It was found by Qian Cai that lockdep splat sometimes appears with the "BUG: MAX_LOCKDEP_ENTRIES too low" message on linux-next. On a 32-vcpu VM guest with a v5.7-rc7 based kernel, I looked at how many of the various table entries were being used after bootup and after a parallel kernel build (make -j32). The tables below show the usage statistics.
After bootup: Table Used Max %age ----- ---- --- ---- lock_classes[] 1834 8192 22.4 list_entries[] 15646 32768 47.7 lock_chains[] 20873 65536 31.8 chain_hlocks[] 83199 327680 25.4 stack_trace[] 146177 524288 27.9 After parallel kernel build: Table Used Max %age ----- ---- --- ---- lock_classes[] 1864 8192 22.8 list_entries[] 17134 32768 52.3 lock_chains[] 25196 65536 38.4 chain_hlocks[] 106321 327680 32.4 stack_trace[] 158700 524288 30.3 Percentage-wise, it can be seen that the list_entries for direct dependencies are used much more than the other tables. So it is also the table that is mostly likely to run out of space when running a compex workload. To reduce the likelihood of running out of table entries, we can increase MAX_LOCKDEP_ENTRIES by 50% from 16384/32768 to 24576/49152. On a 64-bit architecture, that represents an increase in memory consumption of 917504 bytes. With that change, the percentage usage of list_entries[] will fall to 31.8% and 34.9% respectively to make them more in line with the other tables. Signed-off-by: Waiman Long <long...@redhat.com> --- kernel/locking/lockdep_internals.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h index baca699b94e9..6108d2fbe775 100644 --- a/kernel/locking/lockdep_internals.h +++ b/kernel/locking/lockdep_internals.h @@ -89,12 +89,12 @@ static const unsigned long LOCKF_USED_IN_IRQ_READ = * table (if it's not there yet), and we check it for lock order * conflicts and deadlocks. */ -#define MAX_LOCKDEP_ENTRIES 16384UL +#define MAX_LOCKDEP_ENTRIES 24576UL #define MAX_LOCKDEP_CHAINS_BITS 15 #define MAX_STACK_TRACE_ENTRIES 262144UL #define STACK_TRACE_HASH_SIZE 8192 #else -#define MAX_LOCKDEP_ENTRIES 32768UL +#define MAX_LOCKDEP_ENTRIES 49152UL #define MAX_LOCKDEP_CHAINS_BITS 16 -- 2.18.1