Commit 81464e30 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

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: default avatarHugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: default avatarIzik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 6e158384

mm/ksm.c

+44 −68
Original line number Diff line number Diff line
@@ -315,22 +315,18 @@ static void break_ksm(struct vm_area_struct *vma, unsigned long addr) 
	/* 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(struct rmap_item *rmap_item) 
	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(struct mm_slot *mm_slot, 
 * 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_items(void) 
				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 mm_struct *mm) 
	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);

}
@@ -739,6 +729,29 @@ out: 
	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)

		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 mm_struct *mm1, unsigned long addr1, 
	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);
@@ -782,55 +794,19 @@ static int try_to_merge_two_pages(struct mm_struct *mm1, unsigned long addr1, 
	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.
@@ -1033,10 +1009,10 @@ static void stable_tree_append(struct rmap_item *rmap_item, 
}



/*

 * 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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