mm/huge_memory: move THP gfp limit helper into header

Shmem has some special requirements for THP GFP and has to limit it in
certain zones or provide a more lenient fallback.

We'll use this helper for generic swap THP allocation, which needs to
support shmem.  For a typical GFP_HIGHUSER_MOVABLE swap-in, this helper is
basically a no-op.  But it's necessary for certain shmem users, mostly
drivers.

No feature change.

Link: https://lore.kernel.org/20260517-swap-table-p4-v5-3-88ae43e064c7@tencent.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Acked-by: Chris Li <chrisl@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Youngjun Park <youngjun.park@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 30 insertions, 0 deletions

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 2949e5acff35..58382e97a66d 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -238,6 +238,31 @@ static inline bool thp_vma_suitable_order(struct vm_area_struct *vma,
 }
 
 /*
+ * Make sure huge_gfp is always more limited than limit_gfp.
+ * Some shmem users want THP allocation to be done less aggressively
+ * and only in certain zone.
+ */
+static inline gfp_t thp_shmem_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 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,
+	 * and the intersection of the allow flags.
+	 */
+	result |= (limit_gfp & denyflags);
+	result |= (huge_gfp & limit_gfp) & allowflags;
+
+	return result;
+}
+
+/*
  * Filter the bitfield of input orders to the ones suitable for use in the vma.
  * See thp_vma_suitable_order().
  * All orders that pass the checks are returned as a bitfield.
@@ -581,6 +606,11 @@ static inline bool thp_vma_suitable_order(struct vm_area_struct *vma,
 	return false;
 }
 
+static inline gfp_t thp_shmem_limit_gfp_mask(gfp_t huge_gfp, gfp_t limit_gfp)
+{
+	return huge_gfp;
+}
+
 static inline unsigned long thp_vma_suitable_orders(struct vm_area_struct *vma,
 		unsigned long addr, unsigned long orders)
 {