netdev - Re: [PATCH] prevent the read ahead of /proc/slabinfo in ss take 2

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Message-ID: <CAC2pzGci9FG+b=mgn9JQC58=VtX9Gf4aHZQOYiNj9Twb+oc3aA@mail.gmail.com>
Date:	Tue, 10 Feb 2015 13:48:52 +0800
From:	Bryton Lee <brytonlee01@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	stephen@...workplumber.org, netdev@...r.kernel.org,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH] prevent the read ahead of /proc/slabinfo in ss take 2

On Tue, Feb 10, 2015 at 12:49 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Tue, 2015-02-10 at 10:46 +0800, Bryton Lee wrote:
>> ss reads ahead of /proc/slabinfo whatever slabstat will be used or not in future.
>> this will cause huge system delay when the kernel hires SLAB allocator(SLUB allocator is ok). when program reads
>> /proc/slabinfo, it will call s_show() in SLAB allocator level, and s_show() calls spin_lock_irq(&l3->list_lock)
>> then iterate on whole three lists. if one slab has about 900 million objects (for example dentry),
>> it will cause more than 1000ms delay.
>>
>
> Please keep lengths < 70 chars in changelog.
>
>> so this patch prevents the read ahead of /proc/slabinfo, ss runs with most parameters not using slabstat at all.
>> and this patch also change slabstat and slabstat_valid to static.
>>
>> Signed-off-by: Bryton Lee <brytonlee01@...il.com>
>> ---
>>  misc/ss.c | 11 ++++++++---
>>  1 file changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/misc/ss.c b/misc/ss.c
>> index 7fc0a99..5fa6259 100644
>> --- a/misc/ss.c
>> +++ b/misc/ss.c
>> @@ -616,7 +616,8 @@ struct slabstat
>>       int skbs;
>>  };
>>
>> -struct slabstat slabstat;
>> +static struct slabstat slabstat;
>> +static int slabstat_valid = 0;
>
> David pointed that you never set this variable to 1 or any value...
>
> Why is this variable needed, if its content is known/constant ?
>
>
> I presume you wanted to set it in get_slabstat(), right ?

Yes, you are right. I missed it when I merged code from my local
version to upstream, big thanks to you!  I will commit it soon.

>
>>
>>  static const char *slabstat_ids[] =
>>  {
>> @@ -2230,6 +2231,9 @@ static int tcp_show(struct filter *f, int socktype)
>>        * it is able to give us some memory for snapshot.
>>        */
>>       if (1) {
>> +             if (!slabstat_valid)
>> +                     get_slabstat(&slabstat);
>> +
>>               int guess = slabstat.socks+slabstat.tcp_syns;
>>               if (f->states&(1<<SS_TIME_WAIT))
>>                       guess += slabstat.tcp_tws;
>> @@ -3196,6 +3200,9 @@ static int print_summary(void)
>>       if (get_snmp_int("Tcp:", "CurrEstab", &sn.tcp_estab) < 0)
>>               perror("ss: get_snmpstat");
>>
>> +     if (!slabstat_valid)
>> +             get_slabstat(&slabstat);
>> +
>>       printf("Total: %d (kernel %d)\n", s.socks, slabstat.socks);
>>
>>       printf("TCP:   %d (estab %d, closed %d, orphaned %d, synrecv %d, timewait %d/%d), ports %d\n",
>> @@ -3543,8 +3550,6 @@ int main(int argc, char *argv[])
>>       argc -= optind;
>>       argv += optind;
>>
>> -     get_slabstat(&slabstat);
>> -
>>       if (do_summary) {
>>               print_summary();
>>               if (do_default && argc == 0)
>
>



-- 
Best Regards

Bryton.Lee
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