The patch titled
Subject: thp: cleanup split_huge_page()
has been added to the -mm tree. Its filename is
thp-cleanup-split_huge_page.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/thp-cleanup-split_huge_page.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/thp-cleanup-split_huge_page.patch
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------------------------------------------------------
From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Subject: thp: cleanup split_huge_page()
After one of bugfixes to freeze_page(), we don't have freezed pages in
rmap, therefore mapcount of all subpages of freezed THP is zero. And we
have assert for that.
Let's drop code which deal with non-zero mapcount of subpages.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 20 +++++++-------------
1 file changed, 7 insertions(+), 13 deletions(-)
diff -puN mm/huge_memory.c~thp-cleanup-split_huge_page mm/huge_memory.c
--- a/mm/huge_memory.c~thp-cleanup-split_huge_page
+++ a/mm/huge_memory.c
@@ -3217,28 +3217,26 @@ static void unfreeze_page(struct anon_vm
}
}
-static int __split_huge_page_tail(struct page *head, int tail,
+static void __split_huge_page_tail(struct page *head, int tail,
struct lruvec *lruvec, struct list_head *list)
{
- int mapcount;
struct page *page_tail = head + tail;
- mapcount = atomic_read(&page_tail->_mapcount) + 1;
+ VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail);
VM_BUG_ON_PAGE(atomic_read(&page_tail->_count) != 0, page_tail);
/*
* tail_page->_count is zero and not changing from under us. But
* get_page_unless_zero() may be running from under us on the
- * tail_page. If we used atomic_set() below instead of atomic_add(), we
+ * tail_page. If we used atomic_set() below instead of atomic_inc(), we
* would then run atomic_set() concurrently with
* get_page_unless_zero(), and atomic_set() is implemented in C not
* using locked ops. spin_unlock on x86 sometime uses locked ops
* because of PPro errata 66, 92, so unless somebody can guarantee
* atomic_set() here would be safe on all archs (and not only on x86),
- * it's safer to use atomic_add().
+ * it's safer to use atomic_inc().
*/
- atomic_add(mapcount + 1, &page_tail->_count);
-
+ atomic_inc(&page_tail->_count);
page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
page_tail->flags |= (head->flags &
@@ -3272,8 +3270,6 @@ static int __split_huge_page_tail(struct
page_tail->index = head->index + tail;
page_cpupid_xchg_last(page_tail, page_cpupid_last(head));
lru_add_page_tail(head, page_tail, lruvec, list);
-
- return mapcount;
}
static void __split_huge_page(struct page *page, struct list_head *list)
@@ -3281,7 +3277,7 @@ static void __split_huge_page(struct pag
struct page *head = compound_head(page);
struct zone *zone = page_zone(head);
struct lruvec *lruvec;
- int i, tail_mapcount;
+ int i;
/* prevent PageLRU to go away from under us, and freeze lru stats */
spin_lock_irq(&zone->lru_lock);
@@ -3290,10 +3286,8 @@ static void __split_huge_page(struct pag
/* complete memcg works before add pages to LRU */
mem_cgroup_split_huge_fixup(head);
- tail_mapcount = 0;
for (i = HPAGE_PMD_NR - 1; i >= 1; i--)
- tail_mapcount += __split_huge_page_tail(head, i, lruvec, list);
- atomic_sub(tail_mapcount, &head->_count);
+ __split_huge_page_tail(head, i, lruvec, list);
ClearPageCompound(head);
spin_unlock_irq(&zone->lru_lock);
_
Patches currently in -mm which might be from kirill.shutemov@xxxxxxxxxxxxxxx are
mempolicy-do-not-try-to-queue-pages-from-vma_migratable.patch
mm-downgrade-vm_bug-in-isolate_lru_page-to-warning.patch
ipc-shm-handle-removed-segments-gracefully-in-shm_mmap.patch
thp-cleanup-split_huge_page.patch
mm-make-swapin-readahead-to-improve-thp-collapse-rate-fix.patch
mm-make-swapin-readahead-to-improve-thp-collapse-rate-fix-2.patch
mm-make-swapin-readahead-to-improve-thp-collapse-rate-fix-3.patch
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