ksm: cleanup some function arguments

Cleanup: make argument names more consistent from cmp_and_merge_page()
down to replace_page(), so that it's easier to follow the rmap_item's page
and the matching tree_page and the merged kpage through that code.

In some places, e.g.  break_cow(), pass rmap_item instead of separate mm
and address.

cmp_and_merge_page() initialize tree_page to NULL, to avoid a "may be used
uninitialized" warning seen in one config by Anil SB.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 112 insertions, 122 deletions

diff --git a/mm/ksm.c b/mm/ksm.c
index fdd7d5faa90c..54fb3feebb59 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -356,8 +356,10 @@ static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
         return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
 }
 
-static void break_cow(struct mm_struct *mm, unsigned long addr)
+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;
 
         down_read(&mm->mmap_sem);
@@ -665,15 +667,15 @@ out:
 
 /**
  * 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
+ * @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 *oldpage,
-                        struct page *newpage, pte_t orig_pte)
+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;
         pgd_t *pgd;
@@ -684,7 +686,7 @@ static int replace_page(struct vm_area_struct *vma, struct page *oldpage,
         unsigned long addr;
         int err = -EFAULT;
 
-        addr = page_address_in_vma(oldpage, vma);
+        addr = page_address_in_vma(page, vma);
         if (addr == -EFAULT)
                 goto out;
 
@@ -706,15 +708,15 @@ static int replace_page(struct vm_area_struct *vma, struct page *oldpage,
                 goto out;
         }
 
-        get_page(newpage);
-        page_add_ksm_rmap(newpage);
+        get_page(kpage);
+        page_add_ksm_rmap(kpage);
 
         flush_cache_page(vma, addr, pte_pfn(*ptep));
         ptep_clear_flush(vma, addr, ptep);
-        set_pte_at_notify(mm, addr, ptep, mk_pte(newpage, vma->vm_page_prot));
+        set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
 
-        page_remove_rmap(oldpage);
-        put_page(oldpage);
+        page_remove_rmap(page);
+        put_page(page);
 
         pte_unmap_unlock(ptep, ptl);
         err = 0;
@@ -724,26 +726,22 @@ out:
 
 /*
  * 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.
+ * @vma: the vma that holds the pte pointing to page
+ * @page: the PageAnon page that we want to replace with kpage
+ * @kpage: the PageKsm page (or newly allocated page which page_add_ksm_rmap
+ *         will make PageKsm) that we want to map instead of page
  *
  * 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)
+                                 struct page *page, struct page *kpage)
 {
         pte_t orig_pte = __pte(0);
         int err = -EFAULT;
 
         if (!(vma->vm_flags & VM_MERGEABLE))
                 goto out;
-        if (!PageAnon(oldpage))
+        if (!PageAnon(page))
                 goto out;
 
         /*
@@ -753,7 +751,7 @@ static int try_to_merge_one_page(struct vm_area_struct *vma,
          * prefer to continue scanning and merging different pages,
          * then come back to this page when it is unlocked.
          */
-        if (!trylock_page(oldpage))
+        if (!trylock_page(page))
                 goto out;
         /*
          * If this anonymous page is mapped only here, its pte may need
@@ -761,11 +759,11 @@ static int try_to_merge_one_page(struct vm_area_struct *vma,
          * 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) == 0 &&
-            pages_identical(oldpage, newpage))
-                err = replace_page(vma, oldpage, newpage, orig_pte);
+        if (write_protect_page(vma, page, &orig_pte) == 0 &&
+            pages_identical(page, kpage))
+                err = replace_page(vma, page, kpage, orig_pte);
 
-        unlock_page(oldpage);
+        unlock_page(page);
 out:
         return err;
 }
@@ -773,26 +771,26 @@ out:
 /*
  * 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.
+ *
+ * This function returns 0 if the pages were merged, -EFAULT otherwise.
  */
-static int try_to_merge_with_ksm_page(struct mm_struct *mm1,
-                                      unsigned long addr1,
-                                      struct page *page1,
-                                      struct page *kpage)
+static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
+                                      struct page *page, struct page *kpage)
 {
+        struct mm_struct *mm = rmap_item->mm;
         struct vm_area_struct *vma;
         int err = -EFAULT;
 
-        down_read(&mm1->mmap_sem);
-        if (ksm_test_exit(mm1))
+        down_read(&mm->mmap_sem);
+        if (ksm_test_exit(mm))
                 goto out;
-
-        vma = find_vma(mm1, addr1);
-        if (!vma || vma->vm_start > addr1)
+        vma = find_vma(mm, rmap_item->address);
+        if (!vma || vma->vm_start > rmap_item->address)
                 goto out;
 
