diff options
Diffstat (limited to 'mm/ksm.c')
| -rw-r--r-- | mm/ksm.c | 1489 |
1 files changed, 1484 insertions, 5 deletions
@@ -1,11 +1,1285 @@ /* - * Initial dummy version just to illustrate KSM's interface to other files. + * Memory merging support. + * + * This code enables dynamic sharing of identical pages found in different + * memory areas, even if they are not shared by fork() + * + * Copyright (C) 2008 Red Hat, Inc. + * Authors: + * Izik Eidus + * Andrea Arcangeli + * Chris Wright + * + * This work is licensed under the terms of the GNU GPL, version 2. */ #include <linux/errno.h> +#include <linux/mm.h> +#include <linux/fs.h> #include <linux/mman.h> +#include <linux/sched.h> +#include <linux/rwsem.h> +#include <linux/pagemap.h> +#include <linux/rmap.h> +#include <linux/spinlock.h> +#include <linux/jhash.h> +#include <linux/delay.h> +#include <linux/kthread.h> +#include <linux/wait.h> +#include <linux/slab.h> +#include <linux/rbtree.h> +#include <linux/mmu_notifier.h> #include <linux/ksm.h> +#include <asm/tlbflush.h> + +/* + * A few notes about the KSM scanning process, + * to make it easier to understand the data structures below: + * + * In order to reduce excessive scanning, KSM sorts the memory pages by their + * contents into a data structure that holds pointers to the pages' locations. + * + * Since the contents of the pages may change at any moment, KSM cannot just + * insert the pages into a normal sorted tree and expect it to find anything. + * Therefore KSM uses two data structures - the stable and the unstable tree. + * + * The stable tree holds pointers to all the merged pages (ksm pages), sorted + * by their contents. Because each such page is write-protected, searching on + * this tree is fully assured to be working (except when pages are unmapped), + * and therefore this tree is called the stable tree. + * + * In addition to the stable tree, KSM uses a second data structure called the + * unstable tree: this tree holds pointers to pages which have been found to + * be "unchanged for a period of time". The unstable tree sorts these pages + * by their contents, but since they are not write-protected, KSM cannot rely + * upon the unstable tree to work correctly - the unstable tree is liable to + * be corrupted as its contents are modified, and so it is called unstable. + * + * KSM solves this problem by several techniques: + * + * 1) The unstable tree is flushed every time KSM completes scanning all + * memory areas, and then the tree is rebuilt again from the beginning. + * 2) KSM will only insert into the unstable tree, pages whose hash value + * has not changed since the previous scan of all memory areas. + * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the + * colors of the nodes and not on their contents, assuring that even when + * the tree gets "corrupted" it won't get out of balance, so scanning time + * remains the same (also, searching and inserting nodes in an rbtree uses + * the same algorithm, so we have no overhead when we flush and rebuild). + * 4) KSM never flushes the stable tree, which means that even if it were to + * take 10 attempts to find a page in the unstable tree, once it is found, + * it is secured in the stable tree. (When we scan a new page, we first + * compare it against the stable tree, and then against the unstable tree.) + */ + +/** + * struct mm_slot - ksm information per mm that is being scanned + * @link: link to the mm_slots hash list + * @mm_list: link into the mm_slots list, rooted in ksm_mm_head + * @rmap_list: head for this mm_slot's list of rmap_items + * @mm: the mm that this information is valid for + */ +struct mm_slot { + struct hlist_node link; + struct list_head mm_list; + struct list_head rmap_list; + struct mm_struct *mm; +}; + +/** + * struct ksm_scan - cursor for scanning + * @mm_slot: the current mm_slot we are scanning + * @address: the next address inside that to be scanned + * @rmap_item: the current rmap that we are scanning inside the rmap_list + * @seqnr: count of completed full scans (needed when removing unstable node) + * + * There is only the one ksm_scan instance of this cursor structure. + */ +struct ksm_scan { + struct mm_slot *mm_slot; + unsigned long address; + struct rmap_item *rmap_item; + unsigned long seqnr; +}; + +/** + * struct rmap_item - reverse mapping item for virtual addresses + * @link: link into mm_slot's rmap_list (rmap_list is per mm) + * @mm: the memory structure this rmap_item is pointing into + * @address: the virtual address this rmap_item tracks (+ flags in low bits) + * @oldchecksum: previous checksum of the page at that virtual address + * @node: rb_node of this rmap_item in either unstable or stable tree + * @next: next rmap_item hanging off the same node of the stable tree + * @prev: previous rmap_item hanging off the same node of the stable tree + */ +struct rmap_item { + struct list_head link; + struct mm_struct *mm; + unsigned long address; /* + low bits used for flags below */ + union { + unsigned int oldchecksum; /* when unstable */ + struct rmap_item *next; /* when stable */ + }; + union { + struct rb_node node; /* when tree node */ + struct rmap_item *prev; /* in stable list */ + }; +}; + +#define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */ +#define NODE_FLAG 0x100 /* is a node of unstable or stable tree */ +#define STABLE_FLAG 0x200 /* is a node or list item of stable tree */ + +/* The stable and unstable tree heads */ +static struct rb_root root_stable_tree = RB_ROOT; +static struct rb_root root_unstable_tree = RB_ROOT; + +#define MM_SLOTS_HASH_HEADS 1024 +static struct hlist_head *mm_slots_hash; + +static struct mm_slot ksm_mm_head = { + .