sibling * processes. */ void page_move_anon_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address) { struct anon_vma *anon_vma = vma->anon_vma; VM_BUG_ON(!PageLocked(page)); VM_BUG_ON(!anon_vma); VM_BUG_ON(page->index != linear_page_index(vma, address)); anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON; page->mapping = (struct address_space *) anon_vma; } /** * __page_set_anon_rmap - set up new anonymous rmap * @page: Page to add to rmap * @vma: VM area to add page to. * @address: User virtual address of the mapping * @exclusive: the page is exclusively owned by the current process */ static void __page_set_anon_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address, int exclusive) { struct anon_vma *anon_vma = vma->anon_vma; BUG_ON(!anon_vma); if (PageAnon(page)) return; /* * If the page isn't exclusively mapped into this vma, * we must use the _oldest_ possible anon_vma for the * page mapping! */ if (!exclusive) anon_vma = anon_vma->root; anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON; page->mapping = (struct address_space *) anon_vma; page->index = linear_page_index(vma, address); } /** * __page_check_anon_rmap - sanity check anonymous rmap addition * @page: the page to add the mapping to * @vma: the vm area in which the mapping is added * @address: the user virtual address mapped */ static void __page_check_anon_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address) { #ifdef CONFIG_DEBUG_VM /* * The page's anon-rmap details (mapping and index) are guaranteed to * be set up correctly at this point. * * We have exclusion against page_add_anon_rmap because the caller * always holds the page locked, except if called from page_dup_rmap, * in which case the page is already known to be setup. * * We have exclusion against page_add_new_anon_rmap because those pages * are initially only visible via the pagetables, and the pte is locked * over the call to page_add_new_anon_rmap. */ BUG_ON(page_anon_vma(page)->root != vma->anon_vma->root); BUG_ON(page->index != linear_page_index(vma, address)); #endif } /** * page_add_anon_rmap - add pte mapping to an anonymous page * @page: the page to add the mapping to * @vma: the vm area in which the mapping is added * @address: the user virtual address mapped * * The caller needs to hold the pte lock, and the page must be locked in * the anon_vma case: to serialize mapping,index checking after setting, * and to ensure that PageAnon is not being upgraded racily to PageKsm * (but PageKsm is never downgraded to PageAnon). */ void page_add_anon_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address) { do_page_add_anon_rmap(page, vma, address, 0); } /* * Special version of the above for do_swap_page, which often runs * into pages that are exclusively owned by the current process. * Everybody else should continue to use page_add_anon_rmap above. */ void do_page_add_anon_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address, int exclusive) { int first = atomic_inc_and_test(&page->_mapcount); if (first) { if (!PageTransHuge(page)) __inc_zone_page_state(page, NR_ANON_PAGES); else __inc_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES); } if (unlikely(PageKsm(page))) return; VM_BUG_ON(!PageLocked(page)); VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end); if (first) __page_set_anon_rmap(page, vma, address, exclusive); else __page_check_anon_rmap(page, vma, address); } /** * page_add_new_anon_rmap - add pte mapping to a new anonymous page * @page: the page to add the mapping to * @vma: the vm area in which the mapping is added * @address: the user virtual address mapped * * Same as page_add_anon_rmap but must only be called on *new* pages. * This means the inc-and-test can be bypassed. * Page does not have to be locked. */ void page_add_new_anon_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address) { VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end); SetPageSwapBacked(page); atomic_set(&page->_mapcount, 