linux-kernel - [PATCH RFC HACKS 08/11] mm/page_alloc: Simplify gfp

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Message-ID: <20250313-asi-page-alloc-v1-8-04972e046cea@google.com>
Date: Thu, 13 Mar 2025 18:11:27 +0000
From: Brendan Jackman <jackmanb@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	Andrew Morton <akpm@...ux-foundation.org>, David Rientjes <rientjes@...gle.com>, 
	Vlastimil Babka <vbabka@...e.cz>, David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	Mike Rapoport <rppt@...nel.org>, Junaid Shahid <junaids@...gle.com>, Reiji Watanabe <reijiw@...gle.com>, 
	Patrick Bellasi <derkling@...gle.com>, Brendan Jackman <jackmanb@...gle.com>, 
	Yosry Ahmed <yosry.ahmed@...ux.dev>
Subject: [PATCH RFC HACKS 08/11] mm/page_alloc: Simplify gfp_migratetype()

This currently uses optimised bit-hacks to avoid conditional branches
etc. For the purposes of the RFC, let's not get bogged down in those
details - temporarily just drop the bit hacking.

Signed-off-by: Brendan Jackman <jackmanb@...gle.com>
---
 include/linux/gfp.h | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 6bb1a5a7a4ae3392c1cd39cb79271e05512adbeb..23289aa54b6c38a71a908e5a6e034828a75a3b66 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -14,25 +14,20 @@ struct mempolicy;
 
 /* Convert GFP flags to their corresponding migrate type */
 #define GFP_MOVABLE_MASK (__GFP_RECLAIMABLE|__GFP_MOVABLE)
-#define GFP_MOVABLE_SHIFT 3
 
 static inline int gfp_migratetype(const gfp_t gfp_flags)
 {
 	VM_WARN_ON((gfp_flags & GFP_MOVABLE_MASK) == GFP_MOVABLE_MASK);
-	BUILD_BUG_ON((1UL << GFP_MOVABLE_SHIFT) != ___GFP_MOVABLE);
-	BUILD_BUG_ON((___GFP_MOVABLE >> GFP_MOVABLE_SHIFT) != MIGRATE_MOVABLE);
-	BUILD_BUG_ON((___GFP_RECLAIMABLE >> GFP_MOVABLE_SHIFT) != MIGRATE_RECLAIMABLE);
-	BUILD_BUG_ON(((___GFP_MOVABLE | ___GFP_RECLAIMABLE) >>
-		      GFP_MOVABLE_SHIFT) != MIGRATE_HIGHATOMIC);
 
 	if (unlikely(page_group_by_mobility_disabled))
 		return MIGRATE_UNMOVABLE;
 
-	/* Group based on mobility */
-	return (__force unsigned long)(gfp_flags & GFP_MOVABLE_MASK) >> GFP_MOVABLE_SHIFT;
+	switch (gfp_flags & GFP_MOVABLE_MASK) {
+	case __GFP_RECLAIMABLE: return MIGRATE_RECLAIMABLE;
+	case __GFP_MOVABLE: return MIGRATE_MOVABLE;
+	default: return MIGRATE_UNMOVABLE;
+	}
 }
-#undef GFP_MOVABLE_MASK
-#undef GFP_MOVABLE_SHIFT
 
 static inline bool gfpflags_allow_blocking(const gfp_t gfp_flags)
 {

-- 
2.49.0.rc1.451.g8f38331e32-goog