* 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 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
+ * @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 {
- struct rb_node 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;
+#ifdef CONFIG_NUMA
+ int nid;
+#endif
};
/**
* 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
- * @nid: NUMA node id of unstable tree in which linked (may not match page)
* @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;
- struct anon_vma *anon_vma; /* when stable */
+ union {
+ struct anon_vma *anon_vma; /* when stable */
+#ifdef CONFIG_NUMA
+ int nid; /* when node of unstable tree */
+#endif
+ };
struct mm_struct *mm;
unsigned long address; /* + low bits used for flags below */
unsigned int oldchecksum; /* when unstable */
-#ifdef CONFIG_NUMA
- int nid;
-#endif
union {
struct rb_node node; /* when node of unstable tree */
struct { /* when listed from stable tree */
#define STABLE_FLAG 0x200 /* is listed from the stable tree */
/* The stable and unstable tree heads */
-static struct rb_root root_unstable_tree[MAX_NUMNODES];
-static struct rb_root root_stable_tree[MAX_NUMNODES];
+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);
#define MM_SLOTS_HASH_BITS 10
static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
#ifdef CONFIG_NUMA
/* Zeroed when merging across nodes is not allowed */
static unsigned int ksm_merge_across_nodes = 1;
+static int ksm_nr_node_ids = 1;
#else
#define ksm_merge_across_nodes 1U
+#define ksm_nr_node_ids 1
#endif
#define KSM_RUN_STOP 0
#define KSM_RUN_MERGE 1
#define KSM_RUN_UNMERGE 2
-static unsigned int ksm_run = KSM_RUN_STOP;
+#define KSM_RUN_OFFLINE 4
+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 struct mm_slot *get_mm_slot(struct mm_struct *mm)
{
- struct hlist_node *node;
struct mm_slot *slot;
- hash_for_each_possible(mm_slots_hash, slot, node, link, (unsigned long)mm)
+ hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm)
if (slot->mm == mm)
return slot;
hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm);
}
-static inline int in_stable_tree(struct rmap_item *rmap_item)
-{
- return rmap_item->address & STABLE_FLAG;
-}
-
/*
* 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,
do {
cond_resched();
- page = follow_page(vma, addr, FOLL_GET);
+ page = follow_page(vma, addr, FOLL_GET | FOLL_MIGRATION);
if (IS_ERR_OR_NULL(page))
break;
if (PageKsm(page))
static void remove_node_from_stable_tree(struct stable_node *stable_node)
{
struct rmap_item *rmap_item;
- struct hlist_node *hlist;
- int nid;
- hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
+ hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
if (rmap_item->hlist.next)
ksm_pages_sharing--;
else
cond_resched();
}
- nid = get_kpfn_nid(stable_node->kpfn);
- rb_erase(&stable_node->node, &root_stable_tree[nid]);
+ 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);
}
* 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
* 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.
- *
- * include/linux/pagemap.h page_cache_get_speculative() is a good reference,
- * but this is different - made simpler by ksm_thread_mutex being held, but
- * interesting for assuming that no other use of the struct page could ever
- * put our expected_mapping into page->mapping (or a field of the union which
- * coincides with page->mapping). The RCU calls are not for KSM at all, but
- * to keep the page_count protocol described with page_cache_get_speculative.
