cregit-Linux how code gets into the kernel

Release 4.8 mm/ksm.c

Directory: mm
 * 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) 2008-2009 Red Hat, Inc.
 * Authors:
 *      Izik Eidus
 *      Andrea Arcangeli
 *      Chris Wright
 *      Hugh Dickins
 * 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/memory.h>
#include <linux/mmu_notifier.h>
#include <linux/swap.h>
#include <linux/ksm.h>
#include <linux/hashtable.h>
#include <linux/freezer.h>
#include <linux/oom.h>
#include <linux/numa.h>

#include <asm/tlbflush.h>
#include "internal.h"


#define NUMA(x)		(x)

#define DO_NUMA(x)	do { (x); } while (0)

#define NUMA(x)		(0)

#define DO_NUMA(x)	do { } while (0)

 * 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.)
 * If the merge_across_nodes tunable is unset, then KSM maintains multiple
 * stable trees and multiple unstable trees: one of each for each NUMA node.

 * 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 singly-linked 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 rmap_item *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_list: link to the next rmap to be scanned in 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_list;
unsigned long seqnr;

 * struct stable_node - node of the stable rbtree
 * @node: rb node of this ksm page in the stable tree
 * @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
 * @list: linked into migrate_nodes, pending placement in the proper node tree
 * @hlist: hlist head of rmap_items using this ksm page
 * @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid)
 * @nid: NUMA node id of stable tree in which linked (may not match kpfn)

struct stable_node {
	union {
struct rb_node node;	/* when node of stable tree */
		struct {		/* when listed for migration */
struct list_head *head;
struct list_head list;
struct hlist_head hlist;
unsigned long kpfn;
int nid;

 * struct rmap_item - reverse mapping item for virtual addresses
 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
 * @nid: NUMA node id of unstable tree in which linked (may not match page)
 * @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 the unstable tree
 * @head: pointer to stable_node heading this list in the stable tree
 * @hlist: link into hlist of rmap_items hanging off that stable_node

struct rmap_item {
struct rmap_item *rmap_list;
	union {
struct anon_vma *anon_vma;	/* when stable */
int nid;		/* when node of unstable tree */
struct mm_struct *mm;
unsigned long address;		/* + low bits used for flags below */
unsigned int oldchecksum;	/* when unstable */
	union {
struct rb_node node;	/* when node of unstable tree */
		struct {		/* when listed from stable tree */
struct stable_node *head;
struct hlist_node hlist;

#define SEQNR_MASK	0x0ff	
/* low bits of unstable tree seqnr */

#define UNSTABLE_FLAG	0x100	
/* is a node of the unstable tree */

#define STABLE_FLAG	0x200	
/* is listed from the stable tree */

/* The stable and unstable tree heads */

static struct rb_root one_stable_tree[1] = { RB_ROOT };

static struct rb_root one_unstable_tree[1] = { RB_ROOT };

static struct rb_root *root_stable_tree = one_stable_tree;

static struct rb_root *root_unstable_tree = one_unstable_tree;

/* Recently migrated nodes of stable tree, pending proper placement */
static LIST_HEAD(migrate_nodes);


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 *stable_node_cache;

static struct kmem_cache *mm_slot_cache;

/* The number of nodes in the stable tree */

static unsigned long ksm_pages_shared;

/* The number of page slots additionally sharing those nodes */

static unsigned long ksm_pages_sharing;

/* The number of nodes in the unstable tree */

static unsigned long ksm_pages_unshared;

/* The number of rmap_items in use: to calculate pages_volatile */

static unsigned long ksm_rmap_items;

/* Number of pages ksmd should scan in one batch */

static unsigned int ksm_thread_pages_to_scan = 100;

/* Milliseconds ksmd should sleep between batches */

static unsigned int ksm_thread_sleep_millisecs = 20;

/* Zeroed when merging across nodes is not allowed */

static unsigned int ksm_merge_across_nodes = 1;

static int ksm_nr_node_ids = 1;

#define ksm_merge_across_nodes	1U

#define ksm_nr_node_ids		1

#define KSM_RUN_STOP	0

#define KSM_RUN_MERGE	1



static unsigned long ksm_run = KSM_RUN_STOP;
static void wait_while_offlining(void);

