linux-kernel - Re: [PATCH v2] neighbour: Don't let neigh_forced

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Date:   Wed, 6 Dec 2023 10:51:49 -0700
From:   David Ahern <dsahern@...nel.org>
To:     Stephen Hemminger <stephen@...workplumber.org>,
        Judy Hsiao <judyhsiao@...omium.org>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Simon Horman <horms@...nel.org>,
        Douglas Anderson <dianders@...omium.org>,
        Brian Haley <haleyb.dev@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Joel Granados <joel.granados@...il.com>,
        Julian Anastasov <ja@....bg>,
        Leon Romanovsky <leon@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH v2] neighbour: Don't let neigh_forced_gc() disable
 preemption for long

On 12/6/23 10:39 AM, Stephen Hemminger wrote:
> On Wed,  6 Dec 2023 03:38:33 +0000
> Judy Hsiao <judyhsiao@...omium.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.