Revert "mm: skip CMA pages when they are not available"

This reverts commit 5da226d ("mm: skip CMA pages when they are not
available") and b7108d6 ("Multi-gen LRU: skip CMA pages when they are
not eligible").

lruvec->lru_lock is highly contended and is held when calling
isolate_lru_folios.  If the lru has a large number of CMA folios
consecutively, while the allocation type requested is not MIGRATE_MOVABLE,
isolate_lru_folios can hold the lock for a very long time while it skips
those.  For FIO workload, ~150million order=0 folios were skipped to
isolate a few ZONE_DMA folios [1].  This can cause lockups [1] and high
memory pressure for extended periods of time [2].

Remove skipping CMA for MGLRU as well, as it was introduced in sort_folio
for the same resaon as 5da226d.

[1] https://lore.kernel.org/all/CAOUHufbkhMZYz20aM_3rHZ3OcK4m2puji2FGpUpn_-DevGk3Kg@mail.gmail.com/
[2] https://lore.kernel.org/all/[email protected]/

[[email protected]: also revert b7108d6, per Johannes]
  Link: https://lkml.kernel.org/r/[email protected]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Fixes: 5da226d ("mm: skip CMA pages when they are not available")
Signed-off-by: Usama Arif <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Cc: Bharata B Rao <[email protected]>
Cc: Breno Leitao <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Yu Zhao <[email protected]>
Cc: Zhaoyang Huang <[email protected]>
Cc: Zhaoyang Huang <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: uarif1

mm/vmscan.c

@@ -1604,25 +1604,6 @@ static __always_inline void update_lru_sizes(struct lruvec *lruvec,
 
 }
 
-#ifdef CONFIG_CMA
-/*
- * It is waste of effort to scan and reclaim CMA pages if it is not available
- * for current allocation context. Kswapd can not be enrolled as it can not
- * distinguish this scenario by using sc->gfp_mask = GFP_KERNEL
- */
-static bool skip_cma(struct folio *folio, struct scan_control *sc)
-{
-	return !current_is_kswapd() &&
-			gfp_migratetype(sc->gfp_mask) != MIGRATE_MOVABLE &&
-			folio_migratetype(folio) == MIGRATE_CMA;
-}
-#else
-static bool skip_cma(struct folio *folio, struct scan_control *sc)
-{
-	return false;
-}
-#endif
-
 /*
  * Isolating page from the lruvec to fill in @dst list by nr_to_scan times.
  *
@@ -1669,8 +1650,7 @@ static unsigned long isolate_lru_folios(unsigned long nr_to_scan,
 		nr_pages = folio_nr_pages(folio);
 		total_scan += nr_pages;
 
-		if (folio_zonenum(folio) > sc->reclaim_idx ||
-				skip_cma(folio, sc)) {
+		if (folio_zonenum(folio) > sc->reclaim_idx) {
 			nr_skipped[folio_zonenum(folio)] += nr_pages;
 			move_to = &folios_skipped;
 			goto move;
@@ -4320,7 +4300,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
 	}
 
 	/* ineligible */
-	if (zone > sc->reclaim_idx || skip_cma(folio, sc)) {
+	if (zone > sc->reclaim_idx) {
 		gen = folio_inc_gen(lruvec, folio, false);
 		list_move_tail(&folio->lru, &lrugen->folios[gen][type][zone]);
 		return true;