mm,shmem,thp: limit shmem THP allocations to requested zones

Hugh pointed out that the gma500 driver uses shmem pages, but needs to
limit them to the DMA32 zone.  Ensure the allocations resulting from the
gfp_mask returned by limit_gfp_mask use the zone flags that were
originally passed to shmem_getpage_gfp.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Rik van Riel <[email protected]>
Suggested-by: Hugh Dickins <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Xu Yu <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/shmem.c

@@ -1513,7 +1513,11 @@ static gfp_t limit_gfp_mask(gfp_t huge_gfp, gfp_t limit_gfp)
 {
 	gfp_t allowflags = __GFP_IO | __GFP_FS | __GFP_RECLAIM;
 	gfp_t denyflags = __GFP_NOWARN | __GFP_NORETRY;
-	gfp_t result = huge_gfp & ~allowflags;
+	gfp_t zoneflags = limit_gfp & GFP_ZONEMASK;
+	gfp_t result = huge_gfp & ~(allowflags | GFP_ZONEMASK);
+
+	/* Allow allocations only from the originally specified zones. */
+	result |= zoneflags;
 
 	/*
 	 * Minimize the result gfp by taking the union with the deny flags,