0); /* increment count (starts at -1) */ if (!PageTransHuge(page)) __inc_zone_page_state(page, NR_ANON_PAGES); else __inc_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES); __page_set_anon_rmap(page, vma, address, 1); if (page_evictable(page, vma)) lru_cache_add_lru(page, LRU_ACTIVE_ANON); else add_page_to_unevictable_list(page); } /** * page_add_file_rmap - add pte mapping to a file page * @page: the page to add the mapping to * * The caller needs to hold the pte lock. */ void page_add_file_rmap(struct page *page) { if (atomic_inc_and_test(&page->_mapcount)) { __inc_zone_page_state(page, NR_FILE_MAPPED); mem_cgroup_inc_page_stat(page, MEMCG_NR_FILE_MAPPED); } } /** * page_remove_rmap - take down pte mapping from a page * @page: page to remove mapping from * * The caller needs to hold the pte lock. */ void page_remove_rmap(struct page *page) { /* page still mapped by someone else? */ if (!atomic_add_negative(-1, &page->_mapcount)) return; /* * Now that the last pte has gone, s390 must transfer dirty * flag from storage key to struct page. We can usually skip * this if the page is anon, so about to be freed; but perhaps * not if it's in swapcache - there might be another pte slot * containing the swap entry, but page not yet written to swap. */ if ((!PageAnon(page) || PageSwapCache(page)) && page_test_and_clear_dirty(page_to_pfn(page), 1)) set_page_dirty(page); /* * Hugepages are not counted in NR_ANON_PAGES nor NR_FILE_MAPPED * and not charged by memcg for now. */ if (unlikely(PageHuge(page))) return; if (PageAnon(page)) { mem_cgroup_uncharge_page(page); if (!PageTransHuge(page)) __dec_zone_page_state(page, NR_ANON_PAGES); else __dec_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES); } else { __dec_zone_page_state(page, NR_FILE_MAPPED); mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_MAPPED); } /* * It would be tidy to reset the PageAnon mapping here, * but that might overwrite a racing page_add_anon_rmap * which increments mapcount after us but sets mapping * before us: so leave the reset to free_hot_cold_page, * and remember that it's only reliable while mapped. * Leaving it set also helps swapoff to reinstate ptes * faster for those pages still in swapcache. */ } /* * Subfunctions of try_to_unmap: try_to_unmap_one called * repeatedly from either try_to_unmap_anon or try_to_unmap_file. */ int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, unsigned long address, enum ttu_flags flags) { struct mm_struct *mm = vma->vm_mm; pte_t *pte; pte_t pteval; spinlock_t *ptl; int ret = SWAP_AGAIN; pte = page_check_address(page, mm, address, &ptl, 0); if (!pte) goto out; /* * If the page is mlock()d, we cannot swap it out. * If it's recently referenced (perhaps page_referenced * skipped over this mm) then we should reactivate it. */ if (!(flags & TTU_IGNORE_MLOCK)) { if (vma->vm_flags & VM_LOCKED) goto out_mlock; if (TTU_ACTION(flags) == TTU_MUNLOCK) goto out_unmap; } if (!(flags & TTU_IGNORE_ACCESS)) { if (ptep_clear_flush_young_notify(vma, address, pte)) { ret = SWAP_FAIL; goto out_unmap; } } /* Nuke the page table entry. */ flush_cache_page(vma, address, page_to_pfn(page)); pteval = ptep_clear_flush_notify(vma, address, pte); /* Move the dirty bit to the physical page now the pte is gone. */ if (pte_dirty(pteval)) set_page_dirty(page); /* Update high watermark before we lower rss */ update_hiwater_rss(mm); if (PageHWPoison(page) && !