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; stable_node_cache = KSM_KMEM_CACHE(stable_node, 0); if (!stable_node_cache) goto out_free1; mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0); if (!mm_slot_cache) goto out_free2; return 0; out_free2: kmem_cache_destroy(stable_node_cache); out_free1: kmem_cache_destroy(rmap_item_cache); out: return -ENOMEM; }


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static void __init ksm_slab_free(void) { kmem_cache_destroy(mm_slot_cache); kmem_cache_destroy(stable_node_cache); kmem_cache_destroy(rmap_item_cache); mm_slot_cache = NULL; }


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static inline struct rmap_item *alloc_rmap_item(void) { struct rmap_item *rmap_item; rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN); if (rmap_item) ksm_rmap_items++; return rmap_item; }


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static inline void free_rmap_item(struct rmap_item *rmap_item) { ksm_rmap_items--; rmap_item->mm = NULL; /* debug safety */ kmem_cache_free(rmap_item_cache, rmap_item); }


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static inline struct stable_node *alloc_stable_node(void) { return kmem_cache_alloc(stable_node_cache, GFP_KERNEL); }


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static inline void free_stable_node(struct stable_node *stable_node) { kmem_cache_free(stable_node_cache, stable_node); }


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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); }


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static inline void free_mm_slot(struct mm_slot *mm_slot) { kmem_cache_free(mm_slot_cache, mm_slot); }


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static struct mm_slot *get_mm_slot(struct mm_struct *mm) { struct mm_slot *slot; hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm) if (slot->mm == mm) return slot; return NULL; }


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static void insert_to_mm_slots_hash(struct mm_struct *mm, struct mm_slot *mm_slot) { mm_slot->mm = mm; hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm); }


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/* * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's * page tables after it has passed through ksm_exit() - which, if necessary, * takes mmap_sem briefly to serialize against them. ksm_exit() does not set * a special flag: they can just back out as soon as mm_users goes to zero. * ksm_test_exit() is used throughout to make this test for exit: in some * places for correctness, in some places just to avoid unnecessary work. */
static inline bool ksm_test_exit(struct mm_struct *mm) { return atomic_read(&mm->mm_users) == 0; }


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/* * We use break_ksm to break COW on a ksm page: it's a stripped down * * if (get_user_pages(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. * * FAULT_FLAG/FOLL_REMOTE are because we do this outside the context * of the process that owns 'vma'. We also do not want to enforce * protection keys here anyway. */
static int break_ksm(struct vm_area_struct *vma, unsigned long addr) { struct page *page; int ret = 0; do { cond_resched(); page = follow_page(vma, addr, FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE); if (IS_ERR_OR_NULL(page)) break; if (PageKsm(page)) ret = handle_mm_fault(vma, addr, FAULT_FLAG_WRITE | FAULT_FLAG_REMOTE); else ret = VM_FAULT_WRITE; put_page(page); } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM))); /* * We must loop because handle_mm_fault() may back out if there's * any difficulty e.g. if pte accessed bit gets updated concurrently. * * VM_FAULT_WRITE is what we have been hoping for: it indicates that * COW has been broken, even if the vma does not permit VM_WRITE; * but note that a concurrent fault might break PageKsm for us. * * VM_FAULT_SIGBUS could occur if we race with truncation of the * backing file, which also invalidates anonymous pages: that's * okay, that truncation will have unmapped the PageKsm for us. * * VM_FAULT_OOM: at the time of writing (late July 2009), setting * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the * current task has TIF_MEMDIE set, and will be OOM killed on return * to user; and ksmd, having no mm, would never be chosen for that. * * But if the mm is in a limited mem_cgroup, then the fault may fail * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and * even ksmd can fail in this way - though it's usually breaking ksm * just to undo a merge it made a moment before, so unlikely to oom. * * That's a pity: we might therefore have more kernel pages allocated * than we're counting as nodes in the stable tree; but ksm_do_scan * will retry to break_cow on each pass, so should recover the page * in due course. The important thing is to not let VM_MERGEABLE * be cleared while any such pages might remain in the area. */ return (ret & VM_FAULT_OOM) ? -ENOMEM : 0; }


