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mm: percpu: increase PERCPU_DYNAMIC_SIZE_SHIFT on certain builds.

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Arnd reported a build failure due to the BUILD_BUG_ON() statement in
alloc_kmem_cache_cpus().  The test

  PERCPU_DYNAMIC_EARLY_SIZE < NR_KMALLOC_TYPES * KMALLOC_SHIFT_HIGH * sizeof(struct kmem_cache_cpu)

The factors that increase the right side of the equation:
- PAGE_SIZE > 4KiB increases KMALLOC_SHIFT_HIGH
- For the local_lock_t in kmem_cache_cpu:
  - PREEMPT_RT adds an actual lock.
  - LOCKDEP increases the size of the lock.
  - LOCK_STAT adds additional bytes plus padding to the lockdep
    structure.

The net difference with and without PREEMPT_RT is 88 bytes for the
lock_lock_t, 96 bytes for kmem_cache_cpu due to additional padding.  This
is enough to exceed the 80KiB limit with 16KiB page size - the 8KiB page
size is fine.

Increase PERCPU_DYNAMIC_SIZE_SHIFT to 13 on configs with PAGE_SIZE larger
than 4KiB and LOCKDEP enabled.

Link: https://lkml.kernel.org/r/20241007143049.gyMpEu89@linutronix.de
Fixes: d8fccd9ca5 ("arm64: Allow to enable PREEMPT_RT.")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202410020326.iaZIteIx-lkp@intel.com/
Reported-by: Arnd Bergmann <arnd@kernel.org>
Closes: https://lore.kernel.org/20241004095702.637528-1-arnd@kernel.org
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Sebastian Andrzej Siewior 2024-10-07 16:30:49 +02:00 committed by Andrew Morton
parent e142cc87ac
commit 8f3ce3d996
1 changed files with 5 additions and 1 deletions
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6
include/linux/percpu.h
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@ -41,7 +41,11 @@
PCPU_MIN_ALLOC_SHIFT)
#ifdef CONFIG_RANDOM_KMALLOC_CACHES
#define PERCPU_DYNAMIC_SIZE_SHIFT 12
# if defined(CONFIG_LOCKDEP) && !defined(CONFIG_PAGE_SIZE_4KB)
# define PERCPU_DYNAMIC_SIZE_SHIFT 13
# else
# define PERCPU_DYNAMIC_SIZE_SHIFT 12
#endif /* LOCKDEP and PAGE_SIZE > 4KiB */
#else
#define PERCPU_DYNAMIC_SIZE_SHIFT 10
#endif