[PATCHv6 15/36] ksm: prepare to new THP semantics

Kirill A. Shutemov
2015-06-03T17:07:10Z

We don't need special code to stabilize THP. If you've got reference to
any subpage of THP it will not be split under you.

New split_huge_page() also accepts tail pages: no need in special code
to get reference to head page.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Tested-by: Sasha Levin <sasha.levin@oracle.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
---
mm/ksm.c | 57 ++++++++++-----------------------------------------------
1 file changed, 10 insertions(+), 47 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index fe09f3ddc912..fb333d8188fc 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -441,20 +441,6 @@ static void break_cow(struct rmap_item *rmap_item)
up_read(&mm->mmap_sem);
}

-static struct page *page_trans_compound_anon(struct page *page)
-{
- if (PageTransCompound(page)) {
- struct page *head = compound_head(page);
- /*
- * head may actually be splitted and freed from under
- * us but it's ok here.
- */
- if (PageAnon(head))
- return head;
- }
- return NULL;
-}
-
static struct page *get_mergeable_page(struct rmap_item *rmap_item)
{
struct mm_struct *mm = rmap_item->mm;
@@ -470,7 +456,7 @@ static struct page *get_mergeable_page(struct rmap_item *rmap_item)
page = follow_page(vma, addr, FOLL_GET);
if (IS_ERR_OR_NULL(page))
goto out;
- if (PageAnon(page) || page_trans_compound_anon(page)) {
+ if (PageAnon(page)) {
flush_anon_page(vma, page, addr);
flush_dcache_page(page);
} else {
@@ -976,33 +962,6 @@ out:
return err;
}

-static int page_trans_compound_anon_split(struct page *page)
-{
- int ret = 0;
- struct page *transhuge_head = page_trans_compound_anon(page);
- if (transhuge_head) {
- /* Get the reference on the head to split it. */
- if (get_page_unless_zero(transhuge_head)) {
- /*
- * Recheck we got the reference while the head
- * was still anonymous.
- */
- if (PageAnon(transhuge_head))
- ret = split_huge_page(transhuge_head);
- else
- /*
- * Retry later if split_huge_page run
- * from under us.
- */
- ret = 1;
- put_page(transhuge_head);
- } else
- /* Retry later if split_huge_page run from under us. */
- ret = 1;
- }
- return ret;
-}
-
/*
* try_to_merge_one_page - take two pages and merge them into one
* @vma: the vma that holds the pte pointing to page
@@ -1023,9 +982,6 @@ static int try_to_merge_one_page(struct vm_area_struct *vma,

if (!(vma->vm_flags & VM_MERGEABLE))
goto out;
- if (PageTransCompound(page) && page_trans_compound_anon_split(page))
- goto out;
- BUG_ON(PageTransCompound(page));
if (!PageAnon(page))
goto out;

@@ -1038,6 +994,13 @@ static int try_to_merge_one_page(struct vm_area_struct *vma,
*/
if (!trylock_page(page))
goto out;
+
+ if (PageTransCompound(page)) {
+ err = split_huge_page(page);
+ if (err)
+ goto out_unlock;
+ }
+
/*
* If this anonymous page is mapped only here, its pte may need
* to be write-protected. If it's mapped elsewhere, all of its
@@ -1068,6 +1031,7 @@ static int try_to_merge_one_page(struct vm_area_struct *vma,
}
}

+out_unlock:
unlock_page(page);
out:
return err;
@@ -1620,8 +1584,7 @@ next_mm:
cond_resched();
continue;
}
- if (PageAnon(*page) ||
- page_trans_compound_anon(*page)) {
+ if (PageAnon(*page)) {
flush_anon_page(vma, *page, ksm_scan.address);
flush_dcache_page(*page);
rmap_item = get_next_rmap_item(slot,
--
2.1.4