- *
- * Note: it is possible that get_ksm_page() will return NULL one moment,
- * then page the next, if the page is in between page_freeze_refs() and
- * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
* 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)
+static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it)
{
struct page *page;
void *expected_mapping;
+ unsigned long kpfn;
- page = pfn_to_page(stable_node->kpfn);
expected_mapping = (void *)stable_node +
(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
- rcu_read_lock();
- if (page->mapping != expected_mapping)
- goto stale;
- if (!get_page_unless_zero(page))
+again:
+ kpfn = ACCESS_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 (ACCESS_ONCE(page->mapping) != expected_mapping)
goto stale;
- if (page->mapping != expected_mapping) {
+
+ /*
+ * 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 (ACCESS_ONCE(page->mapping) != expected_mapping) {
put_page(page);
goto stale;
}
- rcu_read_unlock();
+
+ if (lock_it) {
+ lock_page(page);
+ if (ACCESS_ONCE(page->mapping) != expected_mapping) {
+ unlock_page(page);
+ put_page(page);
+ goto stale;
+ }
+ }
return page;
+
stale:
- rcu_read_unlock();
+ /*
+ * 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 (ACCESS_ONCE(stable_node->kpfn) != kpfn)
+ goto again;
remove_node_from_stable_tree(stable_node);
return NULL;
}
struct page *page;
stable_node = rmap_item->head;
- page = get_ksm_page(stable_node);
+ page = get_ksm_page(stable_node, true);
if (!page)
goto out;
- lock_page(page);
hlist_del(&rmap_item->hlist);
unlock_page(page);
put_page(page);
BUG_ON(age > 1);
if (!age)
rb_erase(&rmap_item->node,
- &root_unstable_tree[NUMA(rmap_item->nid)]);
+ root_unstable_tree + NUMA(rmap_item->nid));
ksm_pages_unshared--;
rmap_item->address &= PAGE_MASK;
}
/*
* 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;
+}
+
+static int remove_all_stable_nodes(void)
+{
+ struct stable_node *stable_node;
+ struct list_head *this, *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_safe(this, next, &migrate_nodes) {
+ stable_node = list_entry(this, struct stable_node, list);
+ if (remove_stable_node(stable_node))
+ err = -EBUSY;
+ cond_resched();
+ }
+ return err;
+}
+
static int unmerge_and_remove_all_rmap_items(void)
{
struct mm_slot *mm_slot;
}
}
+ /* Clean up stable nodes, but don't worry if some are still busy */
+ remove_all_stable_nodes();
ksm_scan.seqnr = 0;
return 0;
if (err)
goto out;
+ /* Unstable nid is in union with stable anon_vma: remove first */
+ remove_rmap_item_from_tree(rmap_item);
+
/* Must get reference to anon_vma while still holding mmap_sem */
rmap_item->anon_vma = vma->anon_vma;
get_anon_vma(vma->anon_vma);
*/
static struct page *stable_tree_search(struct page *page)
{
- struct rb_node *node;
- struct stable_node *stable_node;
int nid;
+ struct rb_root *root;
+ struct rb_node **new;
+ struct rb_node *parent;
+ struct stable_node *stable_node;
+ struct stable_node *page_node;
- stable_node = page_stable_node(page);
- if (stable_node) { /* ksm page forked */
+ page_node = page_stable_node(page);
+ if (page_node && page_node->head != &migrate_nodes) {
+ /* ksm page forked */
get_page(page);
return page;
}
nid = get_kpfn_nid(page_to_pfn(page));
- node = root_stable_tree[nid].rb_node;
+ root = root_stable_tree + nid;
+again:
+ new = &root->rb_node;
+ parent = NULL;
- while (node) {
+ while (*new) {
struct page *tree_page;
int ret;
cond_resched();
- stable_node = rb_entry(node, struct stable_node, node);
- tree_page = get_ksm_page(stable_node);
+ stable_node = rb_entry(*new, struct stable_node, node);
+ tree_page = get_ksm_page(stable_node, false);
if (!tree_page)
return NULL;
ret = memcmp_pages(page, tree_page);
+ put_page(tree_page);
- if (ret < 0) {
- put_page(tree_page);
- node = node->rb_left;
- } else if (ret > 0) {
- put_page(tree_page);
- node = node->rb_right;
- } else
- return tree_page;
+ parent = *new;
+ if (ret < 0)
+ new = &parent->rb_left;
+ else if (ret > 0)
+ new = &parent->rb_right;
+ else {
+ /*
+ * Lock and unlock the stable_node's page (which
+ * might already have been migrated) so that page
+ * migration is sure to notice its raised count.
+ * It would be more elegant to return stable_node
+ * than kpage, but that involves more changes.
+ */
+ tree_page = get_ksm_page(stable_node, true);
+ if (tree_page) {
+ unlock_page(tree_page);
+ if (get_kpfn_nid(stable_node->kpfn) !=
+ NUMA(stable_node->nid)) {
+ put_page(tree_page);
+ goto replace;
+ }
+ return tree_page;
+ }
+ /*
+ * There is now a place for page_node, but the tree may
+ * have been rebalanced, so re-evaluate parent and new.
