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>

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 253a25e..7aae721 100644 (file)
--- 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 = {