linux-kernel - [PATCH 1/3] dma/pool: Improve pool lookup

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Message-Id: <c846b1a2f43295cac926c7af2ce907f62baec518.1768230104.git.robin.murphy@arm.com>
Date: Mon, 12 Jan 2026 15:46:36 +0000
From: Robin Murphy <robin.murphy@....com>
To: m.szyprowski@...sung.com,
	akpm@...ux-foundation.org,
	vbabka@...e.cz,
	david@...nel.org
Cc: bhe@...hat.com,
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	vladimir.kondratiev@...ileye.com,
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Subject: [PATCH 1/3] dma/pool: Improve pool lookup

If CONFIG_ZONE_DMA32 is enabled, but we have not allocated the
corresponding atomic_pool_dma32, dma_guess_pool() may return the NULL
value of that and fail a GFP_DMA32 allocation without trying to fall
back to other pools which may exist. Furthermore, if no GFP_DMA pool
exists, it is preferable to try GFP_DMA32 rather than immediately fall
back to GFP_KERNEL with even less chance of success. Improve matters
by encoding an explicit order of pool preference for each flag.

Signed-off-by: Robin Murphy <robin.murphy@....com>
---
 kernel/dma/pool.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
index 26392badc36b..2645cfb5718b 100644
--- a/kernel/dma/pool.c
+++ b/kernel/dma/pool.c
@@ -224,10 +224,10 @@ postcore_initcall(dma_atomic_pool_init);
 static inline struct gen_pool *dma_guess_pool(struct gen_pool *prev, gfp_t gfp)
 {
 	if (prev == NULL) {
-		if (IS_ENABLED(CONFIG_ZONE_DMA32) && (gfp & GFP_DMA32))
-			return atomic_pool_dma32;
-		if (atomic_pool_dma && (gfp & GFP_DMA))
-			return atomic_pool_dma;
+		if (gfp & GFP_DMA)
+			return atomic_pool_dma ?: atomic_pool_dma32 ?: atomic_pool_kernel;
+		if (gfp & GFP_DMA32)
+			return atomic_pool_dma32 ?: atomic_pool_dma ?: atomic_pool_kernel;
 		return atomic_pool_kernel;
 	}
 	if (prev == atomic_pool_kernel)
-- 
2.34.1