[PATCH 41/62] shmem: Convert shmem_wait_for_pins to XArray

Matthew Wilcox
2017-11-22T21:14:26Z

As with shmem_tag_pins(), hold the lock around the entire loop instead
of acquiring & dropping it for each entry we're going to untag.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
---
mm/shmem.c | 59 +++++++++++++++++++++++++----------------------------------
1 file changed, 25 insertions(+), 34 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 302fcb62ba1f..e4d28743a666 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2636,9 +2636,7 @@ static void shmem_tag_pins(struct address_space *mapping)
*/
static int shmem_wait_for_pins(struct address_space *mapping)
{
- struct radix_tree_iter iter;
- void **slot;
- pgoff_t start;
+ XA_STATE(xas, 0);
struct page *page;
int error, scan;

@@ -2646,7 +2644,9 @@ static int shmem_wait_for_pins(struct address_space *mapping)

error = 0;
for (scan = 0; scan <= LAST_SCAN; scan++) {
- if (!radix_tree_tagged(&mapping->pages, SHMEM_TAG_PINNED))
+ unsigned int tagged = 0;
+
+ if (!xa_tagged(&mapping->pages, SHMEM_TAG_PINNED))
break;

if (!scan)
@@ -2654,45 +2654,36 @@ static int shmem_wait_for_pins(struct address_space *mapping)
else if (schedule_timeout_killable((HZ << scan) / 200))
scan = LAST_SCAN;

- start = 0;
- rcu_read_lock();
- radix_tree_for_each_tagged(slot, &mapping->pages, &iter,
- start, SHMEM_TAG_PINNED) {
-
- page = radix_tree_deref_slot(slot);
- if (radix_tree_exception(page)) {
- if (radix_tree_deref_retry(page)) {
- slot = radix_tree_iter_retry(&iter);
- continue;
- }
-
- page = NULL;
- }
-
- if (page &&
- page_count(page) - page_mapcount(page) != 1) {
- if (scan < LAST_SCAN)
- goto continue_resched;
-
+ xas_set(&xas, 0);
+ xa_lock_irq(&mapping->pages);
+ xas_for_each_tag(&mapping->pages, &xas, page, ULONG_MAX,
+ SHMEM_TAG_PINNED) {
+ bool clear = true;
+ if (xa_is_value(page))
+ continue;
+ if (page_count(page) - page_mapcount(page) != 1) {
/*
* On the last scan, we clean up all those tags
* we inserted; but make a note that we still
* found pages pinned.
*/
- error = -EBUSY;
+ if (scan == LAST_SCAN)
+ error = -EBUSY;
+ else
+ clear = false;
}
+ if (clear)
+ xas_clear_tag(&mapping->pages, &xas,
+ SHMEM_TAG_PINNED);
+ if (++tagged % XA_CHECK_SCHED)
+ continue;

- xa_lock_irq(&mapping->pages);
- radix_tree_tag_clear(&mapping->pages,
- iter.index, SHMEM_TAG_PINNED);
+ xas_pause(&xas);
xa_unlock_irq(&mapping->pages);
-continue_resched:
- if (need_resched()) {
- slot = radix_tree_iter_resume(slot, &iter);
- cond_resched_rcu();
- }
+ cond_resched();
+ xa_lock_irq(&mapping->pages);
}
- rcu_read_unlock();
+ xa_unlock_irq(&mapping->pages);
}

return error;
--
2.15.0