+ */
+ if (page_node)
+ goto again;
+ return NULL;
+ }
}
- return NULL;
+ if (!page_node)
+ return NULL;
+
+ list_del(&page_node->list);
+ DO_NUMA(page_node->nid = nid);
+ rb_link_node(&page_node->node, parent, new);
+ rb_insert_color(&page_node->node, root);
+ get_page(page);
+ return page;
+
+replace:
+ if (page_node) {
+ list_del(&page_node->list);
+ DO_NUMA(page_node->nid = nid);
+ rb_replace_node(&stable_node->node, &page_node->node, root);
+ get_page(page);
+ } else {
+ rb_erase(&stable_node->node, root);
+ page = NULL;
+ }
+ stable_node->head = &migrate_nodes;
+ list_add(&stable_node->list, stable_node->head);
+ return page;
}
/*
{
int nid;
unsigned long kpfn;
+ struct rb_root *root;
struct rb_node **new;
struct rb_node *parent = NULL;
struct stable_node *stable_node;
kpfn = page_to_pfn(kpage);
nid = get_kpfn_nid(kpfn);
- new = &root_stable_tree[nid].rb_node;
+ root = root_stable_tree + nid;
+ new = &root->rb_node;
while (*new) {
struct page *tree_page;
cond_resched();
stable_node = rb_entry(*new, struct stable_node, node);
- tree_page = get_ksm_page(stable_node);
+ tree_page = get_ksm_page(stable_node, false);
if (!tree_page)
return NULL;
INIT_HLIST_HEAD(&stable_node->hlist);
stable_node->kpfn = kpfn;
set_page_stable_node(kpage, stable_node);
+ DO_NUMA(stable_node->nid = nid);
rb_link_node(&stable_node->node, parent, new);
- rb_insert_color(&stable_node->node, &root_stable_tree[nid]);
+ rb_insert_color(&stable_node->node, root);
return stable_node;
}
int nid;
nid = get_kpfn_nid(page_to_pfn(page));
- root = &root_unstable_tree[nid];
+ root = root_unstable_tree + nid;
new = &root->rb_node;
while (*new) {
return NULL;
}
- /*
- * If tree_page has been migrated to another NUMA node, it
- * will be flushed out and put into the right unstable tree
- * next time: only merge with it if merge_across_nodes.
- */
- if (!ksm_merge_across_nodes && page_to_nid(tree_page) != nid) {
- put_page(tree_page);
- return NULL;
- }
-
ret = memcmp_pages(page, tree_page);
parent = *new;
} else if (ret > 0) {
put_page(tree_page);
new = &parent->rb_right;
+ } else if (!ksm_merge_across_nodes &&
+ page_to_nid(tree_page) != nid) {
+ /*
+ * If tree_page has been migrated to another NUMA node,
+ * it will be flushed out and put in the right unstable
+ * tree next time: only merge with it when across_nodes.
+ */
+ put_page(tree_page);
+ return NULL;
} else {
*tree_pagep = tree_page;
return tree_rmap_item;
static void stable_tree_append(struct rmap_item *rmap_item,
struct stable_node *stable_node)
{
- /*
- * Usually rmap_item->nid is already set correctly,
- * but it may be wrong after switching merge_across_nodes.
