On 10/23/19 12:17 PM, Waiman Long wrote:
> On 10/23/19 12:10 PM, Michal Hocko wrote:
>> On Wed 23-10-19 10:56:30, Waiman Long wrote:
>>> On 10/23/19 6:27 AM, Michal Hocko wrote:
>>>> From: Michal Hocko <mhocko@xxxxxxxx>
>>>>
>>>> pagetypeinfo_showfree_print is called by zone->lock held in irq mode.
>>>> This is not really nice because it blocks both any interrupts on that
>>>> cpu and the page allocator. On large machines this might even trigger
>>>> the hard lockup detector.
>>>>
>>>> Considering the pagetypeinfo is a debugging tool we do not really need
>>>> exact numbers here. The primary reason to look at the outuput is to see
>>>> how pageblocks are spread among different migratetypes therefore putting
>>>> a bound on the number of pages on the free_list sounds like a reasonable
>>>> tradeoff.
>>>>
>>>> The new output will simply tell
>>>> [...]
>>>> Node 6, zone Normal, type Movable >100000 >100000 >100000 >100000 41019 31560 23996 10054 3229 983 648
>>>>
>>>> instead of
>>>> Node 6, zone Normal, type Movable 399568 294127 221558 102119 41019 31560 23996 10054 3229 983 648
>>>>
>>>> The limit has been chosen arbitrary and it is a subject of a future
>>>> change should there be a need for that.
>>>>
>>>> Suggested-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>>>> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
>>>> ---
>>>> mm/vmstat.c | 19 ++++++++++++++++++-
>>>> 1 file changed, 18 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/mm/vmstat.c b/mm/vmstat.c
>>>> index 4e885ecd44d1..762034fc3b83 100644
>>>> --- a/mm/vmstat.c
>>>> +++ b/mm/vmstat.c
>>>> @@ -1386,8 +1386,25 @@ static void pagetypeinfo_showfree_print(struct seq_file *m,
>>>>
>>>> area = &(zone->free_area[order]);
>>>>
>>>> - list_for_each(curr, &area->free_list[mtype])
>>>> + list_for_each(curr, &area->free_list[mtype]) {
>>>> freecount++;
>>>> + /*
>>>> + * Cap the free_list iteration because it might
>>>> + * be really large and we are under a spinlock
>>>> + * so a long time spent here could trigger a
>>>> + * hard lockup detector. Anyway this is a
>>>> + * debugging tool so knowing there is a handful
>>>> + * of pages in this order should be more than
>>>> + * sufficient
>>>> + */
>>>> + if (freecount > 100000) {
>>>> + seq_printf(m, ">%6lu ", freecount);
>>>> + spin_unlock_irq(&zone->lock);
>>>> + cond_resched();
>>>> + spin_lock_irq(&zone->lock);
>>>> + continue;
>>> list_for_each() is a for loop. The continue statement will just iterate
>>> the rests with the possibility that curr will be stale. Should we use
>>> goto to jump after the seq_print() below?
>> You are right. Kinda brown paper back material. Sorry about that. What
>> about this on top?
>> ---
>> diff --git a/mm/vmstat.c b/mm/vmstat.c
>> index 762034fc3b83..c156ce24a322 100644
>> --- a/mm/vmstat.c
>> +++ b/mm/vmstat.c
>> @@ -1383,11 +1383,11 @@ static void pagetypeinfo_showfree_print(struct seq_file *m,
>> unsigned long freecount = 0;
>> struct free_area *area;
>> struct list_head *curr;
>> + bool overflow = false;
>>
>> area = &(zone->free_area[order]);
>>
>> list_for_each(curr, &area->free_list[mtype]) {
>> - freecount++;
>> /*
>> * Cap the free_list iteration because it might
>> * be really large and we are under a spinlock
>> @@ -1397,15 +1397,15 @@ static void pagetypeinfo_showfree_print(struct seq_file *m,
>> * of pages in this order should be more than
>> * sufficient
>> */
>> - if (freecount > 100000) {
>> - seq_printf(m, ">%6lu ", freecount);
>> + if (++freecount >= 100000) {
>> + overflow = true;
>> spin_unlock_irq(&zone->lock);
>> cond_resched();
>> spin_lock_irq(&zone->lock);
>> - continue;
>> + break;
>> }
>> }
>> - seq_printf(m, "%6lu ", freecount);
>> + seq_printf(m, "%s%6lu ", overflow ? ">" : "", freecount);
>> }
>> seq_putc(m, '\n');
>> }
>>
> Yes, that looks good to me. There is still a small chance that the
> description will be a bit off if it is exactly 100,000. However, it is
> not a big deal and I can live with that.
Alternatively, you can do
if (++freecount > 100000) {
:
freecount--;
break;
}
Cheers,
Longman