(flags & TTU_IGNORE_HWPOISON)) { if (PageAnon(page)) dec_mm_counter(mm, MM_ANONPAGES); else dec_mm_counter(mm, MM_FILEPAGES); set_pte_at(mm, address, pte, swp_entry_to_pte(make_hwpoison_entry(page))); } else if (PageAnon(page)) { swp_entry_t entry = { .val = page_private(page) }; if (PageSwapCache(page)) { /* * Store the swap location in the pte. * See handle_pte_fault() ... */ if (swap_duplicate(entry) < 0) { set_pte_at(mm, address, pte, pteval); ret = SWAP_FAIL; goto out_unmap; } if (list_empty(&mm->mmlist)) { spin_lock(&mmlist_lock); if (list_empty(&mm->mmlist)) list_add(&mm->mmlist, &init_mm.mmlist); spin_unlock(&mmlist_lock); } dec_mm_counter(mm, MM_ANONPAGES); inc_mm_counter(mm, MM_SWAPENTS); } else if (PAGE_MIGRATION) { /* * Store the pfn of the page in a special migration * pte. do_swap_page() will wait until the migration * pte is removed and then restart fault handling. */ BUG_ON(TTU_ACTION(flags) != TTU_MIGRATION); entry = make_migration_entry(page, pte_write(pteval)); } set_pte_at(mm, address, pte, swp_entry_to_pte(entry)); BUG_ON(pte_file(*pte)); } else if (PAGE_MIGRATION && (TTU_ACTION(flags) == TTU_MIGRATION)) { /* Establish migration entry for a file page */ swp_entry_t entry; entry = make_migration_entry(page, pte_write(pteval)); set_pte_at(mm, address, pte, swp_entry_to_pte(entry)); } else dec_mm_counter(mm, MM_FILEPAGES); page_remove_rmap(page); page_cache_release(page); out_unmap: pte_unmap_unlock(pte, ptl); out: return ret; out_mlock: pte_unmap_unlock(pte, ptl); /* * We need mmap_sem locking, Otherwise VM_LOCKED check makes * unstable result and race. Plus, We can't wait here because * we now hold anon_vma->lock or mapping->i_mmap_mutex. * if trylock failed, the page remain in evictable lru and later * vmscan could retry to move the page to unevictable lru if the * page is actually mlocked. */ if (down_read_trylock(&vma->vm_mm->mmap_sem)) { if (vma->vm_flags & VM_LOCKED) { mlock_vma_page(page); ret = SWAP_MLOCK; } up_read(&vma->vm_mm->mmap_sem); } return ret; } /* * objrmap doesn't work for nonlinear VMAs because the assumption that * offset-into-file correlates with offset-into-virtual-addresses does not hold. * Consequently, given a particular page and its ->index, we cannot locate the * ptes which are mapping that page without an exhaustive linear search. * * So what this code does is a mini "virtual scan" of each nonlinear VMA which * maps the file to which the target page belongs. The ->vm_private_data field * holds the current cursor into that scan. Successive searches will circulate * around the vma's virtual address space. * * So as more replacement pressure is applied to the pages in a nonlinear VMA, * more scanning pressure is placed against them as well. Eventually pages * will become fully unmapped and are eligible for eviction. * * For very sparsely populated VMAs this is a little inefficient - chances are * there there won't be many ptes located within the scan cluster. In this case * maybe we could scan further - to the end of the pte page, perhaps. * * Mlocked pages: check VM_LOCKED under mmap_sem held for read, if we can * acquire it without blocking. If vma locked, mlock the pages in the cluster, * rather than unmapping them. If we encounter the "check_page" that vmscan is * trying to unmap, return SWAP_MLOCK, else default SWAP_AGAIN. */ #define CLUSTER_SIZE min(32*PAGE_SIZE, PMD_SIZE) #define CLUSTER_MASK (~(CLUSTER_SIZE - 1)) static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount, struct vm_area_struct *vma, struct page *check_page) { struct mm_struct *mm = vma->vm_mm; pgd_t *pgd; pud_t *pud; pmd_t *pmd; pte_t *pte; pte_t pteval; spinlock_t *ptl; struct page *page; unsigned long address; unsigned long end; int ret = SWAP_AGAIN; int locked_vma = 0; address = (vma->vm_start + cursor) & CLUSTER_MASK; end = address + CLUSTER_SIZE; if (address < vma->vm_start) address = vma->vm_start; if (end > vma->vm_end) end = vma->vm_end; pgd = pgd_offset(mm, address); if (!pgd_present(*pgd)) return ret; pud = pud_offset(pgd, address); if (!pud_present(*pud)) return ret; pmd = pmd_offset(pud, address); if (!pmd_present(*pmd)) return ret; /* * If we can acquire the mmap_sem for read, and vma is VM_LOCKED, * keep the sem while scanning the cluster for mlocking pages. */ if (down_read_trylock(&vma->vm_mm->mmap_sem)) { locked_vma = (vma->vm_flags & VM_LOCKED); if (!locked_vma) up_read(&vma->vm_mm->mmap_sem); /* don't need it */ } pte = pte_offset_map_lock(mm, pmd, address, &ptl); /* Update high watermark before we lower rss */ update_hiwater_rss(mm); for (; address < end; pte++, address += PAGE_SIZE) { if (!pte_present(*pte)) continue; page = vm_normal_page(vma, address, *pte); BUG_ON(!page || PageAnon(page)); if (locked_vma) { mlock_vma_page(page); /* no-op if already mlocked */ if (page == check_page) ret = SWAP_MLOCK; continue; /* don't unmap */ } if (ptep_clear_flush_young_notify(vma, address, pte)) continue; /* Nuke the page table entry. */ flush_cache_page(vma, address, pte_pfn(*pte)); pteval = ptep_clear_flush_notify(vma, address, pte); /* If nonlinear, store the file page offset in the pte. */ if (page->index != linear_page_index(vma, address)) set_pte_at(mm, address, pte, pgoff_to_pte(page->index)); /* Move the dirty bit to the physical page now the pte is gone. */ if (pte_dirty(pteval)) set_page_dirty(page); page_remove_rmap(page); page_cache_release(page); dec_mm_counter(mm, MM_FILEPAGES); (*mapcount)--; } pte_unmap_unlock(pte - 1, ptl); if (locked_vma) up_read(&vma->vm_mm->mmap_sem); return ret; } bool is_vma_temporary_stack(struct vm_area_struct *vma) { int maybe_stack = vma->vm_flags & (VM_GROWSDOWN | VM_GROWSUP); if (!maybe_stack) return false; if ((vma->vm_flags & VM_STACK_INCOMPLETE_SETUP) == VM_STACK_INCOMPLETE_SETUP) return true; return false; } /** * try_to_unmap_anon - unmap or unlock anonymous page using the object-based * rmap method * @page: the page to unmap/unlock * @flags: action and flags * * Find all the mappings of a page using the mapping pointer and the vma chains * contained in the anon_vma struct it points to. * * This function is only called from try_to_unmap/try_to_munlock for * anonymous pages. * When called from try_to_munlock(), the mmap_sem of the mm containing the vma * where the page was found will be held for write. So, we won't recheck * vm_flags for that VMA. That should be OK, because that vma shouldn't be * 'LOCKED. */ static int try_to_unmap_anon(struct page *page, enum ttu_flags flags) { struct anon_vma *anon_vma; struct anon_vma_chain *avc; int ret = SWAP_AGAIN; anon_vma = page_lock_anon_vma(page); if (!anon_vma) return ret; list_for_each_entry(avc, &anon_vma->head, same_anon_vma) { struct vm_area_struct *vma = avc->vma; unsigned long address; /* * During exec, a temporary VMA is setup and later moved. * The VMA is moved under the anon_vma lock but not the * page tables leading to a race where migration cannot * find the migration ptes. Rather than increasing the * locking requirements of exec(), migration skips * temporary VMAs until after exec() completes. */ if (PAGE_MIGRATION && (flags & TTU_MIGRATION) && is_vma_temporary_stack(vma)) continue; address = vma_address(page, vma); if (address == -EFAULT) continue; ret = try_to_unmap_one(page, vma, address, flags); if (ret != SWAP_AGAIN || !page_mapped(page)) break; } page_unlock_anon_vma(anon_vma); return ret; } /** * try_to_unmap_file - unmap/unlock file page using the object-based rmap method * @page: the page to unmap/unlock * @flags: action and flags * * Find all the mappings of a page using the mapping pointer and the vma chains * contained in the address_space struct it points to. * * This function is only called from try_to_unmap/try_to_munlock for * object-based pages. * When called from try_to_munlock(), the mmap_sem of the mm containing the vma * where the page was found will be held for write. So, we won't recheck * vm_flags for that VMA. That should be OK, because that vma shouldn't be * 'LOCKED. */ static int try_to_unmap_file(struct page *page, enum ttu_flags flags) { struct address_space *mapping = page->mapping; pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); struct vm_area_struct *vma; struct prio_tree_iter