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list), +}; +static struct ksm_scan ksm_scan = { + .mm_slot = &ksm_mm_head, +}; + +static struct kmem_cache *rmap_item_cache; +static struct kmem_cache *mm_slot_cache; + +/* The number of nodes in the stable tree */ +static unsigned long ksm_kernel_pages_allocated; + +/* The number of page slots sharing those nodes */ +static unsigned long ksm_pages_shared; + +/* Limit on the number of unswappable pages used */ +static unsigned long ksm_max_kernel_pages; + +/* Number of pages ksmd should scan in one batch */ +static unsigned int ksm_thread_pages_to_scan; + +/* Milliseconds ksmd should sleep between batches */ +static unsigned int ksm_thread_sleep_millisecs; + +#define KSM_RUN_STOP 0 +#define KSM_RUN_MERGE 1 +#define KSM_RUN_UNMERGE 2 +static unsigned int ksm_run; + +static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait); +static DEFINE_MUTEX(ksm_thread_mutex); +static DEFINE_SPINLOCK(ksm_mmlist_lock); + +#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\ + sizeof(struct __struct), __alignof__(struct __struct),\ + (__flags), NULL) + +static int __init ksm_slab_init(void) +{ + rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0); + if (!rmap_item_cache) + goto out; + + mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0); + if (!mm_slot_cache) + goto out_free; + + return 0; + +out_free: + kmem_cache_destroy(rmap_item_cache); +out: + return -ENOMEM; +} + +static void __init ksm_slab_free(void) +{ + kmem_cache_destroy(mm_slot_cache); + kmem_cache_destroy(rmap_item_cache); + mm_slot_cache = NULL; +} + +static inline struct rmap_item *alloc_rmap_item(void) +{ + return kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL); +} + +static inline void free_rmap_item(struct rmap_item *rmap_item) +{ + rmap_item->mm = NULL; /* debug safety */ + kmem_cache_free(rmap_item_cache, rmap_item); +} + +static inline struct mm_slot *alloc_mm_slot(void) +{ + if (!mm_slot_cache) /* initialization failed */ + return NULL; + return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL); +} + +static inline void free_mm_slot(struct mm_slot *mm_slot) +{ + kmem_cache_free(mm_slot_cache, mm_slot); +} + +static int __init mm_slots_hash_init(void) +{ + mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head), + GFP_KERNEL); + if (!mm_slots_hash) + return -ENOMEM; + return 0; +} + +static void __init mm_slots_hash_free(void) +{ + kfree(mm_slots_hash); +} + +static struct mm_slot *get_mm_slot(struct mm_struct *mm) +{ + struct mm_slot *mm_slot; + struct hlist_head *bucket; + struct hlist_node *node; + + bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct)) + % MM_SLOTS_HASH_HEADS]; + hlist_for_each_entry(mm_slot, node, bucket, link) { + if (mm == mm_slot->mm) + return mm_slot; + } + return NULL; +} + +static void insert_to_mm_slots_hash(struct mm_struct *mm, + struct mm_slot *mm_slot) +{ + struct hlist_head *bucket; + + bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct)) + % MM_SLOTS_HASH_HEADS]; + mm_slot->mm = mm; + INIT_LIST_HEAD(&mm_slot->rmap_list); + hlist_add_head(&mm_slot->link, bucket); +} + +static inline int in_stable_tree(struct rmap_item *rmap_item) +{ + return rmap_item->address & STABLE_FLAG; +} + +/* + * We use break_ksm to break COW on a ksm page: it's a stripped down + * + * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1) + * put_page(page); + * + * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma, + * in case the application has unmapped and remapped mm,addr meanwhile. + * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP + * mmap of /dev/mem or /dev/kmem, where we would not want to touch it. + */ +static void break_ksm(struct vm_area_struct *vma, unsigned long addr) +{ + struct page *page; + int ret; + + do { + cond_resched(); + page = follow_page(vma, addr, FOLL_GET); + if (!page) + break; + if (PageKsm(page)) + ret = handle_mm_fault(vma->vm_mm, vma, addr, + FAULT_FLAG_WRITE); + else + ret = VM_FAULT_WRITE; + put_page(page); + } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS))); + + /* Which leaves us looping there if VM_FAULT_OOM: hmmm... */ +} + +static void __break_cow(struct mm_struct *mm, unsigned long addr) +{ + struct vm_area_struct *vma; + + vma = find_vma(mm, addr); + if (!vma || vma->vm_start > addr) + return; + if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) + return; + break_ksm(vma, addr); +} + +static void break_cow(struct mm_struct *mm, unsigned long addr) +{ + down_read(&mm->mmap_sem); + __break_cow(mm, addr); + up_read(&mm->mmap_sem); +} + +static struct page *get_mergeable_page(struct rmap_item *rmap_item) +{ + struct mm_struct *mm = rmap_item->mm; + unsigned long addr = rmap_item->address; + struct vm_area_struct *vma; + struct page *page; + + down_read(&mm->mmap_sem); + vma = find_vma(mm, addr); + if (!vma || vma->vm_start > addr) + goto out; + if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) + goto out; + + page = follow_page(vma, addr, FOLL_GET); + if (!page) + goto out; + if (PageAnon(page)) { + flush_anon_page(vma, page, addr); + flush_dcache_page(page); + } else { + put_page(page); +out: page = NULL; + } + up_read(&mm->mmap_sem); + return page; +} + +/* + * get_ksm_page: checks if the page at the virtual address in rmap_item + * is still PageKsm, in which case we can trust the content of the page, + * and it returns the gotten page; but NULL if the page has been zapped. + */ +static struct page *get_ksm_page(struct rmap_item *rmap_item) +{ + struct page *page; + + page = get_mergeable_page(rmap_item); + if (page && !PageKsm(page)) { + put_page(page); + page = NULL; + } + return page; +} + +/* + * Removing rmap_item from stable or unstable tree. + * This function will clean the information from the stable/unstable tree. + */ +static void remove_rmap_item_from_tree(struct rmap_item *rmap_item) +{ + if (in_stable_tree(rmap_item)) { + struct rmap_item *next_item = rmap_item->next; + + if (rmap_item->address & NODE_FLAG) { + if (next_item) { + rb_replace_node(&rmap_item->node, + &next_item->node, + &root_stable_tree); + next_item->address |= NODE_FLAG; + } else { + rb_erase(&rmap_item->node, &root_stable_tree); + ksm_kernel_pages_allocated--; + } + } else { + struct rmap_item *prev_item = rmap_item->prev; + + BUG_ON(prev_item->next != rmap_item); + prev_item->next = next_item; + if (next_item) { + BUG_ON(next_item->prev != rmap_item); + next_item->prev = rmap_item->prev; + } + } + + rmap_item->next = NULL; + ksm_pages_shared--; + + } else if (rmap_item->address & NODE_FLAG) { + unsigned char age; + /* + * ksm_thread can and must skip the rb_erase, because + * root_unstable_tree was already reset to RB_ROOT. + * But __ksm_exit has to be careful: do the rb_erase + * if it's interrupting a scan, and this rmap_item was + * inserted by this scan rather than left from before. + * + * Because of the case in which remove_mm_from_lists + * increments seqnr before removing rmaps, unstable_nr + * may even be 2 behind seqnr, but should never be + * further behind. Yes, I did have trouble with this! + */ + age = (unsigned char)(ksm_scan.seqnr - rmap_item->address); + BUG_ON(age > 2); + if (!age) + rb_erase(&rmap_item->node, &root_unstable_tree); + } + + rmap_item->address &= PAGE_MASK; + + cond_resched(); /* we're called from many long loops */ +} + +static void remove_all_slot_rmap_items(struct mm_slot *mm_slot) +{ + struct rmap_item *rmap_item, *node; + + list_for_each_entry_safe(rmap_item, node, &mm_slot->rmap_list, link) { + remove_rmap_item_from_tree(rmap_item); + list_del(&rmap_item->link); + free_rmap_item(rmap_item); + } +} + +static void remove_trailing_rmap_items(struct mm_slot *mm_slot, + struct list_head *cur) +{ + struct rmap_item *rmap_item; + + while (cur != &mm_slot->rmap_list) { + rmap_item = list_entry(cur, struct rmap_item, link); + cur = cur->next; + remove_rmap_item_from_tree(rmap_item); + list_del(&rmap_item->link); + free_rmap_item(rmap_item); + } +} + +/* + * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather + * than check every pte of a given vma, the locking doesn't quite work for + * that - an rmap_item is assigned to the stable tree after inserting ksm + * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing + * rmap_items from parent to child at fork time (so as not to waste time + * if exit comes before the next scan reaches it). + */ +static void unmerge_ksm_pages(struct vm_area_struct *vma, + unsigned long start, unsigned long end) +{ + unsigned long addr; + + for (addr = start; addr < end; addr += PAGE_SIZE) + break_ksm(vma, addr); +} + +static void unmerge_and_remove_all_rmap_items(void) +{ + struct mm_slot *mm_slot; + struct mm_struct *mm; + struct vm_area_struct *vma; + + list_for_each_entry(mm_slot, &ksm_mm_head.mm_list, mm_list) { + mm = mm_slot->mm; + down_read(&mm->mmap_sem); + for (vma = mm->mmap; vma; vma = vma->vm_next) { + if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) + continue; + unmerge_ksm_pages(vma, vma->vm_start, vma->vm_end); + } + remove_all_slot_rmap_items(mm_slot); + up_read(&mm->mmap_sem); + } + + spin_lock(&ksm_mmlist_lock); + if (ksm_scan.mm_slot != &ksm_mm_head) { + ksm_scan.mm_slot = &ksm_mm_head; + ksm_scan.seqnr++; + } + spin_unlock(&ksm_mmlist_lock); +} + +static void remove_mm_from_lists(struct mm_struct *mm) +{ + struct mm_slot *mm_slot; + + spin_lock(&ksm_mmlist_lock); + mm_slot = get_mm_slot(mm); + + /* + * This mm_slot is always at the scanning cursor when we're + * called from scan_get_next_rmap_item; but it's a special + * case when we're called from __ksm_exit. + */ + if (ksm_scan.mm_slot == mm_slot) { + ksm_scan.mm_slot = list_entry( + mm_slot->mm_list.next, struct mm_slot, mm_list); + ksm_scan.address = 