[PATCH v19 38/40] mm: percpu: increase PERCPU_DYNAMIC_SIZE_SHIFT on DEPT and large PAGE_SIZE

Byungchul Park <[email protected]> Mon, 6 Jul 2026 15:19:26 +0900
Newsgroups org.kernel.vger.rcu,dev.linux.lists.linux-rt-devel,org.freedesktop.lists.dri-devel,org.kernel.vger.linux-arch,org.kernel.vger.linux-block,org.kernel.vger.linux-doc,org.kernel.vger.linux-ext4,org.kernel.vger.linux-fsdevel,org.kernel.vger.linux-i2c,org.kernel.vger.linux-ide,org.kernel.vger.linux-kernel,org.kernel.vger.linux-media,org.kernel.vger.linux-modules,org.kernel.vger.linux-nfs,org.kernel.vger.netdev,org.kernel.vger.rust-for-linux,org.kvack.linux-mm
Message-ID <[email protected]> 
Yunseong reported a build failure due to the BUILD_BUG_ON() statement in
alloc_kmem_cache_cpus().  In the following test:

  PERCPU_DYNAMIC_EARLY_SIZE < NR_KMALLOC_TYPES * KMALLOC_SHIFT_HIGH * sizeof(struct kmem_cache_cpu)

The following factors increase the right side of the equation:

  1. PAGE_SIZE > 4KiB increases KMALLOC_SHIFT_HIGH.
  2. DEPT increases the size of the local_lock_t in kmem_cache_cpu.

Increase PERCPU_DYNAMIC_SIZE_SHIFT to 11 on configs with PAGE_SIZE
larger than 4KiB and DEPT enabled.

Reported-by: Yunseong Kim <[email protected]>
Signed-off-by: Byungchul Park <[email protected]>
---
 include/linux/percpu.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/linux/percpu.h b/include/linux/percpu.h
index 85bf8dd9f087..dd74321d4bbd 100644
--- a/include/linux/percpu.h
+++ b/include/linux/percpu.h
@@ -43,7 +43,11 @@
 # define PERCPU_DYNAMIC_SIZE_SHIFT      12
 #endif /* LOCKDEP and PAGE_SIZE > 4KiB */
 #else
+#if defined(CONFIG_DEPT) && !defined(CONFIG_PAGE_SIZE_4KB)
+#define PERCPU_DYNAMIC_SIZE_SHIFT      11
+#else
 #define PERCPU_DYNAMIC_SIZE_SHIFT      10
+#endif /* DEPT and PAGE_SIZE > 4KiB */
 #endif
 
 /*
-- 
2.17.1