- */
- DO_NUMA(rmap_item->nid = get_kpfn_nid(stable_node->kpfn));
rmap_item->head = stable_node;
rmap_item->address |= STABLE_FLAG;
hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
unsigned int checksum;
int err;
- remove_rmap_item_from_tree(rmap_item);
+ stable_node = page_stable_node(page);
+ if (stable_node) {
+ if (stable_node->head != &migrate_nodes &&
+ get_kpfn_nid(stable_node->kpfn) != NUMA(stable_node->nid)) {
+ rb_erase(&stable_node->node,
+ root_stable_tree + NUMA(stable_node->nid));
+ stable_node->head = &migrate_nodes;
+ list_add(&stable_node->list, stable_node->head);
+ }
+ if (stable_node->head != &migrate_nodes &&
+ rmap_item->head == stable_node)
+ return;
+ }
/* We first start with searching the page inside the stable tree */
kpage = stable_tree_search(page);
+ if (kpage == page && rmap_item->head == stable_node) {
+ put_page(kpage);
+ return;
+ }
+
+ remove_rmap_item_from_tree(rmap_item);
+
if (kpage) {
err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
if (!err) {
kpage = try_to_merge_two_pages(rmap_item, page,
tree_rmap_item, tree_page);
put_page(tree_page);
- /*
- * 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 (kpage) {
- remove_rmap_item_from_tree(tree_rmap_item);
-
+ /*
+ * The pages were successfully merged: insert new
+ * node in the stable tree and add both rmap_items.
+ */
lock_page(kpage);
stable_node = stable_tree_insert(kpage);
if (stable_node) {
*/
lru_add_drain_all();
- for (nid = 0; nid < nr_node_ids; nid++)
+ /*
+ * Whereas stale stable_nodes on the stable_tree itself
+ * get pruned in the regular course of stable_tree_search(),
+ * those moved out to the migrate_nodes list can accumulate:
+ * so prune them once before each full scan.
+ */
+ if (!ksm_merge_across_nodes) {
+ struct stable_node *stable_node;
+ struct list_head *this, *next;
+ struct page *page;
+
+ list_for_each_safe(this, next, &migrate_nodes) {
+ stable_node = list_entry(this,
+ struct stable_node, list);
+ page = get_ksm_page(stable_node, false);
+ if (page)
+ put_page(page);
+ cond_resched();
+ }
+ }
+
+ for (nid = 0; nid < ksm_nr_node_ids; nid++)
root_unstable_tree[nid] = RB_ROOT;
spin_lock(&ksm_mmlist_lock);
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);
+ cmp_and_merge_page(page, rmap_item);
put_page(page);
}
}
while (!kthread_should_stop()) {
mutex_lock(&ksm_thread_mutex);
+ wait_while_offlining();
if (ksmd_should_run())
ksm_do_scan(ksm_thread_pages_to_scan);
mutex_unlock(&ksm_thread_mutex);
spin_lock(&ksm_mmlist_lock);
insert_to_mm_slots_hash(mm, mm_slot);
/*
- * Insert just behind the scanning cursor, to let the area settle
+ * When KSM_RUN_MERGE (or KSM_RUN_STOP),
+ * 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.
+ *
+ * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
+ * scanning cursor, otherwise KSM pages in newly forked mms will be
+ * missed: then we might as well insert at the end of the list.
*/
- list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
+ if (ksm_run & KSM_RUN_UNMERGE)
+ list_add_tail(&mm_slot->mm_list, &ksm_mm_head.mm_list);
+ else
+ 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);
}
}
-struct page *ksm_does_need_to_copy(struct page *page,
+struct page *ksm_might_need_to_copy(struct page *page,
struct vm_area_struct *vma, unsigned long address)
{
+ struct anon_vma *anon_vma = page_anon_vma(page);
struct page *new_page;
+ if (PageKsm(page)) {
+ if (page_stable_node(page) &&
+ !(ksm_run & KSM_RUN_UNMERGE))
+ return page; /* no need to copy it */
+ } else if (!anon_vma) {
+ return page; /* no need to copy it */
+ } else if (anon_vma->root == vma->anon_vma->root &&
+ page->index == linear_page_index(vma, address)) {
+ return page; /* still no need to copy it */
+ }
+ if (!PageUptodate(page))
+ return page; /* let do_swap_page report the error */
+
new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
if (new_page) {
copy_user_highpage(new_page, page, address, vma);
{
struct stable_node *stable_node;