0; + ksm_scan.rmap_item = list_entry( + &ksm_scan.mm_slot->rmap_list, struct rmap_item, link); + if (ksm_scan.mm_slot == &ksm_mm_head) + ksm_scan.seqnr++; + } + + hlist_del(&mm_slot->link); + list_del(&mm_slot->mm_list); + spin_unlock(&ksm_mmlist_lock); + + remove_all_slot_rmap_items(mm_slot); + free_mm_slot(mm_slot); + clear_bit(MMF_VM_MERGEABLE, &mm->flags); +} + +static u32 calc_checksum(struct page *page) +{ + u32 checksum; + void *addr = kmap_atomic(page, KM_USER0); + checksum = jhash2(addr, PAGE_SIZE / 4, 17); + kunmap_atomic(addr, KM_USER0); + return checksum; +} + +static int memcmp_pages(struct page *page1, struct page *page2) +{ + char *addr1, *addr2; + int ret; + + addr1 = kmap_atomic(page1, KM_USER0); + addr2 = kmap_atomic(page2, KM_USER1); + ret = memcmp(addr1, addr2, PAGE_SIZE); + kunmap_atomic(addr2, KM_USER1); + kunmap_atomic(addr1, KM_USER0); + return ret; +} + +static inline int pages_identical(struct page *page1, struct page *page2) +{ + return !memcmp_pages(page1, page2); +} + +static int write_protect_page(struct vm_area_struct *vma, struct page *page, + pte_t *orig_pte) +{ + struct mm_struct *mm = vma->vm_mm; + unsigned long addr; + pte_t *ptep; + spinlock_t *ptl; + int swapped; + int err = -EFAULT; + + addr = page_address_in_vma(page, vma); + if (addr == -EFAULT) + goto out; + + ptep = page_check_address(page, mm, addr, &ptl, 0); + if (!ptep) + goto out; + + if (pte_write(*ptep)) { + pte_t entry; + + swapped = PageSwapCache(page); + flush_cache_page(vma, addr, page_to_pfn(page)); + /* + * Ok this is tricky, when get_user_pages_fast() run it doesnt + * take any lock, therefore the check that we are going to make + * with the pagecount against the mapcount is racey and + * O_DIRECT can happen right after the check. + * So we clear the pte and flush the tlb before the check + * this assure us that no O_DIRECT can happen after the check + * or in the middle of the check. + */ + entry = ptep_clear_flush(vma, addr, ptep); + /* + * Check that no O_DIRECT or similar I/O is in progress on the + * page + */ + if ((page_mapcount(page) + 2 + swapped) != page_count(page)) { + set_pte_at_notify(mm, addr, ptep, entry); + goto out_unlock; + } + entry = pte_wrprotect(entry); + set_pte_at_notify(mm, addr, ptep, entry); + } + *orig_pte = *ptep; + err = 0; + +out_unlock: + pte_unmap_unlock(ptep, ptl); +out: + return err; +} + +/** + * replace_page - replace page in vma by new ksm page + * @vma: vma that holds the pte pointing to oldpage + * @oldpage: the page we are replacing by newpage + * @newpage: the ksm page we replace oldpage by + * @orig_pte: the original value of the pte + * + * Returns 0 on success, -EFAULT on failure. + */ +static int replace_page(struct vm_area_struct *vma, struct page *oldpage, + struct page *newpage, pte_t orig_pte) +{ + struct mm_struct *mm = vma->vm_mm; + pgd_t *pgd; + pud_t *pud; + pmd_t *pmd; + pte_t *ptep; + spinlock_t *ptl; + unsigned long addr; + pgprot_t prot; + int err = -EFAULT; + + prot = vm_get_page_prot(vma->vm_flags & ~VM_WRITE); + + addr = page_address_in_vma(oldpage, vma); + if (addr == -EFAULT) + goto out; + + pgd = pgd_offset(mm, addr); + if (!pgd_present(*pgd)) + goto out; + + pud = pud_offset(pgd, addr); + if (!pud_present(*pud)) + goto out; + + pmd = pmd_offset(pud, addr); + if (!pmd_present(*pmd)) + goto out; + + ptep = pte_offset_map_lock(mm, pmd, addr, &ptl); + if (!pte_same(*ptep, orig_pte)) { + pte_unmap_unlock(ptep, ptl); + goto out; + } + + get_page(newpage); + page_add_ksm_rmap(newpage); + + flush_cache_page(vma, addr, pte_pfn(*ptep)); + ptep_clear_flush(vma, addr, ptep); + set_pte_at_notify(mm, addr, ptep, mk_pte(newpage, prot)); + + page_remove_rmap(oldpage); + put_page(oldpage); + + pte_unmap_unlock(ptep, ptl); + err = 0; +out: + return err; +} + +/* + * try_to_merge_one_page - take two pages and merge them into one + * @vma: the vma that hold the pte pointing into oldpage + * @oldpage: the page that we want to replace with newpage + * @newpage: the page that we want to map instead of oldpage + * + * Note: + * oldpage should be a PageAnon page, while newpage should be a PageKsm page, + * or a newly allocated kernel page which page_add_ksm_rmap will make PageKsm. + * + * This function returns 0 if the pages were merged, -EFAULT otherwise. + */ +static int try_to_merge_one_page(struct vm_area_struct *vma, + struct page *oldpage, + struct page *newpage) +{ + pte_t orig_pte = __pte(0); + int err = -EFAULT; + + if (!