-        err = try_to_merge_one_page(vma, page1, kpage);
+        err = try_to_merge_one_page(vma, page, kpage);
 out:
-        up_read(&mm1->mmap_sem);
+        up_read(&mm->mmap_sem);
         return err;
 }
 
@@ -800,16 +798,18 @@ out:
  * 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.
+ * This function returns the kpage if we successfully merged two identical
+ * pages into one ksm page, NULL 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)
+static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
+                                           struct page *page,
+                                           struct rmap_item *tree_rmap_item,
+                                           struct page *tree_page)
 {
+        struct mm_struct *mm = rmap_item->mm;
         struct vm_area_struct *vma;
         struct page *kpage;
         int err = -EFAULT;
@@ -820,47 +820,43 @@ static int try_to_merge_two_pages(struct mm_struct *mm1, unsigned long addr1,
          */
         if (ksm_max_kernel_pages &&
             ksm_max_kernel_pages <= ksm_pages_shared)
-                return err;
+                return NULL;
 
         kpage = alloc_page(GFP_HIGHUSER);
         if (!kpage)
-                return err;
-
-        down_read(&mm1->mmap_sem);
-        if (ksm_test_exit(mm1)) {
-                up_read(&mm1->mmap_sem);
-                goto out;
-        }
-        vma = find_vma(mm1, addr1);
-        if (!vma || vma->vm_start > addr1) {
-                up_read(&mm1->mmap_sem);
-                goto out;
-        }
+                return NULL;
 
-        copy_user_highpage(kpage, page1, addr1, vma);
-        err = try_to_merge_one_page(vma, page1, kpage);
-        up_read(&mm1->mmap_sem);
+        down_read(&mm->mmap_sem);
+        if (ksm_test_exit(mm))
+                goto up;
+        vma = find_vma(mm, rmap_item->address);
+        if (!vma || vma->vm_start > rmap_item->address)
+                goto up;
+
+        copy_user_highpage(kpage, page, rmap_item->address, vma);
+        err = try_to_merge_one_page(vma, page, kpage);
+up:
+        up_read(&mm->mmap_sem);
 
         if (!err) {
-                err = try_to_merge_with_ksm_page(mm2, addr2, page2, kpage);
+                err = try_to_merge_with_ksm_page(tree_rmap_item,
+                                                        tree_page, kpage);
                 /*
                  * If that fails, we have a ksm page with only one pte
                  * pointing to it: so break it.
                  */
                 if (err)
-                        break_cow(mm1, addr1);
+                        break_cow(rmap_item);
         }
-out:
-        put_page(kpage);
-        return err;
+        if (err) {
+                put_page(kpage);
+                kpage = NULL;
+        }
+        return kpage;
 }
 
 /*
- * 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
+ * stable_tree_search - search for page inside the stable tree
  *
  * This function checks if there is a page inside the stable tree
  * with identical content to the page that we are scanning right now.
@@ -869,21 +865,21 @@ out:
  * NULL otherwise.
  */
 static struct rmap_item *stable_tree_search(struct page *page,
-                                            struct page **page2,
-                                            struct rmap_item *rmap_item)
+                                            struct page **tree_pagep)
 {
         struct rb_node *node = root_stable_tree.rb_node;
 
         while (node) {
                 struct rmap_item *tree_rmap_item, *next_rmap_item;
+                struct page *tree_page;
                 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])
+                        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);
@@ -892,15 +888,16 @@ static struct rmap_item *stable_tree_search(struct page *page,
                 if (!tree_rmap_item)
                         return NULL;
 
-                ret = memcmp_pages(page, page2[0]);
+                ret = memcmp_pages(page, tree_page);
 
                 if (ret < 0) {
-                        put_page(page2[0]);
+                        put_page(tree_page);
                         node = node->rb_left;
                 } else if (ret > 0) {
-                        put_page(page2[0]);
+                        put_page(tree_page);
                         node = node->rb_right;
                 } else {
+                        *tree_pagep = tree_page;
                         return tree_rmap_item;
                 }
         }
@@ -912,13 +909,9 @@ static struct rmap_item *stable_tree_search(struct page *page,
  * 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,
+static struct rmap_item *stable_tree_insert(struct page *kpage,
                                             struct rmap_item *rmap_item)
 {
         struct rb_node **new = &root_stable_tree.rb_node;
@@ -943,7 +936,7 @@ static struct rmap_item *stable_tree_insert(struct page *page,
                 if (!tree_rmap_item)
                         return NULL;
 
