[PATCH v12 11/16] mm/mlock: reorder isolation sequence during munlock

Alex Shi
2020-06-11T06:16:44Z

This patch reorder the isolation steps during munlock, move the lru lock
to guard each pages, unfold __munlock_isolate_lru_page func, to do the
preparation for lru lock change.

__split_huge_page_refcount doesn't exist, but we still have to guard
PageMlocked and PageLRU in __split_huge_page_tail.

[lkp@intel.com: found a sleeping function bug ... at mm/rmap.c]
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
---
mm/mlock.c | 93 ++++++++++++++++++++++++++++++++++----------------------------
1 file changed, 51 insertions(+), 42 deletions(-)

diff --git a/mm/mlock.c b/mm/mlock.c
index 228ba5a8e0a5..7098be122966 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -103,25 +103,6 @@ void mlock_vma_page(struct page *page)
}

/*
- * Isolate a page from LRU with optional get_page() pin.
- * Assumes lru_lock already held and page already pinned.
- */
-static bool __munlock_isolate_lru_page(struct page *page, bool getpage)
-{
- if (TestClearPageLRU(page)) {
- struct lruvec *lruvec;
-
- lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));
- if (getpage)
- get_page(page);
- del_page_from_lru_list(page, lruvec, page_lru(page));
- return true;
- }
-
- return false;
-}
-
-/*
* Finish munlock after successful page isolation
*
* Page must be locked. This is a wrapper for try_to_munlock()
@@ -181,6 +162,7 @@ static void __munlock_isolation_failed(struct page *page)
unsigned int munlock_vma_page(struct page *page)
{
int nr_pages;
+ bool clearlru = false;
pg_data_t *pgdat = page_pgdat(page);

/* For try_to_munlock() and to serialize with page migration */
@@ -189,32 +171,42 @@ unsigned int munlock_vma_page(struct page *page)
VM_BUG_ON_PAGE(PageTail(page), page);

/*
- * Serialize with any parallel __split_huge_page_refcount() which
+ * Serialize with any parallel __split_huge_page_tail() which
* might otherwise copy PageMlocked to part of the tail pages before
* we clear it in the head page. It also stabilizes hpage_nr_pages().
*/
+ get_page(page);
spin_lock_irq(&pgdat->lru_lock);
+ clearlru = TestClearPageLRU(page);

if (!TestClearPageMlocked(page)) {
- /* Potentially, PTE-mapped THP: do not skip the rest PTEs */
- nr_pages = 1;
- goto unlock_out;
+ if (clearlru)
+ SetPageLRU(page);
+ /*
+ * Potentially, PTE-mapped THP: do not skip the rest PTEs
+ * Reuse lock as memory barrier for release_pages racing.
+ */
+ spin_unlock_irq(&pgdat->lru_lock);
+ put_page(page);
+ return 0;
}

nr_pages = hpage_nr_pages(page);
__mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages);

- if (__munlock_isolate_lru_page(page, true)) {
+ if (clearlru) {
+ struct lruvec *lruvec;
+
+ lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));
+ del_page_from_lru_list(page, lruvec, page_lru(page));
spin_unlock_irq(&pgdat->lru_lock);
__munlock_isolated_page(page);
- goto out;
+ } else {
+ spin_unlock_irq(&pgdat->lru_lock);
+ put_page(page);
+ __munlock_isolation_failed(page);
}
- __munlock_isolation_failed(page);
-
-unlock_out:
- spin_unlock_irq(&pgdat->lru_lock);

-out:
return nr_pages - 1;
}

@@ -297,34 +289,51 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
pagevec_init(&pvec_putback);

/* Phase 1: page isolation */
- spin_lock_irq(&zone->zone_pgdat->lru_lock);
for (i = 0; i < nr; i++) {
struct page *page = pvec->pages[i];
+ struct lruvec *lruvec;
+ bool clearlru;

- if (TestClearPageMlocked(page)) {
- /*
- * We already have pin from follow_page_mask()
- * so we can spare the get_page() here.
- */
- if (__munlock_isolate_lru_page(page, false))
- continue;
- else
- __munlock_isolation_failed(page);
- } else {
+ clearlru = TestClearPageLRU(page);
+ spin_lock_irq(&zone->zone_pgdat->lru_lock);
+
+ if (!TestClearPageMlocked(page)) {
delta_munlocked++;
+ if (clearlru)
+ SetPageLRU(page);
+ goto putback;
+ }
+
+ if (!clearlru) {
+ __munlock_isolation_failed(page);
+ goto putback;
}

/*
+ * Isolate this page.
+ * We already have pin from follow_page_mask()
+ * so we can spare the get_page() here.
+ */
+ lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));
+ del_page_from_lru_list(page, lruvec, page_lru(page));
+ spin_unlock_irq(&zone->zone_pgdat->lru_lock);
+ continue;
+
+ /*
* We won't be munlocking this page in the next phase
* but we still need to release the follow_page_mask()
* pin. We cannot do it under lru_lock however. If it's
* the last pin, __page_cache_release() would deadlock.
*/
+putback:
+ spin_unlock_irq(&zone->zone_pgdat->lru_lock);
pagevec_add(&pvec_putback, pvec->pages[i]);
pvec->pages[i] = NULL;
}
+ /* tempary disable irq, will remove later */
+ local_irq_disable();
__mod_zone_page_state(zone, NR_MLOCK, delta_munlocked);
- spin_unlock_irq(&zone->zone_pgdat->lru_lock);
+ local_irq_enable();

/* Now we can release pins of pages that we are not munlocking */
pagevec_release(&pvec_putback);
--
1.8.3.1