(vma->vm_flags & VM_MERGEABLE)) + goto out; + + if (!PageAnon(oldpage)) + goto out; + + get_page(newpage); + get_page(oldpage); + + /* + * We need the page lock to read a stable PageSwapCache in + * write_protect_page(). We use trylock_page() instead of + * lock_page() because we don't want to wait here - we + * prefer to continue scanning and merging different pages, + * then come back to this page when it is unlocked. + */ + if (!trylock_page(oldpage)) + goto out_putpage; + /* + * If this anonymous page is mapped only here, its pte may need + * to be write-protected. If it's mapped elsewhere, all of its + * ptes are necessarily already write-protected. But in either + * case, we need to lock and check page_count is not raised. + */ + if (write_protect_page(vma, oldpage, &orig_pte)) { + unlock_page(oldpage); + goto out_putpage; + } + unlock_page(oldpage); + + if (pages_identical(oldpage, newpage)) + err = replace_page(vma, oldpage, newpage, orig_pte); + +out_putpage: + put_page(oldpage); + put_page(newpage); +out: + return err; +} + +/* + * try_to_merge_two_pages - take two identical pages and prepare them + * to be merged into one page. + * + * This function returns 0 if we successfully mapped two identical pages + * into one page, -EFAULT otherwise. + * + * Note that this function allocates a new kernel page: if one of the pages + * is already a ksm page, try_to_merge_with_ksm_page should be used. + */ +static int try_to_merge_two_pages(struct mm_struct *mm1, unsigned long addr1, + struct page *page1, struct mm_struct *mm2, + unsigned long addr2, struct page *page2) +{ + struct vm_area_struct *vma; + struct page *kpage; + int err = -EFAULT; + + /* + * The number of nodes in the stable tree + * is the number of kernel pages that we hold. + */ + if (ksm_max_kernel_pages && + ksm_max_kernel_pages <= ksm_kernel_pages_allocated) + return err; + + kpage = alloc_page(GFP_HIGHUSER); + if (!kpage) + return err; + + down_read(&mm1->mmap_sem); + vma = find_vma(mm1, addr1); + if (!vma || vma->vm_start > addr1) { + put_page(kpage); + up_read(&mm1->mmap_sem); + return err; + } + + copy_user_highpage(kpage, page1, addr1, vma); + err = try_to_merge_one_page(vma, page1, kpage); + up_read(&mm1->mmap_sem); + + if (!err) { + down_read(&mm2->mmap_sem); + vma = find_vma(mm2, addr2); + if (!vma || vma->vm_start > addr2) { + put_page(kpage); + up_read(&mm2->mmap_sem); + break_cow(mm1, addr1); + return -EFAULT; + } + + err = try_to_merge_one_page(vma, page2, kpage); + up_read(&mm2->mmap_sem); + + /* + * If the second try_to_merge_one_page failed, we have a + * ksm page with just one pte pointing to it, so break it. + */ + if (err) + break_cow(mm1, addr1); + else + ksm_pages_shared += 2; + } + + put_page(kpage); + return err; +} + +/* + * try_to_merge_with_ksm_page - like try_to_merge_two_pages, + * but no new kernel page is allocated: kpage must already be a ksm page. + */ +static int try_to_merge_with_ksm_page(struct mm_struct *mm1, + unsigned long addr1, + struct page *page1, + struct page *kpage) +{ + struct vm_area_struct *vma; + int err = -EFAULT; + + down_read(&mm1->mmap_sem); + vma = find_vma(mm1, addr1); + if (!vma || vma->vm_start > addr1) { + up_read(&mm1->mmap_sem); + return err; + } + + err = try_to_merge_one_page(vma, page1, kpage); + up_read(&mm1->mmap_sem); + + if (!err) + ksm_pages_shared++; + + return err; +} + +/* + * stable_tree_search - search page inside the stable tree + * @page: the page that we are searching identical pages to. + * @page2: pointer into identical page that we are holding inside the stable + * tree that we have found. + * @rmap_item: the reverse mapping item + * + * This function checks if there is a page inside the stable tree + * with identical content to the page that we are scanning right now. + * + * This function return rmap_item pointer to the identical item if found, + * NULL otherwise. + */ +static struct rmap_item *stable_tree_search(struct page *page, + struct page **page2, + struct rmap_item *rmap_item) +{ + struct rb_node *node = root_stable_tree.rb_node; + + while (node) { + struct rmap_item *tree_rmap_item, *next_rmap_item; + int ret; + + tree_rmap_item = rb_entry(node, struct rmap_item, node); + while (tree_rmap_item) { + BUG_ON(!in_stable_tree(tree_rmap_item)); + cond_resched(); + page2[0] = get_ksm_page(tree_rmap_item); + if (page2[0]) + break; + next_rmap_item = tree_rmap_item->next; + remove_rmap_item_from_tree(tree_rmap_item); + tree_rmap_item = next_rmap_item; + } + if (!tree_rmap_item) + return NULL; + + ret = memcmp_pages(page, page2[0]); + + if (ret < 0) { + put_page(page2[0]); + node = node->rb_left; + } else if (ret > 0) { + put_page(page2[0]); + node = node->rb_right; + } else { + return tree_rmap_item; + } + } + + return NULL; +} + +/* + * stable_tree_insert - insert rmap_item pointing to new ksm page + * into the stable tree. + * + * @page: the page that we are searching identical page to inside the stable + * tree. + * @rmap_item: pointer to the reverse mapping item. + * + * This function returns rmap_item if success, NULL otherwise. + */ +static struct rmap_item *stable_tree_insert(struct page *page, + struct rmap_item *rmap_item) +{ + struct rb_node **new = &root_stable_tree.rb_node; + struct rb_node *parent = NULL; + + while (*new) { + struct rmap_item *tree_rmap_item, *next_rmap_item; + struct page *tree_page; + int ret; + + tree_rmap_item = rb_entry(*new, struct rmap_item, node); + while (tree_rmap_item) { + BUG_ON(!in_stable_tree(tree_rmap_item)); + cond_resched(); + tree_page = get_ksm_page(tree_rmap_item); + if (tree_page) + break; + next_rmap_item = tree_rmap_item->next; + remove_rmap_item_from_tree(tree_rmap_item); + tree_rmap_item = next_rmap_item; + } + if (!tree_rmap_item) + return NULL; + + ret = memcmp_pages(page, tree_page); + put_page(tree_page); + + parent = *new; + if (ret < 0) + new = &parent->rb_left; + else if (ret > 0) + new = &parent->rb_right; + else { + /* + * It is not a bug that stable_tree_search() didn't + * find this node: because at that time our page was + * not yet write-protected, so may have changed since. + */ + return NULL; + } + } + + ksm_kernel_pages_allocated++; + + rmap_item->address |= NODE_FLAG | STABLE_FLAG; + rmap_item->next = NULL; + rb_link_node(&rmap_item->node, parent, new); + rb_insert_color(&rmap_item->node, &root_stable_tree); + + return rmap_item; +} + +/* + * unstable_tree_search_insert - search and insert items into the unstable tree. + * + * @page: the page that we are going to search for identical page or to insert + * into the unstable tree + * @page2: pointer into identical page that was found inside the unstable tree + * @rmap_item: the reverse mapping item of page + * + * This function searches for a page in the unstable tree identical to the + * page currently being scanned; and if no identical page is found in the + * tree, we insert rmap_item as a new object into the unstable tree. + * + * This function returns pointer to rmap_item found to be identical + * to the currently scanned page, NULL otherwise. + * + * This function does both searching and inserting, because they share + * the same walking algorithm in an rbtree. + */ +static struct rmap_item *unstable_tree_search_insert(struct page *page, + struct page **page2, + struct rmap_item *rmap_item) +{ + struct rb_node **new = &root_unstable_tree.rb_node; + struct rb_node *parent = NULL; + + while (*new) { + struct rmap_item *tree_rmap_item; + int ret; + + tree_rmap_item = rb_entry(*new, struct rmap_item, node); + page2[0] = get_mergeable_page(tree_rmap_item); + if (!page2[0]) + return NULL; + + /* + * Don't substitute an unswappable ksm page + * just for one good swappable forked page. + */ + if (page == page2[0]) { + put_page(page2[0]); + return NULL; + } + + ret = memcmp_pages(page, page2[0]); + + parent = *new; + if (ret < 0) { + put_page(page2[0]); + new = &parent->rb_left; + } else if (ret > 0) { + put_page(page2[0]); + new = &parent->rb_right; + } else { + return tree_rmap_item; + } + } + + rmap_item->address |= NODE_FLAG; + rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK); + rb_link_node(&rmap_item->node, parent, new); + rb_insert_color(&rmap_item->node, &root_unstable_tree); + + return NULL; +} + +/* + * stable_tree_append - add another rmap_item to the linked list of + * rmap_items hanging off a given node of the stable tree, all sharing + * the same ksm page. + */ +static void stable_tree_append(struct rmap_item *rmap_item, + struct rmap_item *tree_rmap_item) +{ + rmap_item->next = tree_rmap_item->next; + rmap_item->prev = tree_rmap_item; + + if (tree_rmap_item->next) + tree_rmap_item->next->prev = rmap_item; + + tree_rmap_item->next = rmap_item; + rmap_item->address |= STABLE_FLAG; +} + +/* + * cmp_and_merge_page - take a page computes its hash value and check if there + * is similar hash value to different page, + * in case we find that there is similar hash to different page we call to + * try_to_merge_two_pages(). + * + * @page: the page that we are searching identical page to. + * @rmap_item: the reverse mapping into the virtual address of this page + */ +static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) +{ + struct page *page2[1]; + struct rmap_item *tree_rmap_item; + unsigned int checksum; + int err; + + if (in_stable_tree(rmap_item)) + remove_rmap_item_from_tree(rmap_item); + + /* We first start with searching the page inside the stable tree */ + tree_rmap_item = stable_tree_search(page, page2, rmap_item); + if (tree_rmap_item) { + if (page == page2[0]) { /* forked */ + ksm_pages_shared++; + err = 0; + } else + err = try_to_merge_with_ksm_page(rmap_item->mm, + rmap_item->address, + page, page2[0]); + put_page(page2[0]); + + if (!err) { + /* + * The page was successfully merged: + * add its rmap_item to the stable tree. + */ + stable_tree_append(rmap_item, tree_rmap_item); + } + return; + } + + /* + * A ksm page might have got here by fork, but its other + * references have already been removed from the stable tree. + */ + if (PageKsm(page)) + break_cow(rmap_item->mm, rmap_item->address); + + /* + * In case the hash value of the page was changed from the last time we + * have calculated it, this page to be changed frequely, therefore we + * don't want to insert it to the unstable tree, and we don't want to + * waste our time to search if there is something identical to it there. + */ + checksum = calc_checksum(page); + if (rmap_item->oldchecksum != checksum) { + rmap_item->oldchecksum = checksum; + return; + } + + tree_rmap_item = unstable_tree_search_insert(page, page2, rmap_item); + if (tree_rmap_item) { + err = try_to_merge_two_pages(rmap_item->mm, + rmap_item->address, page, + tree_rmap_item->mm, + tree_rmap_item->address, page2[0]); + /* + * As soon as we merge this page, we want to remove the + * rmap_item of the page we have merged with from the unstable + * tree, and insert it instead as new node in the stable