参照元†
- struct page *page
- struct list_head *list
返り値†
static void __split_huge_page_refcount(struct page *page,
struct list_head *list)
{
int i;
struct zone *zone = page_zone(page);
struct lruvec *lruvec;
int tail_count = 0;
/* prevent PageLRU to go away from under us, and freeze lru stats */
spin_lock_irq(&zone->lru_lock);
lruvec = mem_cgroup_page_lruvec(page, zone);
compound_lock(page);
/* complete memcg works before add pages to LRU */
mem_cgroup_split_huge_fixup(page);
for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
struct page *page_tail = page + i;
/* tail_page->_mapcount cannot change */
BUG_ON(page_mapcount(page_tail) < 0);
tail_count += page_mapcount(page_tail);
/* check for overflow */
BUG_ON(tail_count < 0);
BUG_ON(atomic_read(&page_tail->_count) != 0);
/*
* 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
* 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().
*/
atomic_add(page_mapcount(page) + page_mapcount(page_tail) + 1,
&page_tail->_count);
/* after clearing PageTail the gup refcount can be released */
smp_mb__after_atomic();
page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
page_tail->flags |= (page->flags &
((1L << PG_referenced) |
(1L << PG_swapbacked) |
(1L << PG_mlocked) |
(1L << PG_uptodate) |
(1L << PG_active) |
(1L << PG_unevictable)));
page_tail->flags |= (1L << PG_dirty);
clear_compound_head(page_tail);
if (page_is_young(page))
set_page_young(page_tail);
if (page_is_idle(page))
set_page_idle(page_tail);
/*
* __split_huge_page_splitting() already set the
* splitting bit in all pmd that could map this
* hugepage, that will ensure no CPU can alter the
* mapcount on the head page. The mapcount is only
* accounted in the head page and it has to be
* transferred to all tail pages in the below code. So
* for this code to be safe, the split the mapcount
* can't change. But that doesn't mean userland can't
* keep changing and reading the page contents while
* we transfer the mapcount, so the pmd splitting
* status is achieved setting a reserved bit in the
* pmd, not by clearing the present bit.
*/
page_tail->_mapcount = page->_mapcount;
BUG_ON(page_tail->mapping);
page_tail->mapping = page->mapping;
page_tail->index = page->index + i;
page_cpupid_xchg_last(page_tail, page_cpupid_last(page));
BUG_ON(!PageAnon(page_tail));
BUG_ON(!PageUptodate(page_tail));
BUG_ON(!PageDirty(page_tail));
BUG_ON(!PageSwapBacked(page_tail));
lru_add_page_tail(page, page_tail, lruvec, list);
}
atomic_sub(tail_count, &page->_count);
BUG_ON(atomic_read(&page->_count) <= 0);
__mod_zone_page_state(zone, NR_ANON_TRANSPARENT_HUGEPAGES, -1);
ClearPageCompound(page);
compound_unlock(page);
spin_unlock_irq(&zone->lru_lock);
for (i = 1; i < HPAGE_PMD_NR; i++) {
struct page *page_tail = page + i;
BUG_ON(page_count(page_tail) <= 0);
/*
* Tail pages may be freed if there wasn't any mapping
* like if add_to_swap() is running on a lru page that
* had its mapping zapped. And freeing these pages
* requires taking the lru_lock so we do the put_page
* of the tail pages after the split is complete.
*/
put_page(page_tail);
}
/*
* Only the head page (now become a regular page) is required
* to be pinned by the caller.
*/
BUG_ON(page_count(page) <= 0);
}
コメント†
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