ksm: prepare to new THP semantics
authorKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Sat, 16 Jan 2016 00:53:03 +0000 (16:53 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Sat, 16 Jan 2016 01:56:32 +0000 (17:56 -0800)
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>
Tested-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Steve Capper <steve.capper@linaro.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/ksm.c

index b4f7b69efad04416cb91b72062edb15523bfc35b..80c29b1b2b8af3b631dfb30954794560394f1af0 100644 (file)
--- 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 {
@@ -975,33 +961,6 @@ 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
@@ -1020,9 +979,6 @@ static int try_to_merge_one_page(struct vm_area_struct *vma,
        if (page == kpage)                      /* ksm page forked */
                return 0;
 
-       if (PageTransCompound(page) && page_trans_compound_anon_split(page))
-               goto out;
-       BUG_ON(PageTransCompound(page));
        if (!PageAnon(page))
                goto out;
 
@@ -1035,6 +991,13 @@ 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
@@ -1065,6 +1028,7 @@ static int try_to_merge_one_page(struct vm_area_struct *vma,
                }
        }
 
+out_unlock:
        unlock_page(page);
 out:
        return err;
@@ -1635,8 +1599,7 @@ 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,