tree. + */ + if (!err) { + rb_erase(&tree_rmap_item->node, &root_unstable_tree); + tree_rmap_item->address &= ~NODE_FLAG; + /* + * If we fail to insert the page into the stable tree, + * we will have 2 virtual addresses that are pointing + * to a ksm page left outside the stable tree, + * in which case we need to break_cow on both. + */ + if (stable_tree_insert(page2[0], tree_rmap_item)) + stable_tree_append(rmap_item, tree_rmap_item); + else { + break_cow(tree_rmap_item->mm, + tree_rmap_item->address); + break_cow(rmap_item->mm, rmap_item->address); + ksm_pages_shared -= 2; + } + } + + put_page(page2[0]); + } +} + +static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot, + struct list_head *cur, + unsigned long addr) +{ + struct rmap_item *rmap_item; + + while (cur != &mm_slot->rmap_list) { + rmap_item = list_entry(cur, struct rmap_item, link); + if ((rmap_item->address & PAGE_MASK) == addr) { + if (!in_stable_tree(rmap_item)) + remove_rmap_item_from_tree(rmap_item); + return rmap_item; + } + if (rmap_item->address > addr) + break; + cur = cur->next; + remove_rmap_item_from_tree(rmap_item); + list_del(&rmap_item->link); + free_rmap_item(rmap_item); + } + + rmap_item = alloc_rmap_item(); + if (rmap_item) { + /* It has already been zeroed */ + rmap_item->mm = mm_slot->mm; + rmap_item->address = addr; + list_add_tail(&rmap_item->link, cur); + } + return rmap_item; +} + +static struct rmap_item *scan_get_next_rmap_item(struct page **page) +{ + struct mm_struct *mm; + struct mm_slot *slot; + struct vm_area_struct *vma; + struct rmap_item *rmap_item; + + if (list_empty(&ksm_mm_head.mm_list)) + return NULL; + + slot = ksm_scan.mm_slot; + if (slot == &ksm_mm_head) { + root_unstable_tree = RB_ROOT; + + spin_lock(&ksm_mmlist_lock); + slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list); + ksm_scan.mm_slot = slot; + spin_unlock(&ksm_mmlist_lock); +next_mm: + ksm_scan.address = 0; + ksm_scan.rmap_item = list_entry(&slot->rmap_list, + struct rmap_item, link); + } + + mm = slot->mm; + down_read(&mm->mmap_sem); + for (vma = find_vma(mm, ksm_scan.address); vma; vma = vma->vm_next) { + if (!(vma->vm_flags & VM_MERGEABLE)) + continue; + if (ksm_scan.address < vma->vm_start) + ksm_scan.address = vma->vm_start; + if (!vma->anon_vma) + ksm_scan.address = vma->vm_end; + + while (ksm_scan.address < vma->vm_end) { + *page = follow_page(vma, ksm_scan.address, FOLL_GET); + if (*page && PageAnon(*page)) { + flush_anon_page(vma, *page, ksm_scan.address); + flush_dcache_page(*page); + rmap_item = get_next_rmap_item(slot, + ksm_scan.rmap_item->link.next, + ksm_scan.address); + if (rmap_item) { + ksm_scan.rmap_item = rmap_item; + ksm_scan.address += PAGE_SIZE; + } else + put_page(*page); + up_read(&mm->mmap_sem); + return rmap_item; + } + if (*page) + put_page(*page); + ksm_scan.address += PAGE_SIZE; + cond_resched(); + } + } + + if (!ksm_scan.address) { + /* + * We've completed a full scan of all vmas, holding mmap_sem + * throughout, and found no VM_MERGEABLE: so do the same as + * __ksm_exit does to remove this mm from all our lists now. + */ + remove_mm_from_lists(mm); + up_read(&mm->mmap_sem); + slot = ksm_scan.mm_slot; + if (slot != &ksm_mm_head) + goto next_mm; + return NULL; + } + + /* + * Nuke all the rmap_items that are above this current rmap: + * because there were no VM_MERGEABLE vmas with such addresses. + */ + remove_trailing_rmap_items(slot, ksm_scan.rmap_item->link.next); + up_read(&mm->mmap_sem); + + spin_lock(&ksm_mmlist_lock); + slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list); + ksm_scan.mm_slot = slot; + spin_unlock(&ksm_mmlist_lock); + + /* Repeat until we've completed scanning the whole list */ + if (slot != &ksm_mm_head) + goto next_mm; + + /* + * Bump seqnr here rather than at top, so that __ksm_exit + * can skip rb_erase on unstable tree until we run again. + */ + ksm_scan.seqnr++; + return NULL; +} + +/** + * ksm_do_scan - the ksm scanner main worker function. + * @scan_npages - number of pages we want to scan before we return. + */ +static void ksm_do_scan(unsigned int scan_npages) +{ + struct rmap_item *rmap_item; + struct page *page; + + while (scan_npages--) { + cond_resched(); + rmap_item = scan_get_next_rmap_item(&page); + if (!rmap_item) + return; + if (!PageKsm(page) || !in_stable_tree(rmap_item)) + cmp_and_merge_page(page, rmap_item); + put_page(page); + } +} + +static int ksm_scan_thread(void *nothing) +{ + set_user_nice(current, 0); + + while (!kthread_should_stop()) { + if (ksm_run & KSM_RUN_MERGE) { + mutex_lock(&ksm_thread_mutex); + ksm_do_scan(ksm_thread_pages_to_scan); + mutex_unlock(&ksm_thread_mutex); + schedule_timeout_interruptible( + msecs_to_jiffies(ksm_thread_sleep_millisecs)); + } else { + wait_event_interruptible(ksm_thread_wait, + (ksm_run & KSM_RUN_MERGE) || + kthread_should_stop()); + } + } + return 0; +} + int ksm_madvise(struct vm_area_struct *vma, unsigned long start, unsigned long end, int advice, unsigned long *vm_flags) { @@ -33,7 +1307,8 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start, if (!