Re: [PATCH v2] neighbour: Don't let neigh_forced_gc() disable preemption for long

[David Ahern <dsahern@kernel.org>]

On 12/6/23 10:39 AM, Stephen Hemminger wrote:
> On Wed,  6 Dec 2023 03:38:33 +0000
> Judy Hsiao <judyhsiao@chromium.org> wrote:
> 
>> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
>> index df81c1f0a570..552719c3bbc3 100644
>> --- a/net/core/neighbour.c
>> +++ b/net/core/neighbour.c
>> @@ -253,9 +253,11 @@ static int neigh_forced_gc(struct neigh_table *tbl)
>>  {
>>  	int max_clean = atomic_read(&tbl->gc_entries) -
>>  			READ_ONCE(tbl->gc_thresh2);
>> +	u64 tmax = ktime_get_ns() + NSEC_PER_MSEC;
>>  	unsigned long tref = jiffies - 5 * HZ;
>>  	struct neighbour *n, *tmp;
>>  	int shrunk = 0;
>> +	int loop = 0;
>>  
>>  	NEIGH_CACHE_STAT_INC(tbl, forced_gc_runs);
>>  
>> @@ -278,11 +280,16 @@ static int neigh_forced_gc(struct neigh_table *tbl)
>>  				shrunk++;
>>  			if (shrunk >= max_clean)
>>  				break;
>> +			if (++loop == 16) {
> 
> Overall looks good.
> Minor comments:
> 	- loop count should probably be unsigned
>         - the magic constant 16 should be a sysctl tuneable

A tunable is needed here; the loop counter is just to keep the overhead
of the ktime_get_ns call in check.