[PATCH V2 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>
---
Changes since v1:
	- use orig_mask to record the caller's orininal mask and restore
	 it after finishing scan, according to Riel's suggestion.

V1: https://lkml.org/lkml/2014/2/12/764

 mm/vmscan.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index a9c74b4..da0a87c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2298,6 +2298,7 @@ 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;
+	gfp_t orig_mask = sc->gfp_mask;
 
 	/*
 	 * If the number of buffer_heads in the machine exceeds the maximum
@@ -2354,6 +2355,12 @@ static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
 		shrink_zone(zone, sc);
 	}
 
+	/*
+	 * restore to original mask to avoid the impact on its caller
+	 * if we promote it to __GFP_HIGHMEM.
+	 */
+	sc->gfp_mask = orig_mask;
+
 	return aborted_reclaim;
 }
 
-- 
1.7.10.4


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