(*vm_flags & VM_MERGEABLE)) return 0; /* just ignore the advice */ - /* Unmerge any merged pages here */ + if (vma->anon_vma) + unmerge_ksm_pages(vma, start, end); *vm_flags &= ~VM_MERGEABLE; break; @@ -44,13 +1319,217 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start, int __ksm_enter(struct mm_struct *mm) { - /* Allocate a structure to track mm and link it into KSM's list */ + struct mm_slot *mm_slot = alloc_mm_slot(); + if (!mm_slot) + return -ENOMEM; + + spin_lock(&ksm_mmlist_lock); + insert_to_mm_slots_hash(mm, mm_slot); + /* + * Insert just behind the scanning cursor, to let the area settle + * down a little; when fork is followed by immediate exec, we don't + * want ksmd to waste time setting up and tearing down an rmap_list. + */ + list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list); + spin_unlock(&ksm_mmlist_lock); + set_bit(MMF_VM_MERGEABLE, &mm->flags); return 0; } void __ksm_exit(struct mm_struct *mm) { - /* Unlink and free all KSM's structures which track this mm */ - clear_bit(MMF_VM_MERGEABLE, &mm->flags); + /* + * This process is exiting: doesn't hold and doesn't need mmap_sem; + * but we do need to exclude ksmd and other exiters while we modify + * the various lists and trees. + */ + mutex_lock(&ksm_thread_mutex); + remove_mm_from_lists(mm); + mutex_unlock(&ksm_thread_mutex); +} + +#define KSM_ATTR_RO(_name) \ + static struct kobj_attribute _name##_attr = __ATTR_RO(_name) +#define KSM_ATTR(_name) \ + static struct kobj_attribute _name##_attr = \ + __ATTR(_name, 0644, _name##_show, _name##_store) + +static ssize_t sleep_millisecs_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs); +} + +static ssize_t sleep_millisecs_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + unsigned long msecs; + int err; + + err = strict_strtoul(buf, 10, &msecs); + if (err || msecs > UINT_MAX) + return -EINVAL; + + ksm_thread_sleep_millisecs = msecs; + + return count; +} +KSM_ATTR(sleep_millisecs); + +static ssize_t pages_to_scan_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sprintf(buf, "%u\n", ksm_thread_pages_to_scan); +} + +static ssize_t pages_to_scan_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + int err; + unsigned long nr_pages; + + err = strict_strtoul(buf, 10, &nr_pages); + if (err || nr_pages > UINT_MAX) + return -EINVAL; + + ksm_thread_pages_to_scan = nr_pages; + + return count; +} +KSM_ATTR(pages_to_scan); + +static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr, + char *buf) +{ + return sprintf(buf, "%u\n", ksm_run); +} + +static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr, + const char *buf, size_t count) +{ + int err; + unsigned long flags; + + err = strict_strtoul(buf, 10, &flags); + if (err || flags > UINT_MAX) + return -EINVAL; + if (flags > KSM_RUN_UNMERGE) + return -EINVAL; + + /* + * KSM_RUN_MERGE sets ksmd running, and 0 stops it running. + * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items, + * breaking COW to free the kernel_pages_allocated (but leaves + * mm_slots on the list for when ksmd may be set running again). + */ + + mutex_lock(&ksm_thread_mutex); + if (ksm_run != flags) { + ksm_run = flags; + if (flags & KSM_RUN_UNMERGE) + unmerge_and_remove_all_rmap_items(); + } + mutex_unlock(&ksm_thread_mutex); + + if (flags & KSM_RUN_MERGE) + wake_up_interruptible(&ksm_thread_wait); + + return count; +} +KSM_ATTR(run); + +static ssize_t pages_shared_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sprintf(buf, "%lu\n", + ksm_pages_shared - ksm_kernel_pages_allocated); +} +KSM_ATTR_RO(pages_shared); + +static ssize_t kernel_pages_allocated_show(struct kobject *kobj, + struct kobj_attribute *attr, + char *buf) +{ + return sprintf(buf, "%lu\n", ksm_kernel_pages_allocated); +} +KSM_ATTR_RO(kernel_pages_allocated); + +static ssize_t max_kernel_pages_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + int err; + unsigned long nr_pages; + + err = strict_strtoul(buf, 10, &nr_pages); + if (err) + return -EINVAL; + + ksm_max_kernel_pages = nr_pages; + + return count; +} + +static ssize_t max_kernel_pages_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sprintf(buf, "%lu\n", ksm_max_kernel_pages); +} +KSM_ATTR(max_kernel_pages); + +static struct attribute *ksm_attrs[] = { + &sleep_millisecs_attr.attr, + &pages_to_scan_attr.attr, + &run_attr.attr, + &pages_shared_attr.attr, + &kernel_pages_allocated_attr.attr, + &max_kernel_pages_attr.attr, + NULL, +}; + +static struct attribute_group ksm_attr_group = { + .attrs = ksm_attrs, + .name = "ksm", +}; + +static int __init ksm_init(void) +{ + struct task_struct *ksm_thread; + int err; + + err = ksm_slab_init(); + if (err) + goto out; + + err = mm_slots_hash_init(); + if (err) + goto out_free1; + + ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd"); + if (IS_ERR(ksm_thread)) { + printk(KERN_ERR "ksm: creating kthread failed\n"); + err = PTR_ERR(ksm_thread); + goto out_free2; + } + + err = sysfs_create_group(mm_kobj, &ksm_attr_group); + if (err) { + printk(KERN_ERR "ksm: register sysfs failed\n"); + goto out_free3; + } + + return 0; + +out_free3: + kthread_stop(ksm_thread); +out_free2: + mm_slots_hash_free(); +out_free1: + ksm_slab_free(); +out: + return err; } +module_init(ksm_init) |