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

[Usama Arif]

This reverts commit 5da226dbfce3a2f44978c2c7cf88166e69a6788b.

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].

[1] https://lore.kernel.org/all/CAOUHufbkhMZYz20aM_3rHZ3OcK4m2puji2FGpUpn_-DevGk3Kg@xxxxxxxxxxxxxx/
[2] https://lore.kernel.org/all/ZrssOrcJIDy8hacI@xxxxxxxxx/

Signed-off-by: Usama Arif <usamaarif642@xxxxxxxxx>
---
 mm/vmscan.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5dc96a843466..78ad4a141409 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1690,8 +1690,7 @@ 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;
-- 
2.43.5