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Date: Mon, 3 Aug 2009 13:15:15 +0100 (BST)
From: Hugh Dickins <hugh.dickins@...cali.co.uk>
To: Izik Eidus <ieidus@...hat.com>
cc: Andrea Arcangeli <aarcange@...hat.com>,
Rik van Riel <riel@...hat.com>,
Chris Wright <chrisw@...hat.com>,
Nick Piggin <nickpiggin@...oo.com.au>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH 6/12] ksm: five little cleanups
1. We don't use __break_cow entry point now: merge it into break_cow.
2. remove_all_slot_rmap_items is just a special case of
remove_trailing_rmap_items: use the latter instead.
3. Extend comment on unmerge_ksm_pages and rmap_items.
4. try_to_merge_two_pages should use try_to_merge_with_ksm_page
instead of duplicating its code; and so swap them around.
5. Comment on cmp_and_merge_page described last year's: update it.
Signed-off-by: Hugh Dickins <hugh.dickins@...cali.co.uk>
---
mm/ksm.c | 112 ++++++++++++++++++++---------------------------------
1 file changed, 44 insertions(+), 68 deletions(-)
--- ksm5/mm/ksm.c 2009-08-02 13:50:07.000000000 +0100
+++ ksm6/mm/ksm.c 2009-08-02 13:50:15.000000000 +0100
@@ -315,22 +315,18 @@ static void break_ksm(struct vm_area_str
/* Which leaves us looping there if VM_FAULT_OOM: hmmm... */
}
-static void __break_cow(struct mm_struct *mm, unsigned long addr)
+static void break_cow(struct mm_struct *mm, unsigned long addr)
{
struct vm_area_struct *vma;
+ down_read(&mm->mmap_sem);
vma = find_vma(mm, addr);
if (!vma || vma->vm_start > addr)
- return;
+ goto out;
if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
- return;
+ goto out;
break_ksm(vma, addr);
-}
-
-static void break_cow(struct mm_struct *mm, unsigned long addr)
-{
- down_read(&mm->mmap_sem);
- __break_cow(mm, addr);
+out:
up_read(&mm->mmap_sem);
}
@@ -439,17 +435,6 @@ static void remove_rmap_item_from_tree(s
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)
{
@@ -471,6 +456,11 @@ static void remove_trailing_rmap_items(s
* 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 void unmerge_ksm_pages(struct vm_area_struct *vma,
unsigned long start, unsigned long end)
@@ -495,7 +485,7 @@ static void unmerge_and_remove_all_rmap_
continue;
unmerge_ksm_pages(vma, vma->vm_start, vma->vm_end);
}
- remove_all_slot_rmap_items(mm_slot);
+ remove_trailing_rmap_items(mm_slot, mm_slot->rmap_list.next);
up_read(&mm->mmap_sem);
}
@@ -533,7 +523,7 @@ static void remove_mm_from_lists(struct
list_del(&mm_slot->mm_list);
spin_unlock(&ksm_mmlist_lock);
- remove_all_slot_rmap_items(mm_slot);
+ remove_trailing_rmap_items(mm_slot, mm_slot->rmap_list.next);
free_mm_slot(mm_slot);
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
}
@@ -740,6 +730,29 @@ 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.
+ */
+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)
+ goto out;
+
+ err = try_to_merge_one_page(vma, page1, kpage);
+out:
+ up_read(&mm1->mmap_sem);
+ return err;
+}
+
+/*
* try_to_merge_two_pages - take two identical pages and prepare them
* to be merged into one page.
*
@@ -772,9 +785,8 @@ static int try_to_merge_two_pages(struct
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;
+ goto out;
}
copy_user_highpage(kpage, page1, addr1, vma);
@@ -782,56 +794,20 @@ static int try_to_merge_two_pages(struct
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);
-
+ err = try_to_merge_with_ksm_page(mm2, addr2, page2, kpage);
/*
- * 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 that fails, we have a ksm page with only one pte
+ * pointing to it: so break it.
*/
if (err)
break_cow(mm1, addr1);
}
-
+out:
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);
-
- 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
@@ -1040,10 +1016,10 @@ static void stable_tree_append(struct rm
}
/*
- * 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().
+ * cmp_and_merge_page - first see if page can be merged into the stable tree;
+ * if not, compare checksum to previous and if it's the same, see if page can
+ * be inserted into the unstable tree, or merged with a page already there and
+ * both transferred to the stable tree.
*
* @page: the page that we are searching identical page to.
* @rmap_item: the reverse mapping into the virtual address of this page
--
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