iter; int ret = SWAP_AGAIN; unsigned long cursor; unsigned long max_nl_cursor = 0; unsigned long max_nl_size = 0; unsigned int mapcount; mutex_lock(&mapping->i_mmap_mutex); vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) { unsigned long address = vma_address(page, vma); if (address == -EFAULT) continue; ret = try_to_unmap_one(page, vma, address, flags); if (ret != SWAP_AGAIN || !page_mapped(page)) goto out; } if (list_empty(&mapping->i_mmap_nonlinear)) goto out; /* * We don't bother to try to find the munlocked page in nonlinears. * It's costly. Instead, later, page reclaim logic may call * try_to_unmap(TTU_MUNLOCK) and recover PG_mlocked lazily. */ if (TTU_ACTION(flags) == TTU_MUNLOCK) goto out; list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list) { cursor = (unsigned long) vma->vm_private_data; if (cursor > max_nl_cursor) max_nl_cursor = cursor; cursor = vma->vm_end - vma->vm_start; if (cursor > max_nl_size) max_nl_size = cursor; } if (max_nl_size == 0) { /* all nonlinears locked or reserved ? */ ret = SWAP_FAIL; goto out; } /* * We don't try to search for this page in the nonlinear vmas, * and page_referenced wouldn't have found it anyway. Instead * just walk the nonlinear vmas trying to age and unmap some. * The mapcount of the page we came in with is irrelevant, * but even so use it as a guide to how hard we should try? */ mapcount = page_mapcount(page); if (!mapcount) goto out; cond_resched(); max_nl_size = (max_nl_size + CLUSTER_SIZE - 1) & CLUSTER_MASK; if (max_nl_cursor == 0) max_nl_cursor = CLUSTER_SIZE; do { list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list) { cursor = (unsigned long) vma->vm_private_data; while ( cursor < max_nl_cursor && cursor < vma->vm_end - vma->vm_start) { if (try_to_unmap_cluster(cursor, &mapcount, vma, page) == SWAP_MLOCK) ret = SWAP_MLOCK; cursor += CLUSTER_SIZE; vma->vm_private_data = (void *) cursor; if ((int)mapcount <= 0) goto out; } vma->vm_private_data = (void *) max_nl_cursor; } cond_resched(); max_nl_cursor += CLUSTER_SIZE; } while (max_nl_cursor <= max_nl_size); /* * Don't loop forever (perhaps all the remaining pages are * in locked vmas). Reset cursor on all unreserved nonlinear * vmas, now forgetting on which ones it had fallen behind. */ list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list) vma->vm_private_data = NULL; out: mutex_unlock(&mapping->i_mmap_mutex); return ret; } /** * try_to_unmap - try to remove all page table mappings to a page * @page: the page to get unmapped * @flags: action and flags * * Tries to remove all the page table entries which are mapping this * page, used in the pageout path. Caller must hold the page lock. * Return values are: * * SWAP_SUCCESS - we succeeded in removing all mappings * SWAP_AGAIN - we missed a mapping, try again later * SWAP_FAIL - the page is unswappable * SWAP_MLOCK - page is mlocked. */ int try_to_unmap(struct page *page, enum ttu_flags flags) { int ret; BUG_ON(!PageLocked(page)); VM_BUG_ON(!PageHuge(page) && PageTransHuge(page)); if (unlikely(PageKsm(page))) ret = try_to_unmap_ksm(page, flags); else if (PageAnon(page)) ret = try_to_unmap_anon(page, flags); else ret = try_to_unmap_file(page, flags); if (ret != SWAP_MLOCK && !page_mapped(page)) ret = SWAP_SUCCESS; return ret; } /** * try_to_munlock - try to munlock a page * @page: the page to be munlocked * * Called from munlock code. Checks all of the VMAs mapping the page * to make sure nobody else has this page mlocked. The page will be * returned with PG_mlocked cleared if no other vmas have it mlocked. * * Return values are: * * SWAP_AGAIN - no vma is holding page mlocked, or, * SWAP_AGAIN - page mapped in mlocked vma -- couldn't acquire mmap sem * SWAP_FAIL - page cannot be located at present * SWAP_MLOCK - page is now mlocked. */ int try_to_munlock(struct page *page) { VM_BUG_ON(!PageLocked(page) || PageLRU(page)); if (unlikely(PageKsm(page))) return