[PATCH 1/2] mm/vmscan: restore sc->gfp_mask after promoting it to __GFP_HIGHMEM

[Weijie Yang]

We promote sc->gfp_mask to __GFP_HIGHMEM to forcibly scan highmem if
there are too many buffer_heads pinning highmem. see: cc715d99e5

This patch restores sc->gfp_mask to its caller original value after
finishing the scan job, to avoid the impact on other invocations from
its upper caller, such as vmpressure_prio(), shrink_slab().

Signed-off-by: Weijie Yang <weijie.yang@xxxxxxxxxxx>
---
 mm/vmscan.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)
 mode change 100644 => 100755 mm/vmscan.c

diff --git a/mm/vmscan.c b/mm/vmscan.c
old mode 100644
new mode 100755
index a9c74b4..35879f0
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2298,14 +2298,17 @@ static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
 	unsigned long nr_soft_reclaimed;
 	unsigned long nr_soft_scanned;
 	bool aborted_reclaim = false;
+	bool promoted_mask = false;
 
 	/*
 	 * If the number of buffer_heads in the machine exceeds the maximum
 	 * allowed level, force direct reclaim to scan the highmem zone as
 	 * highmem pages could be pinning lowmem pages storing buffer_heads
 	 */
-	if (buffer_heads_over_limit)
+	if (buffer_heads_over_limit) {
+		promoted_mask = !(sc->gfp_mask & __GFP_HIGHMEM);
 		sc->gfp_mask |= __GFP_HIGHMEM;
+	}
 
 	for_each_zone_zonelist_nodemask(zone, z, zonelist,
 					gfp_zone(sc->gfp_mask), sc->nodemask) {
@@ -2354,6 +2357,9 @@ static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
 		shrink_zone(zone, sc);
 	}
 
+	if (promoted_mask)
+		sc->gfp_mask &= ~__GFP_HIGHMEM;
+
 	return aborted_reclaim;
 }
 
-- 
1.7.10.4


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