mm/gup: local lru_add_drain() to avoid lru_add_drain_all()

In many cases, if collect_longterm_unpinnable_folios() does need to drain
the LRU cache to release a reference, the cache in question is on this
same CPU, and much more efficiently drained by a preliminary local
lru_add_drain(), than the later cross-CPU lru_add_drain_all().

Marked for stable, to counter the increase in lru_add_drain_all()s from
"mm/gup: check ref_count instead of lru before migration".  Note for clean
backports: can take 6.16 commit a03db23 ("gup: optimize longterm
pin_user_pages() for large folio") first.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Hugh Dickins <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Cc: "Aneesh Kumar K.V" <[email protected]>
Cc: Axel Rasmussen <[email protected]>
Cc: Chris Li <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Keir Fraser <[email protected]>
Cc: Konstantin Khlebnikov <[email protected]>
Cc: Li Zhe <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Shivank Garg <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Wei Xu <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: yangge <[email protected]>
Cc: Yuanchu Xie <[email protected]>
Cc: Yu Zhao <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Hugh Dickins

mm/gup.c

@@ -2287,8 +2287,8 @@ static unsigned long collect_longterm_unpinnable_folios(
 		struct pages_or_folios *pofs)
 {
 	unsigned long collected = 0;
-	bool drain_allow = true;
 	struct folio *folio;
+	int drained = 0;
 	long i = 0;
 
 	for (folio = pofs_get_folio(pofs, i); folio;
@@ -2307,10 +2307,17 @@ static unsigned long collect_longterm_unpinnable_folios(
 			continue;
 		}
 
-		if (drain_allow && folio_ref_count(folio) !=
-				   folio_expected_ref_count(folio) + 1) {
+		if (drained == 0 &&
+				folio_ref_count(folio) !=
+				folio_expected_ref_count(folio) + 1) {
+			lru_add_drain();
+			drained = 1;
+		}
+		if (drained == 1 &&
+				folio_ref_count(folio) !=
+				folio_expected_ref_count(folio) + 1) {
 			lru_add_drain_all();
-			drain_allow = false;
+			drained = 2;
 		}
 
 		if (!folio_isolate_lru(folio))