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static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm, unsigned long addr) { struct vm_area_struct *vma; if (ksm_test_exit(mm)) return NULL; vma = find_vma(mm, addr); if (!vma || vma->vm_start > addr) return NULL; if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) return NULL; return vma; }


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static void break_cow(struct rmap_item *rmap_item) { struct mm_struct *mm = rmap_item->mm; unsigned long addr = rmap_item->address; struct vm_area_struct *vma; /* * It is not an accident that whenever we want to break COW * to undo, we also need to drop a reference to the anon_vma. */ put_anon_vma(rmap_item->anon_vma); down_read(&mm->mmap_sem); vma = find_mergeable_vma(mm, addr); if (vma) break_ksm(vma, addr); up_read(&mm->mmap_sem); }


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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_mergeable_vma(mm, addr); if (!vma) goto out; page = follow_page(vma, addr, FOLL_GET); if (IS_ERR_OR_NULL(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; }


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/* * This helper is used for getting right index into array of tree roots. * When merge_across_nodes knob is set to 1, there are only two rb-trees for * stable and unstable pages from all nodes with roots in index 0. Otherwise, * every node has its own stable and unstable tree. */
static inline int get_kpfn_nid(unsigned long kpfn) { return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn)); }


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static void remove_node_from_stable_tree(struct stable_node *stable_node) { struct rmap_item *rmap_item; hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) { if (rmap_item-> ksm_pages_sharing--; else ksm_pages_shared--; put_anon_vma(rmap_item->anon_vma); rmap_item->address &= PAGE_MASK; cond_resched(); } if (stable_node->head == &migrate_nodes) list_del(&stable_node->list); else rb_erase(&stable_node->node, root_stable_tree + NUMA(stable_node->nid)); free_stable_node(stable_node); }


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/* * get_ksm_page: checks if the page indicated by the stable node * is still its ksm page, despite having held no reference to it. * In which case we can trust the content of the page, and it * returns the gotten page; but if the page has now been zapped, * remove the stale node from the stable tree and return NULL. * But beware, the stable node's page might be being migrated. * * You would expect the stable_node to hold a reference to the ksm page. * But if it increments the page's count, swapping out has to wait for * ksmd to come around again before it can free the page, which may take * seconds or even minutes: much too unresponsive. So instead we use a * "keyhole reference": access to the ksm page from the stable node peeps * out through its keyhole to see if that page still holds the right key, * pointing back to this stable node. This relies on freeing a PageAnon * page to reset its page->mapping to NULL, and relies on no other use of * a page to put something that might look like our key in page->mapping. * is on its way to being freed; but it is an anomaly to bear in mind. */
static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it) { struct page *page; void *expected_mapping; unsigned long kpfn; expected_mapping = (void *)((unsigned long)stable_node | PAGE_MAPPING_KSM); again: kpfn = READ_ONCE(stable_node->kpfn); page = pfn_to_page(kpfn); /* * page is computed from kpfn, so on most architectures reading * page->mapping is naturally ordered after reading node->kpfn, * but on Alpha we need to be more careful. */ smp_read_barrier_depends(); if (READ_ONCE(page->mapping) != expected_mapping) goto stale; /* * We cannot do anything with the page while its refcount is 0. * Usually 0 means free, or tail of a higher-order page: in which * case this node is no longer referenced, and should be freed; * however, it might mean that the page is under page_freeze_refs(). * The __remove_mapping() case is easy, again the node is now stale; * but if page is swapcache in migrate_page_move_mapping(), it might * still be our page, in which case it's essential to keep the node. */ while (!get_page_unless_zero(page)) { /* * Another check for page->mapping != expected_mapping would * work here too. We have chosen the !PageSwapCache test to * optimize the common case, when the page is or is about to * be freed: PageSwapCache is cleared (under spin_lock_irq) * in the freeze_refs section of __remove_mapping(); but Anon * page->mapping reset to NULL later, in free_pages_prepare(). */ if (!PageSwapCache(page)) goto stale; cpu_relax(); } if (READ_ONCE(page->mapping) != expected_mapping) { put_page(page); goto stale; } if (lock_it) { lock_page(page); if (READ_ONCE(page->mapping) != expected_mapping) { unlock_page(page); put_page(page); goto stale; } } return page; stale: /* * We come here from above when page->mapping or !PageSwapCache * suggests that the node is stale; but it might be under migration. * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(), * before checking whether node->kpfn has been changed. */ smp_rmb(); if (READ_ONCE(stable_node->kpfn) != kpfn) goto again; remove_node_from_stable_tree(stable_node); return NULL; }