try_to_unmap_ksm(page, TTU_MUNLOCK); else if (PageAnon(page)) return try_to_unmap_anon(page, TTU_MUNLOCK); else return try_to_unmap_file(page, TTU_MUNLOCK); } void __put_anon_vma(struct anon_vma *anon_vma) { struct anon_vma *root = anon_vma->root; if (root != anon_vma && atomic_dec_and_test(&root->refcount)) anon_vma_free(root); anon_vma_free(anon_vma); } #ifdef CONFIG_MIGRATION /* * rmap_walk() and its helpers rmap_walk_anon() and rmap_walk_file(): * Called by migrate.c to remove migration ptes, but might be used more later. */ static int rmap_walk_anon(struct page *page, int (*rmap_one)(struct page *, struct vm_area_struct *, unsigned long, void *), void *arg) { struct anon_vma *anon_vma; struct anon_vma_chain *avc; int ret = SWAP_AGAIN; /* * Note: remove_migration_ptes() cannot use page_lock_anon_vma() * because that depends on page_mapped(); but not all its usages * are holding mmap_sem. Users without mmap_sem are required to * take a reference count to prevent the anon_vma disappearing */ anon_vma = page_anon_vma(page); if (!anon_vma) return ret; anon_vma_lock(anon_vma); list_for_each_entry(avc, &anon_vma->head, same_anon_vma) { struct vm_area_struct *vma = avc->vma; unsigned long address = vma_address(page, vma); if (address == -EFAULT) continue; ret = rmap_one(page, vma, address, arg); if (ret != SWAP_AGAIN) break; } anon_vma_unlock(anon_vma); return ret; } static int rmap_walk_file(struct page *page, int (*rmap_one)(struct page *, struct vm_area_struct *, unsigned long, void *), void *arg) { struct address_space *mapping = page->mapping; pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); struct vm_area_struct *vma; struct prio_tree_iter iter; int ret = SWAP_AGAIN; if (!mapping) return ret; mutex_lock(&mapping->i_mmap_mutex); vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) { unsigned long address = vma_address(page, vma); if (address == -EFAULT) continue; ret = rmap_one(page, vma, address, arg); if (ret != SWAP_AGAIN) break; } /* * No nonlinear handling: being always shared, nonlinear vmas * never contain migration ptes. Decide what to do about this * limitation to linear when we need rmap_walk() on nonlinear. */ mutex_unlock(&mapping->i_mmap_mutex); return ret; } int rmap_walk(struct page *page, int (*rmap_one)(struct page *, struct vm_area_struct *, unsigned long, void *), void *arg) { VM_BUG_ON(!PageLocked(page)); if (unlikely(PageKsm(page))) return rmap_walk_ksm(page, rmap_one, arg); else if (PageAnon(page)) return rmap_walk_anon(page, rmap_one, arg); else return rmap_walk_file(page, rmap_one, arg); } #endif /* CONFIG_MIGRATION */ #ifdef CONFIG_HUGETLB_PAGE /* * The following three functions are for anonymous (private mapped) hugepages. * Unlike common anonymous pages, anonymous hugepages have no accounting code * and no lru code, because we handle hugepages differently from common pages. */ static void __hugepage_set_anon_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address, int exclusive) { struct anon_vma *anon_vma = vma->anon_vma; BUG_ON(!anon_vma); if (PageAnon(page)) return; if (!exclusive) anon_vma = anon_vma->root; anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON; page->mapping = (struct address_space *) anon_vma; page->index = linear_page_index(vma, address); } void hugepage_add_anon_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address) { struct anon_vma *anon_vma = vma->anon_vma; int first; BUG_ON(!PageLocked(page)); BUG_ON(!anon_vma); BUG_ON(address < vma->vm_start || address >= vma->vm_end); first = atomic_inc_and_test(&page->_mapcount); if (first) __hugepage_set_anon_rmap(page, vma, address, 0); } void hugepage_add_new_anon_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address) { BUG_ON(address < vma->vm_start || address >= vma->vm_end); atomic_set(&page->_mapcount, 0); __hugepage_set_anon_rmap(page, vma, address, 1); } #endif /* CONFIG_HUGETLB_PAGE */