struct rmap_item *rmap_item;
- struct hlist_node *hlist;
unsigned int mapcount = page_mapcount(page);
int referenced = 0;
int search_new_forks = 0;
if (!stable_node)
return 0;
again:
- hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
+ hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
struct anon_vma *anon_vma = rmap_item->anon_vma;
struct anon_vma_chain *vmac;
struct vm_area_struct *vma;
int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
{
struct stable_node *stable_node;
- struct hlist_node *hlist;
struct rmap_item *rmap_item;
int ret = SWAP_AGAIN;
int search_new_forks = 0;
if (!stable_node)
return SWAP_FAIL;
again:
- hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
+ hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
struct anon_vma *anon_vma = rmap_item->anon_vma;
struct anon_vma_chain *vmac;
struct vm_area_struct *vma;
struct vm_area_struct *, unsigned long, void *), void *arg)
{
struct stable_node *stable_node;
- struct hlist_node *hlist;
struct rmap_item *rmap_item;
int ret = SWAP_AGAIN;
int search_new_forks = 0;
if (!stable_node)
return ret;
again:
- hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
+ hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
struct anon_vma *anon_vma = rmap_item->anon_vma;
struct anon_vma_chain *vmac;
struct vm_area_struct *vma;
if (stable_node) {
VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
stable_node->kpfn = page_to_pfn(newpage);
+ /*
+ * newpage->mapping was set in advance; now we need smp_wmb()
+ * to make sure that the new stable_node->kpfn is visible
+ * to get_ksm_page() before it can see that oldpage->mapping
+ * has gone stale (or that PageSwapCache has been cleared).
+ */
+ smp_wmb();
+ set_page_stable_node(oldpage, NULL);
}
}
#endif /* CONFIG_MIGRATION */
#ifdef CONFIG_MEMORY_HOTREMOVE
-static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
- unsigned long end_pfn)
+static int just_wait(void *word)
+{
+ schedule();
+ return 0;
+}
+
+static void wait_while_offlining(void)
+{
+ while (ksm_run & KSM_RUN_OFFLINE) {
+ mutex_unlock(&ksm_thread_mutex);
+ wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
+ just_wait, TASK_UNINTERRUPTIBLE);
+ mutex_lock(&ksm_thread_mutex);
+ }
+}
+
+static void ksm_check_stable_tree(unsigned long start_pfn,
+ unsigned long end_pfn)
{
+ struct stable_node *stable_node;
+ struct list_head *this, *next;
struct rb_node *node;
int nid;
- for (nid = 0; nid < nr_node_ids; nid++)
- for (node = rb_first(&root_stable_tree[nid]); node;
- node = rb_next(node)) {
- struct stable_node *stable_node;
-
+ for (nid = 0; nid < ksm_nr_node_ids; nid++) {
+ node = rb_first(root_stable_tree + nid);
+ while (node) {
stable_node = rb_entry(node, struct stable_node, node);
if (stable_node->kpfn >= start_pfn &&
- stable_node->kpfn < end_pfn)
- return stable_node;
+ stable_node->kpfn < end_pfn) {
+ /*
+ * Don't get_ksm_page, page has already gone:
+ * which is why we keep kpfn instead of page*
+ */
+ remove_node_from_stable_tree(stable_node);
+ node = rb_first(root_stable_tree + nid);
+ } else
+ node = rb_next(node);
+ cond_resched();
}
-
- return NULL;
+ }
+ list_for_each_safe(this, next, &migrate_nodes) {
+ stable_node = list_entry(this, struct stable_node, list);
+ if (stable_node->kpfn >= start_pfn &&
+ stable_node->kpfn < end_pfn)
+ remove_node_from_stable_tree(stable_node);
+ cond_resched();
+ }
}
static int ksm_memory_callback(struct notifier_block *self,
unsigned long action, void *arg)
{
struct memory_notify *mn = arg;
- struct stable_node *stable_node;
switch (action) {
case MEM_GOING_OFFLINE:
/*
- * Keep it very simple for now: just lock out ksmd and
- * MADV_UNMERGEABLE while any memory is going offline.
- * mutex_lock_nested() is necessary because lockdep was alarmed
- * that here we take ksm_thread_mutex inside notifier chain
- * mutex, and later take notifier chain mutex inside
- * ksm_thread_mutex to unlock it. But that's safe because both
- * are inside mem_hotplug_mutex.
+ * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
+ * and remove_all_stable_nodes() while memory is going offline:
+ * it is unsafe for them to touch the stable tree at this time.
+ * But unmerge_ksm_pages(), rmap lookups and other entry points
+ * which do not need the ksm_thread_mutex are all safe.
*/
- mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING);
+ mutex_lock(&ksm_thread_mutex);
+ ksm_run |= KSM_RUN_OFFLINE;
+ mutex_unlock(&ksm_thread_mutex);
break;
case MEM_OFFLINE:
/*
* Most of the work is done by page migration; but there might
* be a few stable_nodes left over, still pointing to struct
- * pages which have been offlined: prune those from the tree.
+ * pages which have been offlined: prune those from the tree,
+ * otherwise get_ksm_page() might later try to access a
+ * non-existent struct page.
*/
- while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
- mn->start_pfn + mn->nr_pages)) != NULL)
- remove_node_from_stable_tree(stable_node);
+ ksm_check_stable_tree(mn->start_pfn,
+ mn->start_pfn + mn->nr_pages);
/* fallthrough */
case MEM_CANCEL_OFFLINE:
+ mutex_lock(&ksm_thread_mutex);
+ ksm_run &= ~KSM_RUN_OFFLINE;
mutex_unlock(&ksm_thread_mutex);
+
+ smp_mb(); /* wake_up_bit advises this */
+ wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
break;
}
return NOTIFY_OK;
}
+#else
+static void wait_while_offlining(void)
+{
+}
#endif /* CONFIG_MEMORY_HOTREMOVE */
#ifdef CONFIG_SYSFS
static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
char *buf)
{
- return sprintf(buf, "%u\n", ksm_run);
+ return sprintf(buf, "%lu\n", ksm_run);
}
static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
*/
mutex_lock(&ksm_thread_mutex);
+ wait_while_offlining();
if (ksm_run != flags) {
ksm_run = flags;
if (flags & KSM_RUN_UNMERGE) {
return -EINVAL;
mutex_lock(&ksm_thread_mutex);
+ wait_while_offlining();
if (ksm_merge_across_nodes != knob) {
- if (ksm_pages_shared)
+ if (ksm_pages_shared || remove_all_stable_nodes())
err = -EBUSY;
- else
+ else if (root_stable_tree == one_stable_tree) {
+ struct rb_root *buf;
+ /*
+ * This is the first time that we switch away from the
+ * default of merging across nodes: must now allocate
+ * a buffer to hold as many roots as may be needed.
+ * Allocate stable and unstable together:
+ * MAXSMP NODES_SHIFT 10 will use 16kB.
+ */
+ buf = kcalloc(nr_node_ids + nr_node_ids,
+ sizeof(*buf), GFP_KERNEL | __GFP_ZERO);
+ /* Let us assume that RB_ROOT is NULL is zero */
+ if (!buf)
+ err = -ENOMEM;
+ else {
+ root_stable_tree = buf;
+ root_unstable_tree = buf + nr_node_ids;
+ /* Stable tree is empty but not the unstable */
+ root_unstable_tree[0] = one_unstable_tree[0];
+ }
+ }
+ if (!err) {
ksm_merge_across_nodes = knob;
+ ksm_nr_node_ids = knob ? 1 : nr_node_ids;
+ }
}
mutex_unlock(&ksm_thread_mutex);
{
struct task_struct *ksm_thread;
int err;
- int nid;
err = ksm_slab_init();
if (err)
goto out;
- for (nid = 0; nid < nr_node_ids; nid++)
- root_stable_tree[nid] = RB_ROOT;
-
ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
if (IS_ERR(ksm_thread)) {
printk(KERN_ERR "ksm: creating kthread failed\n");
#endif /* CONFIG_SYSFS */
#ifdef CONFIG_MEMORY_HOTREMOVE
- /*
- * Choose a high priority since the callback takes ksm_thread_mutex:
- * later callbacks could only be taking locks which nest within that.
- */
+ /* There is no significance to this priority 100 */
hotplug_memory_notifier(ksm_memory_callback, 100);
#endif
return 0;
projects / deliverable / linux.git / blobdiff