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/* * 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 (rmap_item->address & STABLE_FLAG) { struct stable_node *stable_node; struct page *page; stable_node = rmap_item->head; page = get_ksm_page(stable_node, true); if (!page) goto out; hlist_del(&rmap_item->hlist); unlock_page(page); put_page(page); if (!hlist_empty(&stable_node->hlist)) ksm_pages_sharing--; else ksm_pages_shared--; put_anon_vma(rmap_item->anon_vma); rmap_item->address &= PAGE_MASK; } else if (rmap_item->address & UNSTABLE_FLAG) { unsigned char age; /* * Usually ksmd can and must skip the rb_erase, because * root_unstable_tree was already reset to RB_ROOT. * But be careful when an mm is exiting: do the rb_erase * if this rmap_item was inserted by this scan, rather * than left over from before. */ age = (unsigned char)(ksm_scan.seqnr - rmap_item->address); BUG_ON(age > 1); if (!age) rb_erase(&rmap_item->node, root_unstable_tree + NUMA(rmap_item->nid)); ksm_pages_unshared--; rmap_item->address &= PAGE_MASK; } out: cond_resched(); /* we're called from many long loops */ }


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static void remove_trailing_rmap_items(struct mm_slot *mm_slot, struct rmap_item **rmap_list) { while (*rmap_list) { struct rmap_item *rmap_item = *rmap_list; *rmap_list = rmap_item->rmap_list; remove_rmap_item_from_tree(rmap_item); free_rmap_item(rmap_item); } }


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/* * Though it's very tempting to unmerge rmap_items from stable tree 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). * * Similarly, although we'd like to remove rmap_items (so updating counts * and freeing memory) when unmerging an area, it's easier to leave that * to the next pass of ksmd - consider, for example, how ksmd might be * in cmp_and_merge_page on one of the rmap_items we would be removing. */
static int unmerge_ksm_pages(struct vm_area_struct *vma, unsigned long start, unsigned long end) { unsigned long addr; int err = 0; for (addr = start; addr < end && !err; addr += PAGE_SIZE) { if (ksm_test_exit(vma->vm_mm)) break; if (signal_pending(current)) err = -ERESTARTSYS; else err = break_ksm(vma, addr); } return err; }


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#ifdef CONFIG_SYSFS /* * Only called through the sysfs control interface: */
static int remove_stable_node(struct stable_node *stable_node) { struct page *page; int err; page = get_ksm_page(stable_node, true); if (!page) { /* * get_ksm_page did remove_node_from_stable_tree itself. */ return 0; } if (WARN_ON_ONCE(page_mapped(page))) { /* * This should not happen: but if it does, just refuse to let * merge_across_nodes be switched - there is no need to panic. */ err = -EBUSY; } else { /* * The stable node did not yet appear stale to get_ksm_page(), * since that allows for an unmapped ksm page to be recognized * right up until it is freed; but the node is safe to remove. * This page might be in a pagevec waiting to be freed, * or it might be PageSwapCache (perhaps under writeback), * or it might have been removed from swapcache a moment ago. */ set_page_stable_node(page, NULL); remove_node_from_stable_tree(stable_node); err = 0; } unlock_page(page); put_page(page); return err; }


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static int remove_all_stable_nodes(void) { struct stable_node *stable_node, *next; int nid; int err = 0; for (nid = 0; nid < ksm_nr_node_ids; nid++) { while (root_stable_tree[nid].rb_node) { stable_node = rb_entry(root_stable_tree[nid].rb_node, struct stable_node, node); if (remove_stable_node(stable_node)) { err = -EBUSY; break; /* proceed to next nid */ } cond_resched(); } } list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) { if (remove_stable_node(stable_node)) err = -EBUSY; cond_resched(); } return err; }