-                ret = memcmp_pages(page, tree_page);
+                ret = memcmp_pages(kpage, tree_page);
                 put_page(tree_page);
 
                 parent = *new;
@@ -971,12 +964,8 @@ static struct rmap_item *stable_tree_insert(struct page *page,
 }
 
 /*
- * 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
+ * unstable_tree_search_insert - search for identical page,
+ * else insert rmap_item into the unstable tree.
  *
  * 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
@@ -988,42 +977,45 @@ static struct rmap_item *stable_tree_insert(struct page *page,
  * 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)
+static
+struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
+                                              struct page *page,
+                                              struct page **tree_pagep)
+
 {
         struct rb_node **new = &root_unstable_tree.rb_node;
         struct rb_node *parent = NULL;
 
         while (*new) {
                 struct rmap_item *tree_rmap_item;
+                struct page *tree_page;
                 int ret;
 
                 cond_resched();
                 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
-                page2[0] = get_mergeable_page(tree_rmap_item);
-                if (!page2[0])
+                tree_page = get_mergeable_page(tree_rmap_item);
+                if (!tree_page)
                         return NULL;
 
                 /*
-                 * Don't substitute an unswappable ksm page
-                 * just for one good swappable forked page.
+                 * Don't substitute a ksm page for a forked page.
                  */
-                if (page == page2[0]) {
-                        put_page(page2[0]);
+                if (page == tree_page) {
+                        put_page(tree_page);
                         return NULL;
                 }
 
-                ret = memcmp_pages(page, page2[0]);
+                ret = memcmp_pages(page, tree_page);
 
                 parent = *new;
                 if (ret < 0) {
-                        put_page(page2[0]);
+                        put_page(tree_page);
                         new = &parent->rb_left;
                 } else if (ret > 0) {
-                        put_page(page2[0]);
+                        put_page(tree_page);
                         new = &parent->rb_right;
                 } else {
+                        *tree_pagep = tree_page;
                         return tree_rmap_item;
                 }
         }
@@ -1068,24 +1060,23 @@ static void stable_tree_append(struct rmap_item *rmap_item,
  */
 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
 {
-        struct page *page2[1];
         struct rmap_item *tree_rmap_item;
+        struct page *tree_page = NULL;
+        struct page *kpage;
         unsigned int checksum;
         int err;
 
         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);
+        tree_rmap_item = stable_tree_search(page, &tree_page);
         if (tree_rmap_item) {
-                if (page == page2[0])                   /* forked */
+                kpage = tree_page;
+                if (page == kpage)                      /* forked */
                         err = 0;
                 else
-                        err = try_to_merge_with_ksm_page(rmap_item->mm,
-                                                         rmap_item->address,
-                                                         page, page2[0]);
-                put_page(page2[0]);
-
+                        err = try_to_merge_with_ksm_page(rmap_item,
+                                                         page, kpage);
                 if (!err) {
                         /*
                          * The page was successfully merged:
@@ -1093,6 +1084,7 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
                          */
                         stable_tree_append(rmap_item, tree_rmap_item);
                 }
+                put_page(kpage);
                 return;
         }
 
@@ -1103,7 +1095,7 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
          * when the mem_cgroup had reached its limit: try again now.
          */
         if (PageKsm(page))
-                break_cow(rmap_item->mm, rmap_item->address);
+                break_cow(rmap_item);
 
         /*
          * In case the hash value of the page was changed from the last time we
@@ -1117,18 +1109,18 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
                 return;
         }
 
-        tree_rmap_item = unstable_tree_search_insert(page, page2, rmap_item);
+        tree_rmap_item =
+                unstable_tree_search_insert(rmap_item, page, &tree_page);
         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]);
+                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 (!err) {
+                if (kpage) {
                         remove_rmap_item_from_tree(tree_rmap_item);
 
                         /*
@@ -1137,16 +1129,14 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
                          * 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))
+                        if (stable_tree_insert(kpage, 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);
+                                break_cow(tree_rmap_item);
+                                break_cow(rmap_item);
                         }
+                        put_page(kpage);
                 }
-
-                put_page(page2[0]);
         }
 }
 
@@ -1308,7 +1298,7 @@ static void ksm_do_scan(unsigned int scan_npages)
                         /*
                          * Replace now-unshared ksm page by ordinary page.
                          */
-                        break_cow(rmap_item->mm, rmap_item->address);
+                        break_cow(rmap_item);
                         remove_rmap_item_from_tree(rmap_item);
                         rmap_item->oldchecksum = calc_checksum(page);
                 }