linux-kernel - Re: [PATCH v5 6/7] locking/lockdep: Reuse freed chain

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Message-ID: <f475cd25-2b63-39bc-c18c-14ac7274428b@redhat.com>
Date:   Wed, 5 Feb 2020 08:59:22 -0500
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, Bart Van Assche <bvanassche@....org>
Subject: Re: [PATCH v5 6/7] locking/lockdep: Reuse freed chain_hlocks entries

On 2/5/20 4:41 AM, Peter Zijlstra wrote:
> On Tue, Feb 04, 2020 at 11:45:15AM -0500, Waiman Long wrote:
>> On 2/4/20 7:36 AM, Peter Zijlstra wrote:
>>> --- a/kernel/locking/lockdep_proc.c
>>> +++ b/kernel/locking/lockdep_proc.c
>>> @@ -278,9 +278,11 @@ static int lockdep_stats_show(struct seq
>>>  #ifdef CONFIG_PROVE_LOCKING
>>>  	seq_printf(m, " dependency chains:             %11lu [max: %lu]\n",
>>>  			lock_chain_count(), MAX_LOCKDEP_CHAINS);
>>> -	seq_printf(m, " dependency chain hlocks:       %11lu [max: %lu]\n",
>>> -			MAX_LOCKDEP_CHAIN_HLOCKS - nr_free_chain_hlocks,
>>> +	seq_printf(m, " dependency chain hlocks used:  %11lu [max: %lu]\n",
>>> +			MAX_LOCKDEP_CHAIN_HLOCKS - (nr_free_chain_hlocks - nr_lost_chain_hlocks),
>>>  			MAX_LOCKDEP_CHAIN_HLOCKS);
>>> +	seq_printf(m, " dependency chain hlocks free:  %11lu\n", nr_free_chain_hlocks);
>>> +	seq_printf(m, " dependency chain hlocks lost:  %11lu\n", nr_lost_chain_hlocks);
>> I do have some comments on this. There are three buckets now - free,
>> lost, used. They add up to MAX_LOCKDEP_CHAIN_HLOCKS. I don't think we
>> need to list all three. We can compute the third one by subtracting max
>> from the other two.
>>
>> Something like:
>>
>> diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
>> index 14932ea50317..6fe6a21c58d3 100644
>> --- a/kernel/locking/lockdep_proc.c
>> +++ b/kernel/locking/lockdep_proc.c
>> @@ -278,9 +278,12 @@ static int lockdep_stats_show(struct seq_file *m,
>> void *v)
>>  #ifdef CONFIG_PROVE_LOCKING
>>         seq_printf(m, " dependency chains:             %11lu [max: %lu]\n",
>>                         lock_chain_count(), MAX_LOCKDEP_CHAINS);
>> -       seq_printf(m, " dependency chain hlocks:       %11lu [max: %lu]\n",
>> -                       MAX_LOCKDEP_CHAIN_HLOCKS - nr_free_chain_hlocks,
>> +       seq_printf(m, " dependency chain hlocks used:  %11lu [max: %lu]\n",
>> +                       MAX_LOCKDEP_CHAIN_HLOCKS -
>> +                       (nr_free_chain_hlocks + nr_lost_chain_hlocks),
>>                         MAX_LOCKDEP_CHAIN_HLOCKS);
>> +       seq_printf(m, " dependency chain hlocks lost:  %11lu\n",
>> +                       nr_lost_chain_hlocks);
>>  #endif
>>  
> Sure, also I tihnk the compiler is unhappy about %lu vs 'unsigned int'
> for some of them.
>
Yes, I found that after I compiled the code :-)

Cheers,
Longman