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static int unmerge_and_remove_all_rmap_items(void) { struct mm_slot *mm_slot; struct mm_struct *mm; struct vm_area_struct *vma; int err = 0; spin_lock(&ksm_mmlist_lock); ksm_scan.mm_slot = list_entry(, struct mm_slot, mm_list); spin_unlock(&ksm_mmlist_lock); for (mm_slot = ksm_scan.mm_slot; mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) { mm = mm_slot->mm; down_read(&mm->mmap_sem); for (vma = mm->mmap; vma; vma = vma->vm_next) { if (ksm_test_exit(mm)) break; if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) continue; err = unmerge_ksm_pages(vma, vma->vm_start, vma->vm_end); if (err) goto error; } remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list); up_read(&mm->mmap_sem); spin_lock(&ksm_mmlist_lock); ksm_scan.mm_slot = list_entry(mm_slot->, struct mm_slot, mm_list); if (ksm_test_exit(mm)) { hash_del(&mm_slot->link); list_del(&mm_slot->mm_list); spin_unlock(&ksm_mmlist_lock); free_mm_slot(mm_slot); clear_bit(MMF_VM_MERGEABLE, &mm->flags); mmdrop(mm); } else spin_unlock(&ksm_mmlist_lock); } /* Clean up stable nodes, but don't worry if some are still busy */ remove_all_stable_nodes(); ksm_scan.seqnr = 0; return 0; error: up_read(&mm->mmap_sem); spin_lock(&ksm_mmlist_lock); ksm_scan.mm_slot = &ksm_mm_head; spin_unlock(&ksm_mmlist_lock); return err; }


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#endif /* CONFIG_SYSFS */
static u32 calc_checksum(struct page *page) { u32 checksum; void *addr = kmap_atomic(page); checksum = jhash2(addr, PAGE_SIZE / 4, 17); kunmap_atomic(addr); return checksum; }


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static int memcmp_pages(struct page *page1, struct page *page2) { char *addr1, *addr2; int ret; addr1 = kmap_atomic(page1); addr2 = kmap_atomic(page2); ret = memcmp(addr1, addr2, PAGE_SIZE); kunmap_atomic(addr2); kunmap_atomic(addr1); return ret; }


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static inline int pages_identical(struct page *page1, struct page *page2) { return !memcmp_pages(page1, page2); }


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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; unsigned long mmun_start; /* For mmu_notifiers */ unsigned long mmun_end; /* For mmu_notifiers */ addr = page_address_in_vma(page, vma); if (addr == -EFAULT) goto out; BUG_ON(PageTransCompound(page)); mmun_start = addr; mmun_end = addr + PAGE_SIZE; mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end); ptep = page_check_address(page, mm, addr, &ptl, 0); if (!ptep) goto out_mn; if (pte_write(*ptep) || pte_dirty(*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 doesn't * 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_notify(vma, addr, ptep); /* * Check that no O_DIRECT or similar I/O is in progress on the * page */ if (page_mapcount(page) + 1 + swapped != page_count(page)) { set_pte_at(mm, addr, ptep, entry); goto out_unlock; } if (pte_dirty(entry)) set_page_dirty(page); entry = pte_mkclean(pte_wrprotect(entry)); set_pte_at_notify(mm, addr, ptep, entry); } *orig_pte = *ptep; err = 0; out_unlock: pte_unmap_unlock(ptep, ptl); out_mn: mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end); out: return err; }


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robin holtrobin holt10.36%112.50%

/** * replace_page - replace page in vma by new ksm page * @vma: vma that holds the pte pointing to page * @page: the page we are replacing by kpage * @kpage: the ksm page we replace page 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 *page, struct page *kpage, pte_t orig_pte) { struct mm_struct *mm = vma->vm_mm; pmd_t *pmd; pte_t *ptep; spinlock_t *ptl; unsigned long addr; int err = -EFAULT; unsigned long mmun_start; /* For mmu_notifiers */ unsigned long mmun_end; /* For mmu_notifiers */ addr = page_address_in_vma(page, vma); if (addr == -EFAULT) goto out; pmd = mm_find_pmd(mm, addr); if (!pmd) goto out; mmun_start =