thp: change deferred_split_count() to return number of THP in queue

I've got meaning of shrinker::count_objects() wrong: it should return
number of potentially freeable objects, which is not necessary correlate
with freeable memory.

Returning 256 per THP in queue is not reasonable:
shrinker::scan_objects() never called with nr_to_scan > 128 in my setup.

Let's return 1 per THP and correct scan_object accordingly.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: 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: Vlastimil Babka <vbabka@suse.cz>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 7 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 253a25e007d7..7aae72114583 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3465,12 +3465,7 @@ static unsigned long deferred_split_count(struct shrinker *shrink,
                 struct shrink_control *sc)
 {
         struct pglist_data *pgdata = NODE_DATA(sc->nid);
-        /*
-         * Split a page from split_queue will free up at least one page,
-         * at most HPAGE_PMD_NR - 1. We don't track exact number.
-         * Let's use HPAGE_PMD_NR / 2 as ballpark.
-         */
-        return ACCESS_ONCE(pgdata->split_queue_len) * HPAGE_PMD_NR / 2;
+        return ACCESS_ONCE(pgdata->split_queue_len);
 }
 
 static unsigned long deferred_split_scan(struct shrinker *shrink,
@@ -3511,7 +3506,13 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
         list_splice_tail(&list, &pgdata->split_queue);
         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
 
-        return split * HPAGE_PMD_NR / 2;
+        /*
+         * Stop shrinker if we didn't split any page, but the queue is empty.
+         * This can happen if pages were freed under us.
+         */
+        if (!split && list_empty(&pgdata->split_queue))
+                return SHRINK_STOP;
+        return split;
 }
 
 static struct shrinker deferred_split_shrinker = {